NEGATIVE ION/MOLECULE REACTIONS IN A NEGATIVE CORONA DISCHARGE Apri 1. 1981 by Vi etor Kotasek ":"
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Kluyver eg 1 - DELfTUTIAS Teehniea1 Note No. 230 CN ISSN 0082-5263
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NEGATIVE ION/MOLECULE REACTIONS IN A NEGATlVE CORONA DISCHARGE
Subroitted January, 1981
April, 1981
by
Victor Kotasek
UTIAS Technical Note No. 230 CN ISSN 0082-5263
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Acknowledgements
In appreciation for their support and informative discussions, I would like to thank Dr. J. B. French, Dr. B. A. Thomson, Dr. D. Douglas, Dr. S. Tanner, Dr. W. R. Davidson and Mr. J. Leffers. Also noted are Mr. H. Schumacher for bis careful construction of the ion source.
This work has been supported by the Ontario Ministery of Environment, Air Resources Branch, and the Natural Sciences and Engineering Research COUllCil of Canada, under grant No. A2731.
Abstract
An
atmospheric pressure negative corona discharge (point to plane)coupled to a quadrupele mass spectrometer was used to study negative
ion/molecule chemistry • It was shown that neutral int,ermediates, mainly
03'
N02
and NO, are produced by high energy electron dissociation of airconstituents in a very narrow volume close to the point electrode. The neutrals are transported by air flow or diffuse into the discharge gap
and undergo ion/molecule reaction initiated by the
02
and0-
ion. Atentati ve ion/mOlecule reaction scheme has been proposed. Furthermore
a reduction of the ions
N02,
N03' C03
and03
to less than 1% was possiblein zero air by flowing a nonelectranegative gas around the point electrode.
In room air ~he ions
N03' 03
andC03
have been reduced by approximatelyTable of Contents
Acknowledgements Abstract
A. NEGATIVE ION/MOLECULE REACTIONS I. rI. rIL IV. V. VI. VII. VIII. IX. X. XI. XII. INTRODUCTION
TRICHEL PULSE CORONA ION/MOLECULE REACTIONS EXPERIMENTAL APPARATUS THE ION SOURCE
THE INTERFACE GAS
ZERO AIR AND ROOM AIR MASS SPECTRVM VARlATIONS IN AIR FLOW
RADIAL NEEDLE MOVEMENT
TENTATIVE ION IDENTIFICATION VARIATION OF DISCHARGE CURRENT CONCLUSIONS B. ELECTRON THERMALIZATION I. EXPERIMENTAL rI. rIL REFERENCES
RESULTS AND DISCUSSION CONCLUSIONS
TABLES AND FIGURES
ii i i i 1 1 1 3 3 4 4 5 6 8 9 10 11 13 13 13
16
18..
A. NEGATIVE ION/IDLECULE REACTIONS
I. INTRODUCTION I
If air is subjected to an electrical discharge the formation of minor constituents, NO, 03, N02' etc., play a major role in determining the evolving ion/molecule chemistry. These species are important inter-mediates in the ionosphere and considerable effort has been undertaken to understand their chemistry. Their formation and reaction in an elec-trical discharge on the other hand are more difficult to elucidate due to the gener al complexities of electrical discharges •
If one wishes to trace an accurate chemical synthesis using micro-scopic parameters, it is necessary to know the electron energy and cross-sections for all processes. If the electric field is time dependent or non-uniform, or if space charge distortion of the original Laplacian field occurs, further camplications arise. Furthermore the tran-sport of neutrals formed by the discharge mayalso require consideration. Unfortunately all the information is not available. Negative ion mobilities and electron energy distributions are not accurately known at all values of E/N (Ref. 1). This is also true for many characteristic ionization and attachment coeffi-cients and chemical conversion coefficoeffi-cients. ' Computations (zero space charge) have been undertaken (Ref.
7)
to determine electron, negative ion and positive ion distributions in a negative point to plane discharge (air), but exact data is still not available for all the reactions invoived. Due to these complexities this particular study draws only qualitative conclusionssupported from literature when possible.
The technical note has been divided into two sections. The first section involves defining the ion source in terms of a negative ion mole-cule reactions and intermediate formation.* Section B considers techniques to control the ion molecule chemistry by diminishing the role of the inter-mediates. In order to appreciate the actual chemistry occurring in a negative point to plane or Trichel pulse corona, a basic understanding of its physical mechanism is necessary.
II. TRICHEL PULSE CORONA
If a negative voltage of sufficient magnitude is applied to the
stressed electrode, in this case the point, a triggering electron, liberated fram JDOlecular oxygen at same distance x in the gap will be accelerated by the electric field towards the anode. Ionization occurs until at same distance the ionization coefficient
a
equals the attachment coefficient ~. Positive ions formed in the gap will be swept back towards the cathode liberating further electrons through secondary processes and also serving to increase the ionization field leading to a rapid growth in current(Ref. 3). Spectroscopic measurements (Ref. 2) show that a luminosity develops at x, increasing in intensity and finally establishing a negative
*The terms intermediates or neutrals pertain to the species formed by electrical synthesis: N02, NO, 03, N20, etc. Similarly oxide ions or ozone derivatives refer to the negative ions formed through an inter-mediate, i.e., N02' N03, 03, or C03.
glow in front of the cathode. The negative glow cansists of the first negative system of N~ ions, as well as OI bands. Behind the negative glow a faint brushlike posi tive column develops but i t soon disappears as the negative glow intensity increases. The positive column cansists of only the second positive system of nitrogen molecules. The fast disappearance of the positive column is due to a lowering of the field by the negative glow (Ref. 2).
The majority of electron energy loss occurs through excitation of molecular nitrogen (Refs. 7, 17). With an energy of approximately .02 eV the electrons may be considered thermalized and will attach to oxygen molecules by a3-body collision process (Refs. 4-6). Electrons, constantly liberated from the cathode, create larger avalanches but these are increas-ingly checked by the positive and negative ion accumulation creating a field free region between the two space charges (Ref. 7). As the negative ions continue to accumulate the discharge is eventually choked off by a decreasing voltage in the ionization region. A new discharge develops when the negative ions have moved far enough away to raise the ionization voltage back to the self-sustaining value (Ref. 7). This does not neces-sarily imply that the negative space charge must clear the whole gap,
rather many space charges may be present in the gap simultaneously (Ref.
3).
Since nitrogen has a higher dissociation energy and lower number of dissociative states than oxygen it is not surprising NI bands wereun-detected in t~ spectroscopie study of Ikuta et al (Ref. 2). The formation of atomie nitrogen is believed to occur by the formation of a temporary negative ion (Refs. 10, 11). The
N2
ion forms on a repulsive curve at an energy greater than the dissociation energy of molecUlar nitrogen, 9.76 eV. This difference is equal to the electron affinity of atomie nitrogen. Dissociative recombination of electrons and positive ions may be neglected since close to the needle high electron and ion temperatures make this process unfavourable.Dissociation of oxygen can proceed by direct excitation to the upper B~ state with the probability of dissociation higher than the probability
of an optical transition to the ground state, or through a lower energy process, 3.6 eV, involving dissociative attachment producing 0 and 0-. The dissociative products are then excited by electron impact to produce the OI bands (Ref. 9). The formation of 0- close to the cathode (just beyond the positive space charge) is the primary reason for the choking off of the discharge (Ref.
8).
It is reasonable to expect a higher atomie oxygen density than atomic ni trogen. The atomic ni trogen and oxygen undergo re ac tions wi th molecular oxygen, reactions 2 and 8 listed in Table I (Table of Rate Constants), forming initially nitric oxide and ozone. 0- may be lost by reaction with carbon dioxide, reaction 51. 0- may also undergo an endothermic reaction with 02, 0- + 02 ~02 + 0. This reaction occurs at E/P values greater than 20 V/torr-cm, easily obtainable in this discharge. This reaction is probably the major depopulation reaction for 0-. There are indications that the formation of nitrogen dioxide occurs through oxidation of nitric oxide by ozone, reaction 10 (Ref. 20). This would seem to be a likely process since ozone concentrations are known to be very high in this discharge, as will be discussed later. The neutrals formed in the dis-charge region will by fluid transport enter the disdis-charge gap and undergo
a reactive sequence initiated by the 02 ion. This region of the gap is called the ion/molecule reactor.
lIl. ION/MOLECULE REACTIONS
The possible ion/molecule reactions occurring at atmospheric pressures and thermal energies are listed in Table I. The values for k (thermal) have been obtained fram recent literature.
It is to be expected that any ions formed at atmospheric pressure , will rapidly hydrate. Rate constant values for reactions involving heavily
clustered ions are not well known, but in general exothermic binary reaction rates will be reduced (Ref. 25). It is known that hydration of 03 slows the switching reaction to carbon dioxide and this reaction may become endo-thermic if 03 is heavily hydrated (Ref. 14). Charge transfer reactions
with one species hydrated would be less likely to reflect changes in reaction pathways, although this is by no means certain (Ref. 14). The
02
ion, besides undergoing thermal reactions with intermediate species formed by the discharge, will react by chemical ionization with neutral contaminants. Molecular oxy-gen has an electron affinity of .440 ± .008 - .46 ± .05 eV (Ref. 16), and will charge transfer to any species which has a higher electron affinity. This charge transfer may occur with nitrogen'dioxide, chlorine, nitrobenzene, and many more compounds (see Ref. 16). 02 will also abstract a proton from a species with a gas phase acidity greater than that of H02. Some compounds which do have a gas phase acidity larger than hydrogen superoxide are formicacid, acetone, or barbituric acid. More examples may be found in Ref. 21.
IV. EXPERIMENTAL APPARATUS
The system used is a commercially available (Sciex Ltd.) quadrupole mass spectrometer originally designed for hypersensitive detection of trace
contaminants present in aIDbient air. This ~stem has been described in great detail (Ref. 22), but briefly it employs an atmospheric corona dis-charge source with use in either a negative or positive mode, a high flow
rate sampling system (9 l/min - 100 l/min)
*
to ensure minimum memoryeffects, a nitrogen interface curtain to prevent orifice clogging by par-ticulate matter and a cryogenically cooled vacuum sYstem. The trace atmos-pheric gas analyzer (TAGA 2000) uses atmosatmos-pheric pressure chemical ionization to provide ppt detection of airborne contaminants. In the positive mode a rapid sequence of reactions produces hydrated hydronium ions of the type
H30+(H20)n which ionize trace species by non-fragmentation chemical ionization. In the negative mode thermalized electrons attach to molecular oxygen producing ions of the type 02(H20)n' These ionize trace species by charge transfer _ reacti9ns or proton abstraction. Other stable ions of the type 03' N0
2,
N03 and C03 are produced by the discharge due to high electrical power dissipatlon close to the point electrode.A photograph of the mass spectrometer and associated electronics is shown in Fig. 1-1. Ions produced by the point electrode (sewing needle) are attracted to the posi ti vely charged interface plate. A small percent-age of the total ion signal enters the orifice and is focussed by a series of lenses into the quadrupole. Ions then enter the channeltron electron multiplier to produce a pulse for each ion which is amplified and measured *These are old values fram Ref. 22 and rnay not apply here.
with aratemeter. An analogue output may also be obtained. The potential difference between the orifice (L9) and the cluster breaker lens (L10) may be varied to cause collision induced stripping of water from the ions. If this potential difference is large enough collision induced dissociation will result. Figure 1-4 shows the effects on relative ion intensity with an increasing voltage on lens L9.
V. TEE ION SOURCE
Figure 1-2 are photographs of the ionizing source used. Originally designed by Sciex but modified here, this source provides lateral and radial needle movement to optimize ion signals, study ion/molecule kinetics and ~
obtain information on trace neutrals distributions in the discharge. Measured applied point electrode voltages range fram 2.8 kV to 4.2 kV producing currents fram 1 ~A - 10 ~A respectively. Values up to 20 ~A may also be obtained. The interface plate (anode) was held constant at +450 volts above ground. Under normal operation the applied voltage is electronically regulated so as to maintain a constant discharge current. A negative point plane DC discharge at low voltages produces a pulsing current, Trichel pulse. In this case the pulse frequency is estimated to be between 50 and 100 kH (Ref. 3).
The inlet sample tube for ambient air analysis has an inner diameter of 1.8 cm. Air-is drawn through this tube by way of an air pump to the discharge chamber connection as shown in Fig. 1-2. When campressed air (zero air) was used as the carrier gas one end of the inlet tube was
reduced to a diameter of .6 cm. If the zero air flow is 79 cc/s (10 scfh) velocities past the needle will be similar to velocities when the larger diameter tubing and air pump are used. With the zero air as a carrier gas the connection to the air pump was removed to keep the discharge chamber
at atmospheric pressure. The glass tube, shown in Fig. 1-3, is used to confine a nonelectronegative shrouding gas to the ionization region in an effort to produce thermalized electrons. This experiment will be discussed in Section B.
VI. TEE INTERFACE GAS
Matheson UHF nitrogen flows between the orifice and interface plate preventing particulate clogging of the orifice and atmospheric air from entering the mass spectrometer. Some interface gas flows into the discharge chamber through~a .6 cm opening producing a stagnation point where the air and nitrogen meet. This balance between the two flows is a momentum balance and the stagnation point may be moved by increasing or decreasing either the zero air or interface gas flows. This provides an opportunity for controlling the reaction kinetics by varying reaction time. To a significant extent the nitrogen interface curtain will induce declustering ,of a clustered ion by reversing the equilibrium, ABn + B = ABn+l since no B is present in the curtain. If the lifetime of the cluster is longer than the time it spends in the interface gas, declustering may not result. Interface gas decluster-ing effects are easily inferred by turndecluster-ing the flow off. Peaks at 50, 68
and 76 amu increase. These ions are 02(H20), 02(H20)2 and C04 respectively. One possible explanation for the effects to be discussed below may be due to an increasedion/molecule reaction time with removal of the nitrogen
c~tain gas. With zero curtain flow and only zero air flow the 02 and 03 peaks are reduced significantly, whereas the 903, N02, and N03 peaks double in intensity. The reaction of the ions 02 and 03 with other species is not stopped prematurely by an interface gas zero air boundary, but instead reactions may occur until the ions enter the orifice. This
is also true for C03 and N02 ions as well as the neutrals produced by the discharge, !.e., N02, NO, and 03. Thus the probability of charge
transfer from Ü2 to neutral ozone or nitrogen dioxide, reactions 13 and
l6l will ~e increased. The
0.2
ion will be re~uced in intensity but theN02 and 03 will increase in intensity~ The 03_ion will react with carbon
dioxide and_nitric oxide produc!ng C03 and NOl respectively. This re-duces the 03 intensity. The N03_ion mayalso oe produced by reaction of
neutral nitrogen dioxide with 03' reaction 25. An increased reaction
time due to removal of the nitrogen interface gas is one possible
explanation accounting for the effects on ion intensity. Another contri-buting factor may be due to the occurrence of wall reactions. Molecules
or atams may bond to the interface plate (02,
°
and organics). Thesesurface absorbants could be released by electron or ion bombardment.
These species could react close to the interface surface with the
mole-cular oxygen present in the atmospheric air. With the interface gas flowing the atmospheric oxygen present near the surface would be insig-nificant, resulting only from impurities in the nitrogen curtain. Wall
reactions are difficult to decipher and a possible reaction mechanism
accounting for the above effects on ion intensity is not obvious.
VII. ZERO AIR AND ROOM AIR MASS SPECTRUM
There are some obvious differences between the two spectra., al though
the major ions, 0-, 02, 03, N02, C03 and N03, are present in both. Com-paring Figs. 2-1 and 2-2 it will be noticed that peaks at mass 17, 33, 45, 59, 61 and 77 amu are found in roam air but with very low intensity
in zero air. The peak at 17 amu is the hydroxide ion formed by reaction
40 or 42. Ma~ses at 61 and 77 amu are OH- clustered to C02 and HC04.
Thus same species found in room air are due to high water levels. This is also suggested by the absence of the NO+ ion in the positive ion room
air spectra, fig. 2-7 although NO+ is present in zero air, Fig. 2-4. In
moist air the NOT ion is converted to H30T (H20) by successive clustering reactions (Ref. 23). NO+ (H 20) + ~O + M + NO (H20)2 + H20 + M NO+ (H20)3 +
~O
NO + (H 20)2 + M NO+ (H 20)3 + H30 (H20)2 + HN02The presence of the C04 peak, 76 amu, and C04 (~O) peak, 94 amu, also
would indicate a higher water level in room air. C04 is formed by the
switching reaction with 02 (H20). H~wever af ter one hydration of C04
the C02 is replaced by H20 forming Û2 (H20), a more favourable
thermo-dynamic process. The ions at 33, 45 and 59 amu are organic traces present in the room air. The identification of these ions and others is left to a later section.
Figure 2-2 shows very intense 03 and ~03 peaks. In room air_the oxide current has been lowered except for the N02 ion. Although the NOl ion is shown larger in zero air this is not usual and it may depend on tne time the discharge was on. Large quant i ties of 0.3 and C0.3 indi cate ozone builds up in the chamber under zero air flow conditions. This is confirmed by observations to be discussed later. Furthermore the addi tion of ozone (approximately 1 ppm) produces no ~ignificant change in the ion current (Ref. 13). In room air the high flows 150-1600 cc/s will dilute and mini-mize the concentration of neutral species produced by reactions at the need.le tip. Figure 2-8 shows the
02
signal as moni tored in room air at an air flow of approximately 800 cc/ s. The peak-to-peak noise is approximately 300,000 cts/s. The ion signals of N0.3, N02, C03 and 03 also exhibit this noise, although the magnitude varies samewhat for the different species. At this typical flow rate of 800 cc/s the Reynolds number is approximately Re = 3900. This value is above the turbulent value, Re = 2000, and oneexpects local fluctuations in the number densities of the neutral species, N02, NO and 03. This would J?roduce random changes in the
02
population,since the reactive loss of Û2 is dependent on the concentration of the neutrals N02 and 03. In zero air a flow rate of 79 cc/s gives a Reynolds number of Re
=
1100. Thus the flow is laminar and perturbations in the neutral densi ty by the flow would be negligible. The ion signals in zero air are very stable.VIII. VARIATIONS IN AIR FLOW
With the point electrode on the discharge axis and a gap distance of 10 mm the zero air flow was varied from 16 cc/s (2 scfh) to 110 cc/s (14
scfh). A graphical illustration of this effect on normalized peak height is shown in Figs. 3-1 and 3-2. These curves represent d eclustered and clustered ions r~spectively. It is interesting to note the ion signals 03, N02, N03 and CÛ3, as well as their clustered counterparts, ~ncrease in intensity ~s
the flow rate past the need.le is increased. The 0 sign~l follows the 03 signal since it is mainly derived fram declustering of Û3_in the high field
region between L9 and L10. The exponential decrease of Û2 suggests an
increasing concentration of intermediates entering the ion/molecule reactor. This effect has been reported in the past (Gardiner et al, Ref. 15). Here a negative point to plane corona discharge was used as the ion source but the discharge chamber pressure was only 10 torr. Pure nitrous oxide was used as the carri~r gas and ion analysis performed with a mass spectro-meter. It was found at low flow rates that the
02
peak was the dominant ion. This was attributed to 0 reacting at the walls to produce molecular oxygen. At high ilow rates the 02 ion intensity was reduced by a factor of 4 and the 0- ion intensity increased by the same factor. They suggested that the higher flow rates prevent diffusion away fram the gap axis. This could also be occurring in this experiment. It was found that flow ratesless than 31 cc/s (4 scfh) produce a slowly rising and slowly fluctuating increase in oxide current. The increase in relative peak height may be seen by examining Fig. 3-2. At these low flow rates the species produced by the discharge s,lowly build up in the plenum chamber diffusing into the gap. This accounts for the slow variation in signal. As the flow rate is increased the gap is cleared of a small percentage of the intermediates
producing a lower density and new equilibrium distribution. This distribu-tion is regulated by the high product ion rate of neutrals by the discharge , the flow rate and their ability to enter the ion molecule reactor. At higher
'flow rates fewer species are lost to nonreactive diffusion and more enter the ion molecule reactor. Even though we are constantly diluting this volUlDe the production rate near the needle for these species is so high that we have prevented a larger proportion from being lost. A maximum flow should exi st such that an increase will tend to dilute the neut ral intermediates causing the oxide current to fall. It is also possible that a certain percentage of species will be lost in the discharge V01UlDe by ionization or dissociation unless removed fast enough. Trichel pulse periods are tenths of microseconds and flow velocities only 100 to 200 cm/s. In room air, the flow rate is not accurately known but as mentioned i t i s higher than the zero air flow. The velocity far fiom the needle would also be expected to be higher. These
effects obviously dilute and minimize any buildup of neutral intermediates in the gap and discharge V01UlDe. Diffusion effects would be less important in this case.
The interface gas flow plays only a small role in affecting reaction time and transport of neutrals. Figure 3-3 shows the effect of increasing interface gas flows with the other parameters, zero air flow, needle position and spacing remaining the same as mentioned at the beginning of this section. The 02 signal was monitored with the channeltron voltage reduced, accounting for its small relative intensity. Although the change in ion signal was not dramatic i t does tend to mimic the floweffects over small range. An inter-face gas flow rate varied from approximately 20 cc/s to 40 cc/s would corre-spond to a stagnation point located approximately in the same position if the zero air flow was varied from 31 cc/s to 16 cc/s. Although
02,
02(H20) and mass 34 amu (~80 160-) increase to a maximum at an approximate flow of 30 cc/s, and the oxide species decrease to a minimum, the oxide species again increase as the interface gas flow reaches 40 cc/s. The formation of CO§ and NO~ involve more reaction steps and should not increase by decreasing the tlme spent in the gap. It is possible that neutrals are being concentrated in the gap by the higher interface gas flow. This would tend to increase the ozone derivatives. Also if the H2 curtain is close to the needle, electron attach-ment and thermalization would decrease. The higher energy electrons would tend to dissociate more N2 and 02, accounting for the small increase in the ozone derivatives.If the needle is moved radially off the discharge axis, corresponding to an arc length of approximately 3 mm, then a variation of zero air flow produces the curves shown in Fig. 3-4. Examination of these curves shows that only a small change in normalized peak intensity occurs when the flow rate is varied from 31 cc/s to 110 cc/s. A major increase in the oxide current occurs at flows less than 31 cc/s.
These effects are related to the flux of intermediates into the ion molecule reactor. With the needle 3 mm off the discharge axis and thus out of the direct stream flow, the transport of intermediates into the ion mole-cule reactor would be dramatically reduced and would occur mainly through diffusion. In fact high flows may tend to inhibit their diffusion into the gap. At flows less than 31 cc/s the gap is not cleared fast enough to
suppress diffusion of the neutrals and the oxide current increases. It is obvious from Figs. 3-1 and 3-2 that reactions are aided by the increased zero air flow. To accurately predict reaction channels, the fluid flow and its effects on the density of discharge products in the gap and discharge volume would have to be known. But there is a basis for proposing a tenta-tive model of the ion/molecule reaction kinetics. This is shown in Fig. 3-5. The decrease in
02
is almost exponential. The species that next increases is 03 followed by N02 which changes "'!,ery little with flow. 03 would be formed by the charge transfer from Û2. This is a fast exothermic reaction and shO'uld not be drastically impeded by clustered02.
It may be thought that the N02 signal should follow the 03 signal, ~ince neutral ozone is a likely species to oxidize nitric oxide, and the Û2 ion is the most probable species for charge transfer. But since the charge transfer to ozone is faster,k0
3=
6(-10) .cm3/mol/s, compared to kN02=
1.2(-10) cm/mol/s, then the 02 population should be depleted quickly enough to prevent a fast reaction with ni trogen dioxide. The rise in the N02 signal wO'uld be slowed and also i ts increase would be held in check by rapid conversion of nitrogen dioxide to N03' reactions 25 and 30.03 c·lusters IIp_to n
=
3 are observed (Fig. 3-2), and it is expected the slow ri se in the C~ signal is due to a reduction of this exothermic switching reaction. It is no~ clear from t~is da~a alone if N03 is formed by neutral ni trogen dioxide reacting with C~ or 03. It wo~d seem likely that b~th re~ctions_would occur. Another way of forming N03 is by reaction of <>2 (H20 ) , C04, or 04 with nitric oxide. These conversion processes are fast, k ~.5 - 3.0(-10) c~/mol/s (Ref. 27), and produce the peroxy isomer of N03(-00NO). This isomerie form should be removed by declustering in the high field region between the orifice and cluster breaker , producing NO and
02.
Thethermo-dynamic threshold for this reaction is .9 eV (Ref. 27). This is half the association energy of the
° -
02 bond and 03 is clearly dissociated by de-clustering. .It is difficult to do a kinetic study in this system since the neutrals formed by the discharge are in high concentrations, thus saturating reactions. One propos al might be to selecti vely eliminate certain reaction steps. For instance, if the association of water to 03 can be made very efficient, then any switching reaction involving carbon dioxide or nitric oxide would become endothermic. In this sense the N02 ion would appear only if formed at the needle. This assumes the charge transfer reaction by 02(H20) to N02 is not af'fected.
IX. RADIAL NEEDLE MOVEMENI'
Figures 4-1 and 4-2 are the results of radial needle movement at a gap distance of 8 mm and 12 :mm respectively. The needle movement corresponds to an arc of approximately 6 mmo The arbitrary units 1 and 3 in the figures 4-1 and 4-2 correspond to opposite sides of the inlet tube. Zero air flows for these two gap distances was 79 cc/s. Also, the needle-to-inlet tube distance was kept constant at 2 mmo Wi th a maximum radial needle movement of 3 mm an approximate
&/0
drop in total ion current occurred. As the gap distance was increased from8
mm to 12 :mm a drop of 14% in ion currentoccurred. Also, due to the conical shaped interface plate, a radial movement of 3 mmproduced a measured voltage increase of approximately 150-200 volts.
The constant current source used in these experiments will compensate for a voltage increase and a drop in applied voltage will occur. Similarly the measured applied voltage at 12 mm increased by 600 volts from that at
8
mmo These are small changes and should not produce significant effects in terms of ion/molecule chemistry • As the gap distance is increased the current density decreases since the total current is contained in a larger volume. This means that relative changes in ion currents will be smaJ..ler when the needle is moved off the centrë axis. This is shown by a spreading of the ion intensity in Fig. 4-2.It is apparent from Figs. 4-1 and 4-2 that neutrals are formed in a discharge volume close to the needle. The evolution to final product ion depends on the flux of these neutrals into the ion/molecule reactor. The neutrals are aided by the fluid flow in this system, so that if the ne edle is maved out of the flow stream, only slow diffusion into the ion molecule reactor occurs. At these positions, far from the discharge axis, the ions which originate from intermediates will be at a minimum.
Radial movement of the needle also implies the 03 ion is not produced in large quantities at the needle by a three-body collision between 0- and 02. This is also suggested by the flow data just discussed. It means th at the majority o!
03
originates from neutral ozone which undergoes charge transfer with the Ü2 ion. As will be discussed in the .following section, radial needle movement can aid in the detection of those trace contaminants present in arnbi-ent air. Improved detection limits will be possible since these species will not enter a region of high energy electrons. This, combined with other tech-niques as will be discussed in Section B, should eliminate a large proportion of background ions formed by the discharge.x.
TENTATIVE ION DJENTIFICATIONAs noted in the previous section and in Section VIII, it is possible due to the product ion of neutral intermediates close to the needle and the transport of these species into the ion/molecule reactor to classify ions as 02 derivatives or
o§
derivatives. In this instance the rate of transport of neutrals is affected, but in Section B it will be seen th at the rate ofproduct ion may also be changed. Complete elimination of neutral intermediates implies that the only ions seen are
02
clusters or trace contaminants present in the air.Consider first only the zero air study. The floweffects (Figs. 3-2, 2-13 and 2-14) are similar to radial needle movement (Figs. 2-5 and 2-6) since both involve transport of intermediates. Radial needle movements seem to have a much larger effect on the oxide current than does flow variation. Most ions are clustered
02
derivatives or clusteredo§
derivatives. These are listed in Table II. Interesting ions are at mass 64 and 78 amu. These ions may be N02(H20), 04, CC§(H20), or 02(H20) (N2)· The mass_at 64 amu behaves like an 03 derivative and is therefore N02(H20) rather than 04. This is also confirmed by the thermalization experiments in Section B, Figs. 6-5 to 6-16. The ion at 78 amu does not decrease while shrouding or with radial movement. The ion proposed,02 (H20)(N2) ,
ma:y not be thermodynamically stable. A calcu-lation of the free energy would have to be done. In order to do this the electrostatic bond energy of molecular nitrogen to the02
cluster would haveto be known and an approximation made for the molecule' s structure to obtain the rotational entropy. These ions in room air behave as 04 and C02(H20)
(Figs. 2-9 to 2-12 and 6-17 to 6-20). In room air there is a larger concen-tration of water molecules and 02 is observed to cluster up to n
=
4 (104 amu). 02 forms very stable water clusters and these are not in equilibrium with the lower hydrates (Ref. 25). Clustering of molecular nitrogen would not be ther-modynallÜcally favourable in ~his case. 04 should be reduced in room air since it is in equilibrium with C04 and C02 is displaced from this cluster as water concentrations increase. This has been shown by solving the rate equations at increasing H20 concentrations (Ref. 35). This ion may actually be N02(H20) since in room air there are very large N02 signals (Figs. 2-9 and 2-10). If nitrogen dioxide is present in the room air a chemical ionization reaction would take place, producing N02 followed by hydration to N02 (H20).XI • VARIATION OF DISCHARGE CURRENr
Using either room air or zero air, the discharge current was varied fram
1-10~. This corresponds to an applied corona voltage variation of 2.8 kV to 4.2 kV. Zero air flow rates were 79 cc/s whereas in room air the flow
rate was approximately 800 cc/s. The needle-to-interface spacing in both
cases was 10 mmo
Consider only the zero air study with the needle on the system's axis (Fig. 5-1). It is seen that a relative increase in 03' C~,_and N03 occurs as the discharge current is increased from 1-4 !lA. T"ne '&02 signal falls off at approximately 2~. The transition region from 4-7 !lA is marked by a fluctuating ion current and an increase in
02
derivatives. Af ter 7 !lA the current stabilizes.A similar discharge current effect has been reported in the past (Lecuiller
"et al, Ref.
5).
Using a negative point to plane corona discharge and atmosphericpressure oxygen with trace impurities, carbon dioxide and nitrogen, a transi-tional period occurre4 beginning at 30~. Below_30!lA 03 derivatives pre-dominate, while above 30 ~ ions are related to Û2. These effects were explained on the basis that an increasing current produces large quantities of 0, 0-, and 02 (l~). The increased density of dissociate~ oxygen provides a favourable enviro~ent f~r recombination reactions:
°
+°
~ 02 + e,20 + 02 ~ 202 and
°
+ 02(.6g)
~ 03 + e. These reactions leave behind a_slow electron which attaches to 02. With weak currents the densities of 0,°
and 02('Dg) are low enough that reactions with molecular oxygen predominate: 0- + 202 ~ 03 and°
+ 202 ~ 03. The high current s required in Lecuiller' s experiment are needed to prevent choking off of the discharge. In atmospheric air a transitional regime occurs at much lower voltages, 6 kV for a gap dis-tance of 20 mm (Ref. 12).One cannot make an exact comparison between Lecuiller' s experine nt and this one, even though the flow geometry is very similar, the discharge gases and fluid flow are quite different. As shown previously, this system is very sensitive to the fluid flow. This is seen here by a comparison of the effects of current variation in room air (Fig. 5-3), and those in zero air (Fig. 5-1). The needle positions are the same and measured applied corona voltages produced the same currents in both cases. One expects the same production rate of
neutrals, but with room air due to the higher flows neutrals will not be allowed to b-uild up to large densities. This would seem to be the only major difference between the room air study and zero air study. If the needle is
moved off the discharge axis (Fig. 5-3), then the ion currents tend to increase with increasing voltage. Far from the needle low densities of neutrals are expected but these species will be susceptible to transport by the fluid. As the current increases, the neutral density increases and the flow of
neutrals into the ion/molecule reactor will also increase. One could account for a drop in the ion current by applying Lecuiller' s reasoning and -the
depopulation reactions listed in Table I (neutral reactions). But there are also effects which he has not considered. If the flow does not remove large numbers of neutrals they would be stibjected to an increasing probability of ionization and dissociation by electron impact. This process would depend on the value of E/N in some region of the discharge. Attachment and ionization vary exponentially with the field and small distortions by space charges would be important.
By analogy with thermal rate constants involving colli sion between two species one may also define a rate constant involving a conversion process by electron impact. This rate constant would depend on the overlap between the croSS-Sèction and the electron energy distribution function (Ref. 30). One might expect a maximum value to exist for the rate constant in terms of con-version of molecules per eV. Then in the case of decomposition of molecules there would be same value of E/N at which decomposition would be most efficient. This is because the electron energy distribution depends on E/N. The minimum value of E/N for decomposi tion of ni tric oxide is 49 ± 1 Td and for nitrogen dioxide 110
±
10 Td (Ref. 31). These conversion processes convert nitric oxide and nitrogen diax:ide to molecular nitrogen and oxygen. Similarly there might be a minimum value for conversion of ozone to 0 and 02. This possibility of decomposition needs further investigation. It may help elucidate the actual kinetics occurring in the discharge volume.It wi11 be noticed (Figs. 5-2 and 5-3) that the C03 signal decreases with increasing current in room air and in zero air with the needle off the discharge axis. This would seem to indicate an ion/molecule reaction either with NO or N02. In both cases the N03 and N02 signals increase. It is not possible with the data gathered so far to be more precise. Figure 5-3,. room
air, shows the current variation was from 2 IJÀ to 10 IJÀ. A current of 1 !lA could not be maintained. This may be due to a change in the cathode surface due to organies present in the room air. Organic bombardment of the cathode may increase the work function of the metal. Again there seems to be no easy explanation for the processes occurring, although two interesting possibi1ities have been proposed. It would be advantageous to know the discharge current pulse shape and frequency since at low voltages an autostabilization regime exists marked by random pulses and very high fields at the cathode (Ref. 12). It has been shown in the past (Refs. 36, 37) that nitric oxide production in low pressure gl~ discharges may be increased by catalytic effects, i.e.
absorption of N2 ion on the cathode followed by liberation of atomic nitrogen. This process may be aided if high fields exist near the cathode.
XII. CONCLUSIONS
As has b~en shown, the corona chemistry occurring in air is very difficult to interpret • There seems to be no easy solution to this. The experiments
conducted have demonstrated same fundamental aspects of negative corona discharge chemistry and provided a basis for conducting future research in this difficult
area. It has been shown that neutral intermediates, NO, N02, and 03' are produced near the needle tip. By varying the air flow past the needle tip
it was possible to change the neutral intermediate density in the gap and therefore the intensity of the product ions,
03,
N02,
NO~, CO§, and02'
Radial movement of the needle off the discharge axis proQuces dramaticdecreases in all species formed by high electron processes, i.e. ozone deriva-tives. .AJ.though the neutraJ. intermediates are still being produced they are not aided by the air flow and only by slow diffusion do they enter the ion/ molecule reactor. Using the above as a basis, a tentative ion/molecule re~ctio~ model !as proposed showing the evolution of the main ions,
q2,
N02,
N~, Cû3, and 03' This is outlined in Fig. 3-5.With the needle off the discharge axis the main ions are
02
hydrates and clusters. This demonstrates a defini te advantage for performing trace detection of airborne contaminants with the needle off the discharge axis. The "soft" chemical ionization reactions are nore probable and also the traces will not enter a region of high electron energy thereby decreasing the proba-bility of fragmentation. Some trace species have been identified using this methode These are listed in Table II. Further refinement for maximizing chemical ionization processes and eliminating high energy electron impact dissociation of traces as weIl as elimination of the neutrals produced by the discharge and their counterpart ions is discussed in Section B, Electron Thermalization.Regarding future experimentation i t would probably be best to perform studies in uniform fields with known fluid flows. One could obtain information on the electrical synthesis or decomposition of the neutrals produced by the discharge • Modelling of the corona field by spectroscopie measurements and probe measurerents would be of interest in order to apply kinetic theory in a uniform field to the nonuniform corona field.
It may be useful to review literature with emphasis on metal catalytic agents and their effects on oxide synthesis. A change in the metallic cathode may elucidate the kinetics occurring near the needle tip. Perhaps a re agent molecule could be found such that the undissociated molecule or its fragments formed by the discharge could selectively attack neutral nitrogen dioxide or nitric oxide.
B. ELECTRON THERMALIZATION
I. EXPERIMENTAL
A nonelectronegative shrouding gas confined to the discharge region with glass tubes (Fig.
1-3)
provided a thermalization medium for high energyelectrons. The shrouding gases, nitrogen, argon, methane, and carbon dioxide, were Matheson ultra-high purity grades. The re agent gas was either Matheson zero air or room air. With zero air a flow rate of
79
cc/s was used giving a bulk gas velocity from the inlet tube of 248 cm/ s. The room air flow rat e was 800 cc/s which gives a bulk air velocity of314
cm/s.The glass tubes designated as A or B produced the most favourable results and although other variations were tried, these met with limited success. Tube C required large flows to produce a noticeable change in ion intensity, but this quickJ..y led to current breakdown. This effect was evident in both room air and zero air studie s • Tube IWvement parallel to the needle axi s was provided by using ~eflon plug holders (Fig.
1-3).
The tube position and therefore needle position varied for the wo types. Results were romparable if the needle position in tube A varied fr om a .5 to a 1.5 mm protrusion. With tube B the required needle position could be varied from a 1.5 mm needle depression to flush with the top of the glass.Shrouding gas flows were introduced by a Teflon tube through a Swagelok fitting in the discharge challlber (Fig. 1-2). Flow rates were measured with a rotameter and varied with a valve.
Ion peaks were monitored individually for variations in intensity with changing shrouding gas flow rates. The values quoted in Tables III to VIII are the ones providing a maximum reduction of the oxide ions.
II. RESULTS AND DISCUSSION
Tables III to VIII show the major ion currents as a percentage of the total current before and af ter shrouding. Also shown is the percent change in oxdie current due to shrouding.
Before discussing the actual electron thermalization result it should be noted that a large change in ion intensity occurs by the introduction of a glass shrouding tube into the discharge region. This is evident by com-paring Tables III and IV with Tables V to VIII, as well as a comparison of the room air spectrum (Figs. 6-1 and 6-2) without andwith tube B respectively. A decrease in oxide ions occurs as well as a corresponding increase in the
02
intensity. This effect is found with tube A but it is not as dramatic. This effect is due to the size af tube Band because the entire needle was located inside the tube. The air flow around the glass creates a low velocity point on the orifice side producing eddies and vortices. This effect may increase the concentration of neutrals in the discharge volume thereby increasing the probability of depopulation reactions, dissociation and positive ionization of neutrals. These processes lower the concentration of neutrals in the gapand therefore the ozone derivatives. As will be discussed later in this sec-tion, the corona properties may also be affected producing a similar phenomena observed when the current was increased. A:n alternative explanation is related to the high Reynolds number. At this flow rate eddies and vort ex trails exist on the orifice side of the tube reducing the neutrals entering the ion molecule reactor.
Withdrawal of the neutral intermediates would be a viable alternative to shrouding. This was tried but at most only a
5%
reduction in the oxide current was possible. A low pump speed, the narrew diameter opening from the glass tubes are. both contributing factors to this minimal re sult • A tube with a larger opening, and a pump wi th a higher throughput, may prove t 0 be anexcellent way of elimination of the neutrals. In relation to electron shrouding, Tables III to VIII show that neither tube A nor B is superior. The advantage of tube A over B involves a larger needle openj ng eliminatil1g
any problems with movement which would interfere with the shrouding gas flow. It has been found (Ref. 26) that the time for electron thermalization decreases if the collision gas possesses vibrational and rotational modes.
An
electron leaving the cathode surface would be accelerated until it loses energy through ionization, dissociation or excitation. Rare gases such as àrgon remove electron energy through inefficient elastic cOllisions, ionization and electronic excitation. Large molecules such as methane possess low level thresholds for vibrational ;md rotational excitation. In general, the "slowing down" of electrons will be most efficient when small amoilllts of energy are to bé transferred. Energy loss in argon can be seen from Tables IV and VI toreflect an inefficiency in thermalizing electrons. Although thermalization is certainly occurring it may not be as effective as suggested by the spectra in Figs. ~-
3
to6-14.
For example, increasing shrouding gas flows in zero air always produces slow increases in 02 derivatives or decreases in 02 derivatives, suggesting either that(1)
large numbers of neutrals are being slowly drawn along the lew pressure orifice side of the tube and then are transported into the ion molecule reactor, or (2) the neutrals are stillbeing produced at the needle but electron thermalization is not 100% efficient so these species are being reduced in concentrations by an increasing concen-tration of shrouding gas in the plenum chamber. There is some evidence to
suggest that the latter is partly occurring (Ref. 13). Furthermore the addition of carbon dioxide removes allozone (reaction
19).
If the carbon dioxide is turned off the rise in the03
ion to its original full value takes approximately ten minutes. Nitrogen or argon was not mixed with the zero air to see if a large decline in the oxide current occurs. This should be investigated further. Since these effects should be independent of the gas the ion spectra should be very similar if'no electron thermalization was taking place. A comparison of the spectra shows that this is not true and thermalization is occurring to some extent. Methane produces an almost oxide-free spectra (Figs. 6~5 to6-8),
but an examination of these figures indicates that 02. ions are being lost. Since dissociation of methane mayproduce neutral hydrogen or atomic hydrogen areaction could occur with the 02 ion near the interface gas air bOillldary producing H02 or H20. Another possibility is loss of the thermaJ.ized electrons by diffusion.
The CÜ2 shroud also seems to produce efficient electron thermalization although the corona current is unstable. This is due to electron attachment to carbon dioxide producing the 0- ion, CÜ2 + e ~ CO + On, followed by a rapid reaction to produce C~. This should be the only way for
C03
to be formed if the shrouding is eïficient. The increase in the peak at61
amu,HC03(H20) suggests lew levels of water are present in carbon dioxide.
The nitrogen shroud with tube A (Figs. 6-13 to 6-14) shows good removal of N02, N03 and C03' but
03
is still present. This could be caused by in-creased impurity levels (02) in the nitrogen.If the
02
peak intensity or its clusters are used as a measure of the ability of the gas to thermalize electrons then judging by the spectra N2 would prove to be the most efficient.The NO+ ion is present in zero air and shroudi:r;tg may prevent i ts forma-tion if it is formed by the exothermic reacforma-tions, N+ + 02 -t NO+ + 0 or
0+ + N2 -t NO+ + N. Using a nitrogen shroud (Fig. 6-16) the NO+ peak was
reduced by 64% and with \an argon shroud by
4&/0.
This may be an indication of the actual shrouding efficiency but it also could be due to an extension of the anode by the shrouding gas. In a positive corona discharge the posi-tive ions reach a maximum densi ty near the anode. This would extend the high field region closer to the cathode. Since argon has a higher ionization coefficient (Ref. 1) than nitrogen this field extension may be larger in an argon shroud than in a nitrogen shroud, explaining its poorer ability toremove NO+.
The room air shrouds required much higher shrouding gas flow rates. If a shrouding flow of 41 cc/sis used the veloc1ty of the gas is approximately 1400 cm/s. Effective shrouding was obtained with nitrogen and room air using tube B at a flow of 236 cc/s. This is very high. With tube A and argon, a flow of 146 cc/s was used. It is interesting to note that this experiment was tried by Lecuiller et al (Ref. 6) (in non-streaming atmospheric air) with positive results for the reduction of ozone. In their case a narrew plexiglass tube was placed around the needle. The needle axis was along the discharge axis. The size of the tube opening is not given, but the nitrogen shrouding gas flow was 111 cc/ s. This is also an unusually high flow rate considering that the air is not flowing past the needle and so would not disturb the shrouding flow. These high flow results remain somewhat of a mystery. At flows of 71 cc/s in room air and a nitrogen shroud using tube B the N02 peak
was reduced by
30'/0,
the N03 peak by 7eP/o and the 03 peak 1;>y 81%. _ The02
peak remained unchanged. As the flow was increased to 246cc/s the Ü2 ion inc~eased. This can be seen in Figs. 6-17 to 6-18. If one uses the peak at 50 amu Ü2(H20) as a reference for the0.2
ion which is off sCale, then the increase inö2
is by a factor of 20. There are also large reductions in N03 and ~. The same effect was also noticed for argon using tube A (Figs. 6-19 to 6-~0). From theroom air data it may be seen that the N02 peak, and ions at mass 42 amu, 45
amu, 59 amy, 26 anru. and 64 amu increase. These ions are tentati vely identi-fied in order as: OCN-, HCOO-, CH3COO-, CN-, 04 or N02(H20). These ions are present as trace contaminants in room air. Their ionization involves the thermal process of proton abstraction by the
02
ion. This would indicate that electron thermalization is occurring. It is noticed in Figs. 6-1 and 6-2 that the N02 current is approximately 200xl03 counts per seconde With the glass tube on the needle this current drops to 6oxl03 counts per second, close to the value usually found in zero air.N0.2
increases to roughly 90-10Oxl03 counts per second when shrouding. This increase suggests that N02 is present in the air but shrouding does not make up the difference of 20xl03 counts per second, assuming that the value in zero air of 50-60xl03 counts per second is the production rate of N02. The big change which occurs when the tube is placed on the needle may indicate that the corona properties arebeing affected. For example, the glass may contain water or trace impurities on its surface and build up a substantial positive charge. Sparking to the glass was 'noticed if the needle was close. This may mean a negative space charge·could be drawn closer to the cathode causing the applied voltage to increase to maintain the same current. As seen in the previous section the 03' N02' C03 and N03 ions increase with a higher voltage. But this w~s due to their removal from the
discharge region &t a high rate. If this is not the case then the oxide current may decre&se as in the zero air experiment. Not only may the flux of neutrals entering the gap be reduced but also they may be subjected to depo~ulation processes.
The data for argon and tube A was taken on a different day. The N02 ion current was approximately 100 x 103 counts per second. When tube A was used a reduction of approximately 50 x 103 counts per second occurred but this was increased by shrouding back to its original value. This would indicate this glass tube affects the corona properties and the flux of neutrals into the gap, less than tube B. It also would indicate as before, nitrogen dioxide may be present in the room air and thermalization of the electrons is an effective way of detecting it. A simple measurement of the needle voltage would determine the effect of the tube and the shrouding gas on the corona properties. These are high flows and positive ions may be dispersed. If this was true a measurement of the corona current would show a decrease at a
constant supply voltage. It is unlikely positive space charge dispersion would account for the increased N02 signal through the reaction scheme suggested earlier for the generation of HN02.
111. CONCLUSIONS
In summary, electron thermalization with the addition of a shroud gas does seem to be occurring in both room air and zero air. Shrouding tube B was the best design since it was easy to manipulate on the
needle without interfering with the shrouding gas flow. If the degree of electron thermalization with shrouding is measured by the relative increase in the 02 ion and hydrates, then molecular nitrogen proved to be the most effective thermalization gas. Methane removed a greater percentage of the ozone derivatives than nitrogen but some ion loss occurred. In zero air the ions 0
3,
N02' N03,
and ~03 w~re redu~ed in intensity to less than 1%. I~ room air the ions 03, N03 and C03 decreased by approxima~ely 90%., The N02 ion was increased at best by approximately 100% indicating it is present in the room air. Electron thermalization by flowing a nonelectronegative gas around the needle tip permitsdetection of ambient air concentrations of N02. Since very high
shtou~ing gas flows were required to achieve this, greater than 200cc/s, it is questionable as to whether shrouding is a useful method for
detection of trace N02 or other traces. Perhaps if the needle axis were placed along the discharge axis then shrouding with a narrow tube
at very low flows could be possible.
Probably a more practical method for nitrogen dioxide analysis is removal of the background signal by withdrawal of the neutrals produced by the discharge. Tube B seems to be the best general design for this. Some reduction of the ozone derivatives was accomplished by enclosing'the needle with this tube. This demonstrates a loss of the neutrals, NO , NO and 0 3 produced near the needle tip. The actual opening ip Tabe ~ could be varied to achieve maximum withdrawal of the neutrals. Radial needle movement should also be combined with the suction method so as to eliminate interference by the tube on incoming
trace species and also to mln1mlZe dissociation of the traces by electron impact. In terms of nitrogen dioxide analysis radial needle movement in combination with suction is advantageous since off the discharge axis the neutral withdrawal should be facilitated due to the decreased importance of neutral transport by the fluid flow.
REFERENCES
1. Loeb, L. B., "Recent Advances in Basic Processes of Gaseous Electronics ", Vol. 1, (1978).
2. Ikute, N., Kondo, K., Proc. Int. Conf. Gas Discharges, 4th Swansea, Great Britain, I.E.E. Conf. Publ. (143), pp. 227-230 (1976).
3. Lama, W. L., Gall0, C. F., J. of Appl. Physics. Vol. 45 (11) 105 (1974). 4. Bastien, F., Haug. R., LecuilIer, M., J. Chim. Phys. 72 (1), 105 (1975). 5. LecuilIer, M., Julien, R., Pucheault, J., J. Chim. Phys. 1353 (1972). 6. Bastien, F., LecuilIer, M., J. Chim. Phys. 70 (11-12) 1692 (1973). 7. Sigmond, R. S., "Electrical Breakdown in Gases" editors J. M. Meek
and J. D. Craggs, pp. 319-385 (1978).
8. Loeb, L. B., "Electrical Coronas", pp. 299-402 (1965).
9. Gallimberti, J., Hepworth, J. K., Klewe, R. C., J. Phys. D. Appl. Phys. 7 881 (1914).
10. Khare, S. P., Kumar, A., J. Phys. B: 'Atom. Molec. 11(13) 2403 (1918). 11. Mazeau, J., Gresteau, F., Hall, R. I., Huete, A., J. Phys. B. Atom
Molec. Phys. 11 (18) 1978.
12. Goldman, M., Goldman, A., "Gaseous Electronics" editors M. N. Hirsh and H. J. Oskam, pp. 219-285 (1918).
13. French, J. B., Davidson, W. R., Thompson, B. A., Private Communication. 14. Ferguson, E. E., Fehsenfeld, F. C., Albritton, D. L., "Gas Phase Ion
Chemistry" , editor M. T. Bowers, Vol. 1, pp. 45-81 (1919).
15. Gardiner, P. S., Craggs, J. D., I.E.E. Conf. Publ. 5th Int. Conf. Gas Discharges. 81 (1918).
16. Janousek, B. K., Brauman, J. J., "Gas Phase Ion Molecule Chemistry" editor M. T. Bowers, Vol. 2, pp. 53-86 (1919)
11. Gurevich, D. B., POdmashenski, I.V. Optics and Spectroscopy, 15, 319 (1963). 18. Lacin, M., Korge, H., Kudu, K., J. Physique, Colloque C.1 1 C1-351 (1919) 19. Massey, H., "Negative Ions" (1916).
20. Tamaki, K., Yoshida, H., Katayama, T., Kaido, C., Nippon Kagaku Kaishi, 11, 1582 (1919).
21. Bartness, J. E., Mclver, R. T., "Gas Phase Ion Chemistry" , Vol. 2, editor M. T. Bowers, pp. 81-119 (1919).
22. Buckley, J. A., Ph.D. Thesis, UTIAS 1914. 23. Banks, D. M., Koekarts , G., "Aeronomy" (1913).
24. Fehsenfeld, F. C., Ferguson, E. E., J. Chem. Phys. 61(8), 3181 (1974) 25. Fehsenfeld, F. C., Ferguson, E. E., J. of Chem. Phys. 61(8), 3181,
(1974).
26. Smith, C. P., Lee, L. C., Cosby, P. C., J. Chem. Phys. 71 (11) (1979). 27. Lifshite, C., Wu, R. L. C., Tiernan, T.O., Terwi11iger, D. T.,
J. Chem. Phys. 68 (1) (1978~.
28. Ni1es, F. E., J. of Chem. Phys. 52(1) 408 (1969). 29. Lunt, R., Adv. Chem. Series 80 452 (1969).
30. Bes, R., J. Chim Phys. 75(3),312 (1978).
31. Stief, L. J., Payne, W. A., Lee, J. H., Michael, J. V., J. Chem. Phys. 70 (11) 5241 (1979).
32. Thomas, R. J., J. of Geophysical Research 83 (A2) 514 (1978) 33. Hidalgo, H., Crutzen, P. J., J. of Geophysica1 Research 82 (37)
58 33 (1977).
34. Yagi, S. Tanaka, M., J. Phys. D. Appl. Phys. 12 1509 (1979)
35. Huertus, M. L., Fontan, J., Gonzalez, J., Atmospheric Environment 12 2362 (1978)
36. Belova, V. M., Eremin, E. N., Ma1'tsev, A. N., Russian Journalof Physical Chemistry, 52 (7) 968 (1978).
TABLE 1: REACTIONS. THERMAL RATE CONSTANTS ANTI REFERENCES REACTION A. Neutral Reactions 1. 2. 3.
4.
5.6.
8.
9.
N+03 - -... NO+0 2 N+O 2 ---l.~ NO+O N0 2 +03 .. N03 +02 N+NO ---l"~ N +0 2 0+0 3 ---.~ 0 +0 2 2 0+N0 2 .~ NO+02 0+0 +M ~O +M 2 3 N20+O - -.. ~ N 2 +0 2 10. NO+0 3- - . " NO 2 +0 2 B. Charge Transfer 11. 12. 13. 14. 15. 16. 17. 0;+0 ---.. .. 0-+0 2 0-+0 - - -... 0-+0 3 3 0;+0 3 .. O2+0; OH-+O .O-+OH 3 3 O-+N0 2 --IJt"O+NO; O-+NO ~ . NO-+O 2 2 2 2 OH-+NO ~NO-+OH 2 2 C. Switching Reactions 18. 19. 21. 22. O-+N 0 - - . . . .. NO+NO-2 0;+C02 --".CO;+02 0-+NO - - - _ .. NO-+0 3 3o
+e - -... 0-+0 3 2 5(-16) 4.2(-17) 2.0(-14) 2.7(-11) 8.9(-15) 6.3(-12) 5.0(-33)*
5.8(-34)*
1.65(-14) 1. 5(-10) 8.0(-10) 6.0(-10) 9(-10) 1.2(-10) 1.2(-10) 1.0(-9 ) 2.5(-10) 5.5(-10) 1.1( -11) 1.0(-11 ) 9(-12) REFERENCE 31 32 33.34 3 32 34 4 33.34 33 14 14 14 14 27 27 1 19 14 14.1 19.1.4 14 Continued •••Table 1 - Continued REACTION 23. 24. 25.
26.
27.
28. 29. 0-+CH 4 ---...OH-+CH3 CO;+O • 0;+C0 2 CO; +N0 2 • NO; +C02 0l;+0 • 0;+0 0l;+C02 • COl;+02 COl; +0 .. CO; +0 2 CO-4+03 • O-+CO +0 3 2 2 30. NO; +0 3 • NO; +NO 31. CO;(H20)+NO~0;+C02+H20 33. 34. 35. 36.37.
38. 39. 40. 41. 42. COl;+H20 ~0;(H20)+C02 0;(H20)+C02~04+H20+02 0;(H20~+N02~0;(H20i+~0 k+l = n = 2,3,4 OH- (H20)n +C0 2..rICO; (H20)k + H20 k+1= n = 2,3,4 0;(H20)+C02~0;+02+H20 0;(H20)+ 0~;(H20)+02 0;(H20)+NO~;(NO)+H20 O-+H 0 ---~ •• OH-+OH 2 0- (H 20 )+O~ 0; +H20 0-(H20)+H20~(OH-)(OH) D. Association Detachment 43. 0-+N --...., ... NO+e 44. 0 +NO - -•• NO +e 2 O;+N ----•• NO +e 2o
+0 - -•• , 0 +e 2 0-+0 2 - -... 0 +e 3 NO+O 45. 46.47.
48. 0-+N
---I..
N0+e-. 25ev8(-11) 5.5(-10) 2(-10) 5.5(-10) 4.3(-10) 4.8(-11) 1.3(-10) 1.2(-10)
7(-12)
1. 5 (-9) 2.5(10) 5.8(~10) 9(-10) 6(-10) 3.5(-10) 2.3(-10) 3(-10) 6(-13) <l{-11) > 1(-11) 2.2(-10) 5(-10) 5(-10) 1.9(-10) 3.3(-10) <1(-12) REFERENCE 14 14 14 14 14,4 14 14 14 14 35 35 35 25 25 25 25 25 2526
25 19 4 19 4 19 1Table 1 - Concluded
REACTION k (cm /mol/s) 3 . REFERENCE
E. Attachment 49. e+0 2+M ~ O;+M M
=
02 19(-30) 35 M=
N2 1.0( -31· ) 35 M=
H20 1. 4( -29) 35 M=
C02 6.1(-31) 35F. Three Body Association
50. 0;+2°2
.
..
°4+°2 5.1(-31) 35 51. 0-+2C0 2..
CO;+C02 9(-30) 19 52. 0;+C02 +02 ~ C0 4 +02 4.7(-29) 35 53. 0-+N+M..
NO-+M 1. O( -29) 4 2 2 54. O-+NO+M .. NO;+M 1. O( -29) 4 55. CO;+H 2O+M - . CO; H20 + M 1.0(-28) 35 56. O-+H 0+0 2 2 .. 0;(H2O) 1.6(-28) 35 57. O-+H 0+0 - . . . 2 2 0;(H2O)+02 1.3(-28) 35,26 58. 0-+H 0+0 ---.. 3 2 2 0;(H2O)+02 2.7(-28) 35 59. OH-+H 0+0 ----. 2 2 OH-(H2O)+02 2.5(-28) 35,26 60. OH-+CO +0 ~OH-(CO )+0 2 2 2 2 7.6(-28) 35,26,14 61. 0;(H20)+H20+02~0;(H20)2+02 5.4(-28) 35 62. 0;(H20)2+H20+0~;(H20)3+02 2.1(-28) 35 63. 0;(H20)3+H20+0~;(H20)4+02 1. O( -28) 35 64. NO;+H 2O+02 ... NO; (H20 )+02 ' 1.6(-28)The number in brackets denotes the power to which 10 is raised to.
*
3 body rate constant cm6/mol?/sMass(amu) 16 17 26 32 34 35 37 42 43 45 46 48 50 52 53 55 59 60 61 62 64 66 68 70 71 72 73 76 77 78 79 TABLE 11
Tenative Ion Identification
Structure 0- OH- CN-O 2 -160180, 0-(H20) 35c1, OH-(H20 ) 37Cl OCN- HCOO-N02 -°3 0; (H20) 16080(H20), 0-(H20 )2 35C1 (H20 ), OH(H20 )2 37/C1(H20) CH3COO-CO; HCO; NO;
