Electron scattering on molecules - Partial (and Total) Cross Sections: Search of Uncertainties and Errors in Experimental Procedures

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Electron scattering on molecules - Partial (and Total) Cross Sections:

Search of Uncertainties and Errors in Experimental Procedures

G.P. Karwasz, K. Fedus

Nicolaus Copernicus University, Toruń, Poland

IAEA Meeting, Wien, 19.12.2016

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2. Partial cross sections:

elastic scattering e+A →e+A

rotational excitation e+CH₄ (J=0) → e+CH₄ (J=2) vibrational excitation e+AB(v=0) → e+AB(v>0) electron attachment (dissociative) e+AB → A^- + B

electronic excitation e+A →e+A^* emission lines: A^* → A + hv

neutral dissociation e+AB → A + B + e

emisison from dissociation e + AB → A^* + B + e + hv ionization e+A →A⁺+2e

dissociative ionization e+AB → A + B⁺+ 2°

ionization into excited states e + A → (A⁺)^* + 2e

1. Total cross section

Data needed:

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1. Plasma modelling (electrical discharges, „economic”

ligth sources);

(plasma temperature in Ar discharges, 0.3 eV is determined by minimum in MT cross section )

2. Plasma etching and deposition

(energy of etching radicals, ionization level)

3. Chemical reactions in plasmas (ionization, dissociation)

4. Radiation damage in materials and biological tissues 5. Thermonuclear fusion reactors

Data needed in:

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Plasma temperature ← integral cross sections

0,1 1 10

1 10

e^- + He e^- + Ne e^- + Ar e^- + Kr

Total cross section (10-20 m2 )

Electron energy (eV)

V. Godyak, Sendai 2006

Ramsauer minimum

(zero in s-wave)

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Radiation damage in biological tissues

M. C. Fuss, ... G. Garcia Chem. Phys. Lett. 486 (2010) 110

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¿ITER: electron T and power irradiated

Guillemaut et al. Nucl.Fusion (2014) Power irradiated (0.5-1.5 MW) simulation:

JET-C <10% JET-ILW factor 3!

Electron temperature (and density) during three points of density ramp

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Experimental methods: total

attenuation method I = I₀ exp(-σnL) precision <5%

H. Nishimura et al., J.Phys. Soc. Japan 72 (2003) 1080

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attenuation method I = I₀ exp(-σnL) precision <5%

Mi-Young Song, Jung-Sik Yoon, Hyuck Cho, Yukikazu Itikawa, Grzegorz P. Karwasz · Viatcheslav Kokoouline, Yoshiharu Nakamura, Jonathan Tennyson, J. Phys. Chem. Ref. Data, 44 (2015) 023101

Experimental methods: total

Agreement generally within ±5%

Apart from high E

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Total @ high energies: Born-Bethe fit

Fig.4. Born-Bethe fit (σ/a_o²) (E/R) = A + B ln (E/R) to TCS from Ariysainghe: A=52.31±17.3, B=232.2±8.6 where Rydberg constant is R=13.6 eV and the cross sections is expressed in atomic units a₀² =0.28x10^-20m²

C₂H₂

σ(E) = A + B lnE

„In the high energy limit present (GK, Zecca) measurements

are affected by angular resolution error. In order to evaluate it, differential cross sections at low angles would be needed. A rough evaluation from Born approximation for the elastic channel gives an error of a few percent. Note that the error in TCS can be higher, as Trento apparatus does not perform discrimination against inelastically forward-scattered electrons.

CH₄

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Total: experiment & theory (NF

₃

)

B. Goswami et al. PRA 88 (2013) 032707 (NF₃)

NF₃

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Experimental methods: elastic

I. Linert, B. Mielewska, G. King, and M. Zubek, PRA (2006)

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Experimental methods: excitation (electronic, vibrational)

Experiments by:

I. Linert, M. Zubek (Gdansk) J. Phys. B 39 (2006) M. Khakoo et al. (Fullerton California)

M. Allan (Freiburg University)

e

^-

+ O

₂

(v=0) – e

^-

+ O

₂

(v=0, 1, 2, etc.)

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Experimental methods: ionization

R. Basner, M. Schmidt, K. Becker, Int. J. Mass Spectr. 233 (2004) 25

WF₆→

WF₅⁺ > WF₂⁺>

WF₃⁺ ≈ WF₄⁺

Accuracy: ±15%

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



 

 



 



0

0 2

/

1

( )

) ( 3

2 dE

dE E df

E E N

eF w m



m





 

 



 

0

0 2

/ 1

) ) (

( 3

1 2 f E dE

E E N

D m

m

T



) , ( )

, ( )

, ( -

) ,

(

₂

2 2

2

t z n

D t

y n t

x n D

t z n

w t

t n

^e

r

^e

r

^T ^e

r

^e

r

^L ^e

r



 

 

 







 



 



 



Diffusion coefficients → electronic

distribution function n

_e

(r, v, t)

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Example: oxygen O

₂

• Rotational and vibrational

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Oxygen – total cross section

0.1 1 10 100

0 5 10 15

Szmytkowski 96 Zecca TN Zecca GD Dababneh 88 Kanik 92 Ramsuaer 30 Buckman 99 Subramanian

Total cross section (10-16 cm2

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Example: oxygen O

₂

• Electronic – not justified (a

¹

Δ is resonant)

A. Zecca, G. Karwasz, R. S. Brusa, Riv. Nuovo Cimento Vol. 19, No. 3 (1996)

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Electronic excitation – dipole allowed and forbidden in H

₂

10 100

0.1 1

b ³⁺_u

Nishimura Khakoo Hall Khakoo 94 Fliflet

Integral cross section (10-16 cm2 )

Energy (eV)

10 100

0.1 1

B ¹⁺_u

Khakoo Srivastava Shemansky Fliflet

Energy (eV)

10 100

0.1 1

C ¹_u

Khakoo Shemansky Mu-Tao

Energy (eV)

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Hydrogen – a complete set

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Hydrogen

– a complete set

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Hydrogen – a complete set

Mark C. Zammit, Jeremy S. Savage, Dmitry V. Fursa, and Igor Bray Phys. Rev. Lett. 116, 233201

http://journals.aps.org/prl/abstract/10.1103/PhysRevLett.116.233201

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Hydrogen – a complete set

Jung-Sik Yoona), Mi-Young Song, Jeong-Min Han, Sung Ha Hwang, Won-Seok Chang, and BongJu Lee Journal of Physical and Chemical Reference Data >

Volume 37, Issue 2 >

10.1063/1.2838023

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Electronic excitation – dipole allowed and forbidden in H

₂

10 100

0.1 1

b ³⁺_u

Nishimura Khakoo Hall Khakoo 94 Fliflet

Energy (eV) ¹⁰ ¹⁰⁰

0.1 1

B ¹⁺_u

Khakoo Srivastava Shemansky Fliflet

Energy (eV)

10 100

0.1 1

C ¹_u

Khakoo Shemansky Mu-Tao

Energy (eV)

Zecca, Karwasz, Brusa, Nuovo Cimento 1996

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Hydrogen – electronic excitation (modelling)

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Hydrogen – electronic excitation (2010)

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Resonances: „Huston...” (N

₂

O)

0.1 1 10 100

0 5 10 15 20 25 30 35

40 Szmytkowski 89

Szmytkowski 96 Kwan 84

Kitajima Ramsauer

Total cross section (10-16 cm2 )

SE SEP CI

Sarpal et al. 1996 Sarpal et al. 1996

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0.1 1 10 100 0

5 10 15 20 25 30 35

40 Szmytkowski 89

Szmytkowski 96 Kwan 84

Kitajima Ramsauer

Total cross section (10-16 cm2 )

Morgan et al. 1997 Morgan et al. 1997

SEP SE

Resonances: ¿elastic/ vibrational (N

₂

O)

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Dissociation into neutrals (H

₂

O)

Herb and McConkey Herb and McConkey

Laser-induced fluorescence

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Dissociation into neutrals (N

₂

O)

LeClair and McConkey JCP 99 (1993) 4566

N

₂

O → O(

¹

S

₀

)

XeO* excimer decay

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Dissociation into neutrals (CF

₄

)

Two electron beams: dissociation & ionization

Nakano and Sugai, Jpn. J. Appl. Phys. 31 (1992) 2919

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Dissociation into neutrals (CF

₄

, CH

₃

F…)

Motlagh and Moore JCP 109 (1988) 432 Motlagh and Moore JCP 109 (1988) 432

„Volatile organotellurides”

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Dissociation into neutrals (CF

₃

COOH)

Thermal desorption

Reactions in nanofilms of trifluoroacetic acid (CF₃COOH) driven by low energy electrons, M. Orzol, T. Sedlacko, R. Balog, J. Langer, G. P. Karwasz, E. Illenberger, A. Lafosse, M. Bertin, A. Domaracka, R. Azria, Int. J. Mass Spectr. 254 (2006) 63

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Polar molecules (HCN)

A. G. Sanz, Applied Radiation and Isotopes 83 (2014) 57–67

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Polar molecules (HCN)

A. G. Sanz, Applied Radiation and Isotopes 83 (2014) 57–67

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Polar molecules (e ⁺ /e ^- + HCOH)

Independent atom model-screened additivity rule / Schwinger multichannel

A Zecca, E Trainotti, L Chiari, G García, F Blanco, M H F Bettega, M T do N Varella, M A P Lima and M J Brunger Journal of Physics B: Atomic, Molecular and Optical Physics, Volume 44, Number 19

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Polar molecules (e ⁺ /e ^- + HCOH)

Theory: Independent atom model-screened additivity rule / Schwinger multichannel Experiment: weakly (9G) magnetically guided positron beam/ W monocrystal moderator

A Zecca, E Trainotti, L Chiari, G García, F Blanco, M H F Bettega, M T do N Varella, M A P Lima and M J Brunger Journal of Physics B: Atomic, Molecular and Optical Physics, Volume 44, Number 19

„in good qualitative agreement with our measured data”

Experimental (¿possible?) errors:

- Declared energy resolution 260 meV ↔

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Polar molecules (e ⁺ + H ₂ O)

NJP 11 (2009)

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Polar molecules: e ^- + H ₂ O

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Check of congruence: CF

₄

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Check of congruence: NH

₃

Really poor agreement...

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Check of congruence: CHF

₃

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Ionization

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Conclusions

• Quite few laboratories continue to produce partial cross sections

• Some new labs yield very competitive (and promising) measurements

• Electronic excitation is the main chalenge, both to experiment and theory

• Extension of BEB ionization to partial ionizations would be

„breaking” – correlation measurements seem to allow it but direct and secondary ionization (i.e. energy spectra) would be important

• Vibrational excitation is poorly understood – both at thresholds (peaks or not?) and at resonances: agreement with swarms is only apparent

• Rotational excitation, even if (maybe) not important for plasma temperature, can be decisive in electron slowing down, and (in biological tissues), in „brougthing” them to energies matching zero- energy alactron attachment resonances.

• Comparative works are important, as this is the way to identify reasons for serious disagreements in some tagets (including positron scattering)