electron impact ionization of selected hydrocarbon molecules

Electron Impact Ionization of selected hydrocarbon molecules

Štefan Matejčík

Comenius UniversityBratislava,Slovakia

Coworkers

Dušan Kubala Jaroslav Kočíšek Peter Papp Pavel Mach Jan Urban

Stephan Denifl Fabio Zappa

Univ. Innsbruck

Electron impact ionisation - EII e + M → M+ + 2e

e + M → X+ + (M-X) + 2e

Appearance energies

Partial cross sections for EII

Crossed beams apparatus

low Tg

high Tg

E

σ

Electron impact ionization

Molecules studied in 2007 and 2008 Experiment

C2D6

CH3D

CD4

C3H8

C3H6D2

Theory BenHm

0 10 20 30 40 50 60 70 80 90 100 110 120 130 1400

1

2

3

10.09.2007

C

ross

se

ctio

n (

10-1

6 cm

2 )

Electron energy (eV)

Ar+ [10-16 cm2] Ne+ [10-16 cm2] Argon (nomalized) Ne (normalized)

Ar and Ne cross sections

R. Rejoub, B.G. Lindsay, R.F. Stebbings, Phys. Rev. A, 65 (2002) 042713.

Cross section EII C2D6 low temperature

0 10 20 30 40 50 60 70 80 90 100 110 120 130 140

0

1

2

3

4

5

6

T = 100°C

C2D

4

+ (m/z=32)

C2D

6

+ (m/z=36)

C2D

3

+ (m/z=30)

C2D

5

+ (m/z=34)

C2D

2

+ (m/z=28)

C

ross

-sec

tion

[10-1

6 cm2 ]

Electron energy [eV]

Cross section EII C2D6 high temperature

0 20 40 60 80 100 120 140

0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

4.0

4.5

5.0

5.5

6.0

6.5

7.0

C2D

4

+ (m/z=32)

C2D

6

+ (m/z=36)

C2D

3

+ (m/z=30)

C2D

5

+ (m/z=34)

C2D

2

+ (m/z=28)

Cro

ss-s

ect

ion

[10

-16cm

2]


T = 410°C

Comparison total cs C2D6

0 20 40 60 80 100 120 140

0

2

4

6

8

10

12

C

ross

se

ctio

n [1

0-16cm

2]


TOTALat100 TOTALat410

Comparison partial cs C2D6

0 20 40 60 80 100 120 140

0.0

0.5

1.0

1.5

2.0

cro

ss s

ect

ion

[10

-16cm

2]


C2D6at100 C2D6at410

(C2D

6)+/C

2D

6


0 20 40 60 80 100 120 140

0.0

0.2

0.4

0.6

0.8

1.0

1.2

C

ross

se

ctio

n [1

0-16cm

2]


C2D5at100 C2D5at410

(C2D

5)+/C

2D

6


0 20 40 60 80 100 120 140

0

1

2

3

4

5

6

7

C

ross

se

ctio

n [1

0-16cm

2]


C2D4at100 C2D4at410

(C2D

4)+/C

2D

6


0 20 40 60 80 100 120 140

0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

C

ross

se

ctio

n [1

0-1

6cm

2]


C2D3at100 C2D3at410

(C2D

3)+/C

2D

6


0 20 40 60 80 100 120 140

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

C

ross

se

ctio

n [1

0-1

6cm

2]


C2D2at100 C2D2at410

(C2D

2)+/C

2D

6

Threshold cross sections C2D6

10 11 12 13 14 15 16 17 18 191E-5

1E-4

1E-3

0.01

0.1

1

C

ross

se

ctio

n [1

0-1

6cm

2]


IE = 11.72 eV

(C2D

6)+/C

2D

6

Threshold cross sections C2D6

10 11 12 13 14 15 16 17 18 191E-5

1E-4

1E-3

0.01

0.1

C

ross

se

ctio

n [1

0-1

6cm

2]


AE = 12.64 eV

(C2D

5)+/C

2D

6

Ion Mass (amu) AE (100°C) AE (420°C)

C2D6+ 36 11.72 11.48

C2D5+ 34 12.64 12.33

C2D4+ 32 12.00 11.54

C2D3+ 30 14.92 14.94

C2D2+ 28 14.95 14.42

CD+ 16 22.25 22.17

C2D5++ 17 35.71 34.12

CD2+ 18 15.69 15.66

C2+ 24 23.54

28.5423.1728.11

C2D+ 26 25.22 24.84

e + C2H6 Experiment Theory

AE [eV]293 K

Thermochemistry[eV]

G3B3AIE [eV]

C2H6+ 11.46±0.04 11.55

C2H5+ + H-

C2H5+ + H

12.06±0.0612.7±0.1

11.7212.47±0.03

12.0312.79

C2H4+ + H2 11.90±0.04 11.92±0.0006 11.93

C2H3+ + H + H2 15.02±0.1 14.47±0.46 14.83

C2H2++2H2 15.02±0.1 14.61±0.01 14.61

C2H++2H2+H

C2H++H2+3H 25.7±0.3

20.5±0.1525.1±0.15

21.6526.12

C2+ + 3H2 22.6±0.3 20.95±0.3 21.73

EII to CD4 cross sections

0 20 40 60 80 100 120 1401E-21

1E-20

1E-19

1E-18

1E-17

1E-16

Cro

ss s

ect

ion

(cm

2 )


Tarnovsky et al.

CD4

+

CD3

+

CD2

+

CD+

26°C

e + CD4 -->

CD4

+

CD3

+

CD2

+

CD+

C+

Tarnovsky et al. J. Phys. B: At. Mol. Opt. Phys. 29 (1996) 139

0 20 40 60 80 100 120 140

0.0

5.0x10-17

1.0x10-16

1.5x10-16

2.0x10-16

Cro

ss s

ect

ion

(cm

2)


CD4

+/CD4

303 K 683 K Tarnovsky et al.

CD4+/CD4

CD4+/CD4

6 8 10 12 14 16 18 20

0.0

5.0x10-18

1.0x10-17

1.5x10-17

2.0x10-17

Cro

ss s

ect

ion

(cm

2)


CD4

+/CD4


CD3+/CD4

0 20 40 60 80 100 120 140 160 180 200 220

0.0

5.0x10-17

1.0x10-16

1.5x10-16

Cro

ss s

ect

ion

(cm

2 )

CD3

+/CD4



CD2+/CD4

0 20 40 60 80 100 120 140 160 180 200 220

0.0

5.0x10-18

1.0x10-17

1.5x10-17

2.0x10-17

2.5x10-17

3.0x10-17

3.5x10-17

CD2

+/CD4


Cro

ss s

ect

ion

(cm

2)


CD+/CD4

0 20 40 60 80 100 120 140

0.0

2.0x10-18

4.0x10-18

6.0x10-18

8.0x10-18

1.0x10-17

1.2x10-17

1.4x10-17

Cro

ss s

ect

ion

(cm

2 )

CD+/CD4



Tarnovsky et al. J. Phys. B: At. Mol. Opt. Phys. 29 (1996) 139

EII to CH3D cs

0 20 40 60 80 100 120 140

10-20

10-19

10-18

10-17

10-16

Cro

ss s

ectio

n (

cm2)

E (eV)

CH3D300 CH2D300 CHDCH3m300 CDCH2 C CH3Dm683 CH2Dm683 CHDCH3m683 CDCH2m683 Cm683

EII to C3H8

0 20 40 60 80 100 120 1401E-3

0.01

0.1

1

100°C

e + C3H8 C

ross

Sec

tion

(in 1

0-16 cm

2 )


C2H

5

+

C2H

4

+

C3H

8

+

C2H

3

+

C2H

2

+

C3H

7

+

C3H

3

+

C3H

2

+

C3H

5

+

EII to C3H8

0 20 40 60 80 100 120 1401E-3

0.01

0.1

1

Cro

ss S

ectio

n (in

10-1

6 cm2 )

Electron Energy (in eV)

C3H

8

+

C3H

7

+

C3H

5

+

C3H

3

+

C2H

5

+

C2H

4

+

C2H

3

+

C3H

3

+

C2H

2

+

e + C3H

8

410°C

EII to C3H6D2

10.2 10.4 10.6 10.8 11.0 11.2 11.4 11.6

0

100

200

300

400 Fit amu46

Ion

yie

ld (

arb

. un

its)

Electron energy eV

10.8eV11.1eV

En

erg

y

Q

M+

M

VIE

En

erg

y

Q

M+

M

VIE

EII to C3H6D2

e + M → C3H8

AE (eV)290 K

C3H6D2

AE (eV)

(C3H8)+

v(C3H6D2)+

10.51 ± 0.0510.96 ± 0.05

10.81 ± 0.0511.13 ± 0.05

Kim-s BEB (binary encounter Bethe) theory [W. Hwang, Y.-K. Kim, M. E. Rudd, J. Chem. Phys. 104, 2956 (1996)],

HF/6-31++G(2df,2pd) orbital kinetic energies OVGF/6-31++G(2df,2pd) ionization potentials

for ionization from valence orbitals For core orbitals IP the HF values were used

(their contribution to total cross section in studied region is very small).

Ionization cross sections calculations

Ionization potential of Be5Hn clusters as a function of “n”.

5.5

6.5

7.5

8.5

9.5

10.5

11.5

12.5

Be

5H

10

B5

H8

Be

5H

6

Be

5H

4

Be

5H

3

Be

5H

2

Be

5H

1

IP [

eV]

Most stable cluster of given stechiometry.

Method:

MP4(SDTQ)/6-31++G(2df,2pd)

Geometry:

MP2/6-31++G(2df,2pd)

Total ionization cross sections for Be5Hn clusters

10 100 10000

2

4

6

8

10

12

14

16

18cr

oss

se

ctio

n [A

2]

Energy [eV]

Be5H

10

Be5H

4

Be5H

Increasing hydrogen content in mixed clusters increases IP and decrease cross section for ionization

Conclusions Measured partial cs for EII to

CH3D CD4

C2D6

C3H8

Appearance energy – C3H6D2

Calculated ionization energies Be5Hn

EII total cross sections Be5Hn

electron impact ionization of selected hydrocarbon molecules

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