New Collision Data for H/H2 and CxHy Databases

R.K.Janev

Macedonian Academy of Sciences and Arts, Skopje, Macedonia

Scope:

• Resonant vibrational excitation and dissociative attachment in e-H2 in 11-14 eV region;

• Mutual neutralization in slow collisions of H- with H2

+ and H3+ ions;

• Electron impact excitation of X→ A and X→B transitions in CH

• Dissociative excitation and ionization in e + CHy

+collisions

1. RVE and DEA in e+H2 in 11-14 eV collisions

• Processes:

e + H2(X1Σg+;v=0) → H2

-(2Σg+) →

→ H2(X1Σg+;v) + e (RVE)

→ H- + H(n=2) (DEA)

• Theoretical approach:

- Resonance theory

- Local complex potential approximation

Elements of calculations

2

2

( )( ),

. 0

( )

( )

[ ( , )]

( , ) ( )

( ) ( , )

( , ) ( ),

( ; ) ( )

. .

N el

tel el e e t

H ed v J

v J

d d

H evJ

T H q R E

H q R H T V q

d f q R

q R R

q R R

Schroed Eq

LCA

→Non-local integro-differential Eq. for ζ(R)

In the local complex potential approximation this equation becomes (after separating the angular part):

2( )

,2 2

2

1 ( 1)( ) ( ) ( ) ( ) ( )

2 2 2

1( ) ( )

2

i v J

d J JV R i R E R F R R

M dR MR

F R R

H2¯ energy parameters

V ¯(R) : H2¯ (2Σg

+) potential energy curve

Г(R) : decay width of H2¯ (2Σg

+) state

Information on V ¯(R) and Г(R) from Stibbe and Tennyson (1998;J.Phys.B) with suitable extrapolations

RVE cross sections

Chang, 1977; Herzenberg, 1979

2

( ) ( )

1( ) (cos )

4

i f

i f

resresv v l

v v

l

L LlL

dE g

d

g A P

2. Dissociative electron attachment

Equations for ζi(R) in the LCA approximation are the same as in the RVE case

Cross section:

222

lim ( )DEA i Ri

KR

k M

3.Mutual neutralization in slow H2+,H3

+ - H- collisions

a) H2+(1sσg) +H-(1s2)→H2(1sσg;nλσg)+H(1s)

Radial coupling selection rule:Overall symmetry of initial and final states in reaction a)

should be the same: → 1,3Σg

+ final states of H2

Strong radial coupling of initial (ionic) and final (covalent) states exists only for exothermic channels: → n ≤ 3

→Final H2 states: X,EF,GK,HH (singl.) , a, h, g (tripl.)

Schematic potential energy diagram (at large distances)

Theoretical model

• Multichannel Landau-Zener model

(probability flux accumulation along various reaction paths for a given exit channel)

• Landau-Zener two-state transition probability

in the strong interaction region (around Rx)

,

22

11

,

2 ( )exp , ( )

( )

1exp( )

2

x k

ick

R R R

ic i c S

H Rp F R R

v F R

H A A D R R

H3+ + H-

• D3h symmetry for H3+ and H3

* states

• Initial state: H3+[(1sa1

’)2 A1’] + H-(1s2) (i)

• Final states with same symmetry as (i):

• H3[(1sa1’2 nla1

’)A1’] + H(1s)

• Reaction exothermicity condition selects the first four A1

’ states of H3*

Computational method

• Multichannel Landau-Zener (LZ) model

• LZ two-state transition probability

• Asymptotically exact ionic-covalent electron exchange interaction

Radiative and predissociation decay of H3

* states

• H3*(nl;A1

’)→ (intermediary state)→

… H3[(1sa1’)2(2pe’)E’]→H2(X1Σg+) + H(1s)

→3H(1s)

(Ground state of H3 is degenerate in the FC region of H3+

with two energy branches at large R; Yahn-Teller system)

4. Dissociative excitation and ionization of CDy

+ by e-impact

Processes:

e + CDy+ → e + I+ + neutrals (DE) (y=1-4)

e + CDy+ → 2e + I1

+ +I2+ + neutrals (DI)

• Recent total cross section measurements for specific ion production, σtot(DE+DI), and also σtot(DI) for D+ production;

• Mesurements of total KER at a few energies

• (Louvain-la-Neuve group; P.Defrance)

Separation of channels

• Determine channel thresholds from theoretical dissociation energies and observed KER spectra

• Determine cross section points by integrating the KER peaks for a given channel at the corresponding energy

• Use the inverse proportionality of cross section maximum with the threshold energy

• Use the absolutely measured ionization cross section for H+ production and empirical scaling rule for the linearity of DE+ and DI+ fragments with the number of D atoms in CDy

+ at high energies

Status:

For all CDy+ ions DE+ and DI+ channels have been

separated

For each of the DE+ or DI+ ion production channels the neutral fragmentation sub-channels have also been separated

All the DE+ and DI+ channel cross sections have been fitted to (relatively) simple analytic fit functions

5. e-impact excitation of X→A and X→B transitions of CH

• Computational method:

- Born approximation for dynamics - Ab initio calculation of dipole moments

• vi-vf resolved transitions

• Predissociation included

• Calculations of transitions to higher states also planned

Bethe-Born formula

2 2max0. 0, 0

min

0,1/ 2max ,0 min 1/ 2

4( ) ln ( )

3

2(2 ) ,

2

n n

nb

KD R a

E K

EK E K

E

Contributors:

• R. Celiberto (Politechnico di Bari)

• J. Wadehra (Wayne Univ., Detroit)

• P. Defrance, J. Lecointre, et al.

(Univ. Catholique de Louvain-la-Neuve)

• J.G.Wang, C.L.Liu (IAPCM, Beijing)