new collision data for h/h 2 and c x h y databases
DESCRIPTION
New Collision Data for H/H 2 and C x H y Databases. R.K.Janev Macedonian Academy of Sciences and Arts, Skopje, Macedonia. Scope:. Resonant vibrational excitation and dissociative attachment in e-H 2 in 11-14 eV region; - PowerPoint PPT PresentationTRANSCRIPT
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)