Post on 22-Feb-2016
description
Martin ČížekCharles University, Prague
Non-Local Nuclear Dynamics
Dedicated to Wolfgang Domcke and Jiří Horáček
1348
Studied processes:
AB(v) + e- AB(v’ v) + e- (VE) AB(v) + e- A + B- (DA)
A + B- AB(v) + e- (AD)
AB(v) + e- (AB)- A + B-
Outline of Theory
Review: W. Domcke, Phys. Rep. 208 (1991) 97
http://utf.mff.cuni.cz/~cizek/
• Fixed nuclei calculation as a first step.
• Fano-Feshbach projection to get the electronic basis.
• Known analytic properties of matrix elements (threshold expansions) used to construct proper model.
• Nuclear dynamics solved assuming diabaticity of basis.
Electronic structure for fixed-R
A+ + B-
A + B
Negative ion system (HCl)- Two state Landau-Zener model
H + Cl-
HCl + e-
Main idea behind the theoretical approach (O’Malley 1966):
Selection of proper diabatic electronic basis set consisting of anionic discrete state and (modified) electron scattering continuum
Extraction of resonance from the continuum
Essence of the method:
Selection of a square integrable function (discrete state) describing approximately the resonance and solution of scattering problem with additional constraint (orthogonality to the discrete state)
It is show that sharp resonance structures are removed from continuum with sensitive choice of discrete state
Example:
Scattering of particle from spherical delta-shell. Discrete states – bound states in box with the same size as the shell.
Discrete state … Continuum …
Coupling
Diabaticity of the basis:
Hamiltonian in the basis:
Final diabatic basis set),( rRd
),( rR
)(RVH ddeld
)'())(( 0' RVH el
)(RVH deld
0),( ,0),(
rR
RrR
R d
dVVVVTH dddddddN )( *0
00)(
0)(0
0)(0
00)(
*0
0 RV
RV
TRV
RVT
VHd
d
N
dN
Nonlocal vibrational dynamics in (AB)- state
• Expansion of wave function),()( ),()(),( rRRdrRRrR d
• Projection Schrödinger equation on basis
)( )()( )(
)( )( )( )( 0),()(*
0 RRVRRVTERRVdRRVTErRHE
dN
ddN
• Formal solution of second line for (R) into first line
)'(')( )',,( where
0)( )',,(')( *1
0 RVRiVTERRVdRREF
RRREFdRRVTE
dNd
dN
• The similar procedure for Lippmann-Schwinger equation yields:
)AB(vefor )(BAfor
e wher,)( -0
-1
ivd
iKR
dNii
VEGe
FViTE
wherewhere
Threshold behaviorThreshold behavior
)()(2
)1(21
22
2
RERVR
JJR dd
0)'()'()',,(')( RRRREEfdRR dJv
Jv
v
Jv
Equation of motion for nuclei
)'()()0'(')',,( *''
1 RVRVidRRf dd
)(~)(RVd
210 :scattering dipole
21 :scattering wave-s
23 :scattering wave-p
Nonlocal resonance modelDynamics is fully determined by knowledge of the functions
V0(R), Vd(R), Vd(R)
)'/(),'( '..1),( |)(|2),( 2
RdpvRRVR d
')(2
)()',,(0
RiRRREF VTE N
It is convenient to define:
Then it is)(
2)( RiR
Summary – our procedure
• Model parameters V0(R), Vd(R) and Vdε(R) found from Fano-Feshbach or fit for fixed-nuclei
• Analytic fit made for R and e-dependencies in Vdε(R) to be able to perform the transform
and efficient potential evaluation• Nuclear dynamics is solved for ψd(R) component• Cross sections or other interesting quantities are
evaluated
)'()()0'(')',,( *''
1 RVRVidRRf dd
Results HCl(v) + e- HCl(v’) + e- (VE)
Results – vibrational excitation in e- + HCl
Integral cross section. Theory versus measurement of Rohr, Linder (1975) and Ehrhardt (1989)
Differential cross section. Measurement of Schafer and Allan (1991)
Results – vibrational excitation in e- + HCl
Elastic cross section. Theory -- resonant contribution (top) versus measurement of Allan 2000 (bottom)
Vibrational excitation 0->1. Theory (top) versus measurement of Allan 2000 (bottom)
VE in e-+H2
Interpretation of boomerang oscillations
• Dashed line = neutral molecule potential
• Solid line = negative ion – discrete state potential
• Circles = ab initio data for molecular anion
Boomerang oscillations:interference of direct process and reflection from long rangepart of anion potential
Results HBr(v) + e- H + Br- (DA)
Results – DA to HBr and DBr
Comparison with measurement of Sergenton and Allan 2001
Results
H2 + e- ↔ H2- ↔ H-+H
M. Čížek, J. Horáček, W. Domcke, J. Phys. B 31 (1998) 2571
H+H- → e- + H2
M. Čížek, J. Horáček, W. Domcke, J. Phys. B 31 (1998) 2571
Potentials for J=0 Potential Vad(R) for nonzero J
The Origin of the Resonances
Cross section
AU
TOD
ETA
CH
MET
Resonant tunneling wave function En
ergy
)(Rd
Vad(R) + J(J+1)/2μR2
Elastic cross section for e- + H2 (J=21, v=2)
Γ0=2.7×10-4eV
Elastic cross section for e- + H2 (J=25, v=1)
Γ0=2.7×10-9eV
Γ1=1.9×10-6eV
Table I: Parameters of H2- states
J Eres (relative to DA) τ
21 -136 meV 2.4 ps
22 -105 meV 12 ps
23 -75 meV 0.11 ns
24 -47 meV 0.9 ns
25 -20 meV 12 ns
26 5 meV 0.52 μs
27 28 meV 2 ns
Table II: Parameters of D2- states
J Eres(relative to DA) τ
31 -118 meV 0.13 ns
32 -97 meV 0.70 ns
33 -76 meV 6 ns
34 -55 meV 39 ns
35 -35 meV 0.51 μs
36 -16 meV 5.7 μs
37 2 meV 14 μs
38 19 meV 7.2 μs
39 34 meV 41 ps