Åsa Larson Ann E. Orel

Transcription

1 Charge recombination reactions involving the H 2 and HeH systems Åsa Larson Ann E. Orel 3 rd meeting of the CRP on Hydrogen and Helium, IAEA March

2 Charge recombination reactions + - A + + B - AB * A + B Mutual neuralization Fully quantum ab intio studies Total and differential cross sections Isotope effects Role of autoionization Role of rotational couplings

3 Charge recombination reactions e - + AB + + e - AB * A + B Dissociative recombination What we are aiming for Success of a simplified model?

4 Charge recombination reactions Highly excited electronic states Non-adiabatic interactions (at small and large internuclear distances) Electronic resonant states electron scattering calculations Coulomb potential (long-range) Inclusion of angular momentum Diabatization of electronic states

5 Motivation

6 Motivation

7 Motivation Experiments are shutting down. Need for theory!

8 Mutual neutralization Quantum chemistry calculations (FCI or MRCI) Adiabatic potential energy curves, non-adiabatic interactions Electron scattering calculations Potentials of resonant states, autoionization widths Strict diabatization procedure Diabatic potentials, electronic couplings Solve time-independent Schrödinger equation for the nuclear motion Scattering matrix Compute differential and total cross section

9 Mutual neutralization Partial wave scattering matrix: Scattering amplitude: Differential cross section: + θ - Total cross section:

10 Energy (H) H + + H - mutual neutralization H 2 1 Σ g H + +H - H +H(n=3) H +H(n=2) Internuclear distance (a 0 ) Stenrup et al., PRA (2009)

11 Cross section (cm 2 ) H + + H - mutual neutralization Total MN cross section Present result Fussen and Kubach, 1986 Moseley et al., 1970 Peart and Hayton, E (ev) Stenrup et al., PRA (2009)

12 H + + H - mutual neutralization Total MN cross section Isotope dependence S. M. Nkambule, N. Elander, Å. Larson, X. Urbain and J. Lecointre PRA, 93, (2016).

13 H + + H - mutual neutralization Final state distributions Isotope dependence S. M. Nkambule, N. Elander, Å. Larson, X. Urbain and J. Lecointre PRA, 93, (2016).

14 H + + H - mutual neutralization Differential cross section S. M. Nkambule, N. Elander, Å. Larson, X. Urbain and J. Lecointre PRA, 93, (2016).

15 H + + H - mutual neutralization Differential cross section Isotope dependence S. M. Nkambule, N. Elander, Å. Larson, X. Urbain and J. Lecointre PRA, 93, (2016).

16 H + + H - mutual neutralization H 2 : Differential cross section Electronic inversion symmetry g/u states S. M. Nkambule, N. Elander, Å. Larson, X. Urbain and J. Lecointre PRA, 93, (2016).

17 H + + H - mutual neutralization H 2 : Differential cross section Electronic inversion symmetry g/u states Direct amplitude: Exchange amplitude: S. M. Nkambule, N. Elander, Å. Larson, X. Urbain and J. Lecointre PRA, 93, (2016).

18 Energy (H) He + + H - mutual neutralization -2.4 HeH 2 Σ H+He + H - +He + H+He * H + +He Electronic resonant states Internuclear distance (a 0 ) Electron scattering calculations combined with quantum chemistry

19 Cross section (cm 2 ) He + + H - mutual neutralization Total cross section Olamba 1996 Peart 1994 Gaily 1970 Chibisov 1997 Ermolaev 1992 Present calculation 4 He + +H Energy (ev)

20 Cross section (cm 2 ) He + + H - mutual neutralization Total cross section Isotope dependence He + + H He + + D - 3 He + + H - 3 He + + D Collision energy (ev)

21 Branching ratios He + + H - mutual neutralization Final state distributions 4 He + + D He(1s3p 1 P)+H He(1s3d 1 D, 3 D)+H He(1s3p 3 P)+H He(1s3s 1 S)+H He(1s3s 3 S)+H X. Urbain (unpublished) Collision energy (ev)

22 Branching ratios He + + H - mutual neutralization Final state distributions 4 He + + H He(1s2s 3 S)+H He(1s2s 1 S)+H He(1s2p 3 P)+H He(1s2p 1 P)+H He(1s3s 3 S)+H He(1s3s 1 S)+H He(1s3p 3 P)+H He(1s3p 1 P)+H He(1s3d 3 D)+H He(1s3d 1 D)+H Collision energy (ev)

23 He + + H - mutual neutralization HeH: Differential cross section

24 He + + H - mutual neutralization 4 He + + H - : Inclusion of autoionization

25 He + + H - mutual neutralization Inclusion of rotational couplings Pure precession approximation 1 2μR 2 Φ Σ J + L Φ Π 2l l + 1 2μR 2 0

26 Energy (H) HeH + electron recombination HeH + dissociative recombination Low energy electron capture to Rydberg states - MQDT High energy through the resonant states HeH + + e - HeH ** He* + H He + + H Å. Larson and A. E. Orel, PRA 59, 3601 (1999) Internuclear distance (a 0 )

27 HeH + electron recombination HeH + low energy DR simplified model Upper limit of the DR cross section Assumes predissociation is much faster than autoionization Works surprisingly well for many polyatomic systems

28 HeH + electron recombination e - + H 3 + e - + N 2 H + Ch. Jungen and S. T. Pratt PRL, 102, (2009) S. Fonseca dos Santos, A. E. Orel and Å. Larson unpublished

29 HeH + electron recombination HeH + low energy DR simplified model For the diatomic system autoionization cannot be neglected!

30 Conclusion Mutual neutralization: Quantum ab initio studies Highly excited states non-adiabatic interactions at large distances What method is most suitible for computing these couplings? Finite number of interacting states. Rotational couplings can we calculate them ab initio? Collisions between atomic and molecular ion? H H -

31 Conclusion Dissociative recombination: Good enough calculations: quantum chemisry - electron scattering Diabatization procedure: strict diabatization quasi-diabatization Final state distributions MQDT - wave packet Polyatomic systems: multi-fragmentation