XVIth International Workshop on
Quantum Systems in
Chemistry and Physics
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Non-adiabatic effects in the action of radiation on molecular systems
Marie-Christine Bacchus-Montabonel
Laboratoire de Spectrométrie Ionique et Moléculaire, CNRS et Université Lyon I, 43 Bd. Du 11 Novembre 1918, 69622 Villeurbanne Cedex, France, bacchus@lasim.univ-lyon1.fr
Non-adiabatic interactions are the driving step in a number of mechanisms and special attention should be paid to the critical regions of the potential energy surfaces as avoided crossings or conical intersections where mixing and reorganization of electronic configurations may occur. These interactions may be observed in a large number of processes as phodissociation or charge transfer reactions. We have developed non-adiabatic methods based on wave packet propagation to calculate cross sections and rate constants in ion-atom charge transfer collisions [1]. This approach may be particularly interesting for polyatomic systems of increasing complexity since it allows the possibility of separating the total configuration space into a subspace of n internal active coordinates which are quantum mechanically treated on ab initio potential energy surfaces, while inactive coordinates are treated in an approximate way, as in the constrained Hamiltonian methodology [2]. Such an approach has been applied on the very interesting example of the competitive dissociation of C-Cl and C-Br bonds in bromoacetyl chloride Br-CH2-COCl photodissociation [3]. In such a process, non-adiabatic effects induce a trapping of the system before dissociation leading thus preferentially to C-Cl breaking, although the C-Br bond should be weaker with regard to the relative height of energetic barriers along the reaction path.

In a different domain, action of ionizing radiations with biological tissues is known to induce severe damage to DNA. However, it has been shown [4] that important damage is not due to the radiation itself, but to secondary particles generated along the track after interaction of the radiation with the medium. We have studied the action of secondary ions with biomolecules; they may be involved either in direct process with biomolecules, or in indirect ones involving interaction of ions with the medium. The radiosensitivity of halouracils is analyzed in the direct collision with C4+ ions [5]. We present examples of indirect processes with the C2+ + OH and C2+ + CO collision systems which are driven by non-adiabatic interaction around avoided crossings between the different entry and exit channels [6].

References

1.N. Vaeck, M.C. Bacchus-Montabonel, E. Baloďtcha, M. Desouter-Lecomte, Phys. Rev. A 63, 042704 (2001).
2.D. Lauvergnat and A. Nauts, J. Chem. Phys. 116, 8560 (2002).
3.B. Lasorne, M.C. Bacchus-Montabonel, N. Vaeck, M. Desouter-Lecomte, J. Chem. Phys. 120, 1271 (2004).
4.B.D. Michael, P.D. O'Neill, Science 287, 1603 (2000).
5.M.C. Bacchus-Montabonel and Y.S. Tergiman, Chem. Phys. Lett (2011) (in press)
6.E. Rozsályi, E. Bene, G.J. Halász, Á. Vibók, M.C. Bacchus-Montabonel, Phys. Rev. A 81, 062711 (2010).


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