Decay dynamics of triatomic molecules: Quantum calculations for non-symmetric linear systems

Abstract

Abstract The direct resonance search method of Basilevsky and Ryaboy, is applied to study quantum decay dynamics of a linear non-symmetric molecule ABC* → AB+C. The system is characterized by the ratio of the valence vibration frequencies ω1/ω3 = 5.3 and the dissociation energies D(AB–C) = 22.25 hω3 and D(A–BC) = 55.65 hω3 (values typical of HOX molecules with X a halogen atom). The hamiltonian is defined parametrically in natural reaction coordinates. The inherent feature of the model system is that the vibrationally non-adiabatic interaction is localized within a narrow region of the minimum energy path inside the potential well. It is shown that two decay regimes (weak and strong coupling) are possible depending on the location of the non-adiabaticity region on the reaction path. The weak-coupling regime is characterized by a hierarchy of widths of quasi-bound states: an isoenergetic state with more excited vibration ω1 possesses a considerably less width. In the strong-coupling regime the widths of all quasi-bound states are ranged within a narrow energy interval. The mean values of the widths averaged over the energy range of ≈ hω3 (the widths of “mixed” states) agree well with the predictions of the statistical theory. In a modified potential (D(A–BC) = 24.75 hω3) permitting the cleavage of either bond, A–B or B–C, partial decay widths are calculated at reasonable energies for several accessible channels A+BC(0) ← ABC* → AB(v)+C(v = 0.1). It is found that for some quasi-bound states the ratio of partial widths γBC/γAB > 10, and therefore they decay mainly into a channel with a higher energy.