Low-lying quasibound rovibrational states of H2 16O**

Abstract

A complex coordinate scaling (CCS) method is described allowing the quantum chemical computation of quasibound (also called resonance or metastable) rovibrational states of strongly bound triatomic molecules. The molecule chosen to test the method is H2 16O, for which an accurate global potential energy surface, a previous computation of a few resonance states via the complex absorbing potential (CAP) method, and some Feshbach (J = 0, where J is the quantum number characterising overall rotations of the molecule) and shape (J ≠ 0) resonances measured via a state-selective, triple-resonance technique are all available. Characterisation of the computed resonance states is performed via probability density plots based on CCS rovibrational wavefunctions. Such plots provide useful details about the physical nature of the resonance states. Based on the computations and the resonance plots, the following useful facts about the resonance states investigated are obtained: (a) Feshbach resonances are formed by accumulation of a large amount of energy in either the non-dissociative bending or symmetric streching modes, excitations by more than five quanta are not uncommon; (b) there are several resonance states with low and medium bending excitation, the latter are different from the states observed somewhat below dissociation by the same triple-resonance technique; (c) several types of dissociation bahavior can be identified, varying greatly among the states; (d) several pairs of J = 0 and J = 1 Feshbach resonance states can be identified which differ by rigid-rotor type energies; and (e) the lifetimes of the assigned J = 1 rovibrational Feshbach resonances are considerably longer than the lifetimes of their J = 0 vibrational counterparts.