EXCITATION OF SYMMETRICAL AND ASYMMETRIC STRETCH IN A SYMMETRICAL TRIATOMIC MOLECULE - A TIME-DEPENDENT (COLLINEAR) ANALYSIS OF THE IHI-PHOTODETACHMENT SPECTRUM

We present time-dependent quantum calculations for the collinear IHI- --> IHI transition, which has been studied before by time-independent methods by Schatz [J. Chem. Phys. 90, 4847 (1990)] and Bowman and Gazdy [J. Phys. Chem. 93, 5129 (1989)]. The mass ratio of the atoms involved determines the time scales of the symmetric stretch on the one hand and the asymmetric stretch on the other. Both modes are excited in the transition complex. We demonstrate how resonances in the spectrum can be related to the motion of the ionic wave function on a potential energy surface for IHI. The dynamical picture is complementary to the one which is obtained from the stationary state calculations. The system under consideration differs in many aspects from other examples of symmetric triatomic molecules. The dynamics corresponding to structures in the spectrum reveals the peculiarities of heavy-light-heavy systems.