A three-dimensional time-dependent wavepacket calculation for bound and quasi-bound levels of the ground state of HCO: resonance energies, level widths and CO product state distributions

Abstract

A newly developed scheme for treating poiar angle coordinates has been used in the solution of the time-dependent Schrödinger equation for a triatomic system in Jacobi coordinates. This has been applied to calculations of the energies of bound vibrational levels and quasi-bound resonances of HCO in its ground electronic state. Initial wavepackets have been chosen to simulate the B ²A′–X ²A′ emission spectrum of HCO (the ‘hydrocarbon flame bands’), and to represent dissociation on the X²A′ surface following Renner–Teller-induced internal conversion from the òA″ state. A revised geometry r_CH= 1.12 Å, r_co= 1.37 Å and α_HCO= 107Å has been derived for the B;state by comparison of theoretical and experimental Franck–Condon factors. The out-going waves have been analysed to yield vibration–rotation population distributions at all energies for the CO dissociation product. The wavefunctions for selected quasi-bound vibrational levels have been generated by resonant driving of the time-dependent equation, and graphically illustrate the vibrational redistribution accompanying dissociation.

The pattern of lifetimes and product state distributions is in good qualitative agreement with the available experimental data, and is found to be correlated with empirical vibrational quantum numbers for the quasi-bound resonances. The dissociation dynamics are significantly different for states with high v₂ from those for high v₃. These variations are discussed in relation to the nature of the ab initio potential-energy surface and of the vibrational motion for each state.