Transition state spectroscopy of the excited electronic states of Li-HF

In this work the LiHF(A,B,B'<--X) electronic spectrum is simulated and compared with the experimental one obtained by Hudson [J. Chem. Phys. 113, 9897 (2000)]. High level ab initio calculations of three (2)A' and one (2)A" electronic states have been performed using a new atomic basis set and for a large number of nuclear configurations (about 6000). Four analytic global potential energy surfaces have been fitted. The spectrum involved very excited rovibrational states, close to the first dissociation limit, at high total angular momentum. Two different methods have been used, one based on bound state and the second one on wave packet calculations. Different alternatives have been used to simulate the relatively high temperatures involved. The agreement obtained with the experimental spectrum is very good allowing a very simple assignment of the peaks. They are due to bending progressions on the three excited electronic states. A simple model is used in which only rotational degrees of freedom are included, which simulates the spectrum in excellent agreement with the experimental one, providing a nice physical interpretation. Moreover, the remaining theoretical/experimental discrepancies have been attributed to nonadiabatic effects through the extension of this model to a diabatic representation of excited coupled electronic states. (C) 2003 American Institute of Physics.