Exploring the transition state for the Li+HF→LiF+H reaction through the A←X absorption spectrum and X←A stimulated emission pumping

The A(2 (2)A') first excited electronic state of LiHF has been calculated (about 3300 points at MRDCI level) and an analytical fit of the global potential energy surface is presented. The A <--X absorption spectrum is simulated at 10 K between 9000 and 13 000 cm(-1), what involves the calculation of excited bound states for moderately high total angular momentum. These quasibound levels of the A state can only decay by electronic predissociation (EP) towards the X ground state, since the spontaneous radiative emission is considered to be very slow. The decay of such states has been estimated using a perturbative approach and it is found that LiF products are produced with a high efficiency (> 80%). The X <--A stimulated emission pumping spectra is simulated for several initial quasibound levels. These spectra allow the examination of the reaction dynamics specially near the transition state region, and the first photon excitation may act as a rotational filter, reducing the problem of the partial wave average involved in reactive collisions. The high reaction efficiency of this last process is also discussed. (C) 2001 American Institute of Physics.