Exploring the transition state for the Li+HF -> LiF+H reaction through theA <- 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 poten tial energy surface is presented. The A <--X absorption spectrum is simulat ed 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 qua sibound levels of the A state can only decay by electronic predissociation (EP) towards the X ground state, since the spontaneous radiative emission i s considered to be very slow. The decay of such states has been estimated u sing a perturbative approach and it is found that LiF products are produced with a high efficiency (> 80%). The X <--A stimulated emission pumping spe ctra is simulated for several initial quasibound levels. These spectra allo w the examination of the reaction dynamics specially near the transition st ate region, and the first photon excitation may act as a rotational filter, reducing the problem of the partial wave average involved in reactive coll isions. The high reaction efficiency of this last process is also discussed . (C) 2001 American Institute of Physics.