Complexes of Li atoms with water and ammonia: a combined neutralization-reionization mass spectrometry and theoretical study

The hypervalent complexes of Li atom with water and ammonia, viz. Li-OH2 an d Li-NH3, are generated in the gas phase by neutralization of Li+-OH2 and L i+-NH3, respectively. The mass spectra obtained by subsequent reionization similar to0.3 mus later clearly indicate that the neutral complexes Li-OH2 and Li-NH3 are stable species in the gas phase, as had been predicted by th eory. Li-OH2/Li-NH3 dissociate partly to Li+H2O/NH3 within the timescale of the experiments, the dissociating fraction of the water complex being larg er. Parallel ab initio calculations reveal that the more extensive dissocia tion of Li-OH2 versus Li-NH3 is the result of a lower binding energy (51 ve rsus 62 kJ mol(-1) for Li-OH2 and Li-NH3, respectively) and a less favorabl e Franck-Condon factor for transitions between Li-OH2 and Li+-OH2, as compa red to transitions between Li-NH3 and Li+-NH3. (C) 2001 Elsevier Science B. V.