COLLISION-INDUCED DISSOCIATION MEASUREMENTS ON LI-6 - THE FIRST DIRECT MEASUREMENT OF THE LI+-OH2 BOND-ENERGY((H2O)(N), N=1)

Collision-induced dissociation of Li+(H2O)(n,) n = 1-6, with xenon (an d with argon for n = 1) is studied as a function of kinetic energy usi ng guided ion beam mass spectrometry. In all cases, the primary and lo west energy dissociation channel observed is endothermic loss of one w ater molecule. The cross section thresholds are interpreted to yield 0 and 298 K bond energies after accounting for the effects of multiple ion-molecule collisions, internal energy of the complexes, and dissoci ation lifetimes. The experimental bond energies determined here are in good agreement with previous experimental (high-pressure mass spectro metric, HPMS, measurements) and theoretical results for all complexes. In the case of Li+(H2O), the value determined here is actually the fi rst direct measurement of the bond energy. This value lies somewhat be low the value reported in the HPMS study which was extrapolated from d ata for larger clusters. Because the HPMS value has been used extensiv ely to establish an absolute Li+ affinity scale, this discrepancy is d iscussed in some detail.