BINDING-ENERGIES OF TI-2)(1-6) CLUSTERS - THEORY AND EXPERIMENT((H)

Formation of Ti+(H-2)(n) clusters (n = 1-6) has been studied by both t emperature-dependent equilibrium measurements and density functional t heory (DFT). The successive binding energies (BDEs) were measured to b e 7.5+/-0.5, 9.7+/-0.6, 9.3+/-0.7, 8.5+/-0.4, 8.2+/-0.4, and 8.7+/-0.4 kcal/mol for n = 1-6, respectively. The relatively low value of the n = 1 BDE is due to a curve crossing from the Ti+[a(4)F(sd(2))] ground state to the Ti+[b(4)F(d(3))] first excited asymptote with the additio n of the first ligand. The first BDE is 10 kcal/mol when measured with respect to the excited state asymptote. This series of almost constan t BDEs is unlike any other M+(H-2)(n) series. The present DFT calculat ions show these relatively constant BDE values for the Ti+(H-2)(n) clu sters are due to an electronic occupation which allows the Ti+ ion to interact equally with up to six H-2 ligands. Bond lengths, geometries, and vibrational frequencies from the DFT calculations are reported he n for all clusters. The influence of basis set size and computational method on the first two clusters was also examined. It was determined that a multireference wave function was required to describe these fir st two clusters accurately. A possible crossing to the lowest doublet potential energy surface was examined for Ti+(H-2)(4) and found to be endoergic. (C) 1997 American Institute of Physics.