Binding energies of Ti+(H2)1–6 clusters: Theory and experiment

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Abstract
Formation of Ti + (H 2 ) n clusters (n=1–6) has been studied by both temperature-dependent equilibrium measurements and density functional theory(DFT). The successive binding energies (BDEs) were measured to be 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 addition of the first ligand. The first BDE is 10 kcal/mol when measured with respect to the excited state asymptote. This series of almost constant BDEs is unlike any other M + (H 2 ) n series. The present DFT calculations show these relatively constant BDE values for the Ti + (H 2 ) n clusters 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 here 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 first 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.