New Magic Numbers in TixCy⁻ Anion Clusters and Implications for the Growth Mechanisms of Titanium Carbide Clusters

We report observation of new prominent peaks in the Ti x C y - anion mass spectra from laser vaporization experiments involving a pure Ti target with a CH 4 -seeded He carrier gas. Both photoelectron spectroscopy and density functional calculations were performed to obtain structural and bonding information for the new prominent anion clusters, including Ti 3 C 8 -, Ti 4 C 8 -, Ti 6 C 13 -, Ti 7 C 13 -, Ti 9 C 15 -, and Ti 13 C 22 - . For each cluster, we optimized several structures, evaluated their electron affinities (EAs), and simulated their single particle density of states (DOS). The calculated EAs and DOS of the different structures were then compared with the experimental photoelectron data. Good agreement between the experiments and calculations was found for the lowest energy isomers considered in each case. We found that three factors, i.e., the C 2 dimer, cubic framework, and layered structures, play essential roles in determining the structures and chemical bonding of the titanium carbide clusters. A growth pathway from Ti 3 C 8 to Ti 13 C 22 with Ti 6 C 13, Ti 7 C 13, and Ti 9 C 15 as intermediates is proposed and discussed.