Neutral tantalum-carbide clusters: A multiphoton ionization and density functional theory study

Neutral tantalum-carbide clusters, TamCn (m = 1-6, n = 1-7), have been form ed in a supersonic expansion following the reaction of tantalum and acetyle ne in a laser ablation source. These clusters have been subjected to multip hoton ionization at 532 and 355 nm and the mass spectra recorded in a refle ction lime-of-night mass spectrometer. The cluster distributions show a dro p off after m = 4 suggesting the stabilization of clusters containing four tantalum atoms. We have investigated the structures of these clusters using density functional theory and shown that the smaller clusters tend to Form fragments of face-centered cubes, culminating in the formation of a distor ted cube of stoichiometry Ta4C4. The structure of Tr4C4 is shown to be a di storted tetrahedron, or "butterfly", made up of four tantalum atoms with a carbon atom bonded to each face. The theoretical calculations also indicate that clusters containing three tantalum atoms form a triangle and that the re is competition for the carbon atoms to bond to either the face or the ed ge of the tantalum triangle.