Electronic structures, chemical bonds, and stabilities of Ta4Cn-/0 (n=0-4) clusters: Anion photoelectron spectroscopy and theoretical calculations

The electronic structures, chemical bonds and stabilities of Ta4Cn-/0 (n = 0-4) clusters are investigated by combining anion photoelectron spectroscopy with theoretical calculations. The vertical detachment energy values of Ta4Cn- (n = 0-4) anions are measured to be (1.16 +/- 0.08), (1.35 +/- 0.08), (1.51 +/- 0.08), (1.30 +/- 0.08), and (1.86 +/- 0.08) eV, and the electron affinities of neutral Ta4Cn (n = 0-4) are estimated to be (1.10 +/- 0.08), (1.31 +/- 0.08), (1.44 +/- 0.08), (1.21 +/- 0.08), and (1.80 +/- 0.08) eV, respectively. It is found that the geometry structure of Ta-4(-) cluster is a tetrahedron, and the most stable structure of Ta4C1- has a carbon atom capping one face of the Ta-4(-) tetrahedron, while in the ground state structure of Ta4C2- cluster, two carbon atoms cap two faces of the Ta-4(-) tetrahedron, respectively. The lowest-lying isomer of Ta4C3- cluster holds a cube-cutting-angle structure. The ground state structure of Ta4C4- is a 2 x 2 x 2 cube. The neutral Ta4Cn (n = 0-4) clusters have similar structures to their anionic counterparts and the neutral Ta4C4 cluster can be considered as the smallest cell for alpha-TaC face-centered cube crystal. The analyses of molecular orbitals reveal that the SOMO of Ta4C3- is mainly localized on one tantalum atom, inducing a low VDE. Our results show that the Ta-Ta metal bonds are replaced by Ta-C covalent bonds gradually as the number of carbon atoms increases in Ta4Cn-/0 (n = 0-4) clusters. The per-atom binding energy values of Ta4Cn-/0 (n = 0-4) clusters are higher than those of Ta-4+n(-/0) (n = 0-4) clusters, indicating that the formation of Ta-C covalent bonds may raise the melting point. The per-atom binding energy of neutral Ta4C4 is about 7.13 eV, which is quite high, which may contribute to the high melting point of alpha-TaC as an ultra-high temperature ceramic material.

Automated summary

The electronic structures, chemical bonds and stabilities of Ta4Cn-/0 (n = 0-4) clusters were investigated, revealing differences in energy parameters between anionic and neutral states, with Ta-C covalent bonds potentially raising the melting point.