Density Functional Investigation of Various States of the Molecules TcC, TcC₂, ScC₂, and YC₂

Abstract

Spin-polarized density functional theory has been used to investigate the C2v, C∞v and D∞h isomers of the molecules MC2, M = Sc, Y, Tc, and selected states of the diatomic molecule TcC. According to the theory, the ground state of the diatomic is the 4Σ+ TcC isomer. Bond length comparisons between the doublet and quartet isomers reveal the ground state has a double bond, and the first excited state (2Δ TcC) is triple bonded. For MC2, M = Sc, Y, Tc, numerous minima were located, including spin states of the same symmetry. Cyclic isomers were identified as the ground states for each of the three metals. The minimized C−C bond length for X̃ 2A1 TcC2 is 1.58 Å, and is close to typical values for carbon−carbon single bonds, whereas the corresponding bond distances in X̃ 2A1 MC2, M = Sc, Y, are closer to typical values for carbon−carbon double bonds. Examination of the isomer structures and energies for TcC2 suggests a preference for double bond formation with the carbon atoms of the C2 unit. This is in contrast to scandium and yttrium dicarbides which prefer to form single bonds with the C2 unit.