MOLECULAR AND ELECTRONIC-STRUCTURE OF ZINC CARBYNE, HZNCH, AND ZINC STANNYNE, HZNSNH, FROM AB-INITIO CALCULATIONS

The electronic and molecular structures of both the ground state and s ome excited states of zinc carbyne and zinc stannyne have been investi gated using ab initio Hartree-Fock second order Moller-Plesset (MP2) a nd complete active space self-consistent-field (CASSCF) calculations. The ground state of HZnCH is the triplet (3) Sigma(-) in agreement wit h experiment and previous theoretical work, while the first excited st ate, the (1) Delta state, shows a classical distortion of the Renner-T eller type. The bond mechanism in these compounds has been carefully a nalyzed, and particularly the possibility of the presence of a Zn-C do uble bond is discussed. In contrast with zinc carbyne, the ground stat e of zinc stannyne is a singlet (1)A' while the first excited state is a triplet (3)A ''. These states can be viewed as arising from nonclas sical distortions featured by the corresponding (3) Sigma(-) and (1) D elta states due to strong electronic coupling. This loss of linearity has been related to the split between s-p tin levels and with the mode ls proposed for nonclassical distortions at multiple bonds.