Ab initio studies of the reactions of M(S-1, P-3, and P-1) with SiH4 (M=Cd, Hg)

The reactions of Cd(S-1:5s(2), P-3,P-1:5s(1)5p(1)) and Hg(S-1:6s(2), P-3,P- 1:6s(1)6p(1)) with SiH4 have been studied through multiconfiguration self-c onsistent-field (MCSCF) (with relativistic effective core potentials) follo wed by extensive variational and perturbational second-order multireference Moller-Plesset configuration interaction by perturbation selected by itera tive process (CIPSI) calculations using extended Gaussian basis sets. It wa s found that both metal atoms in their P-3(ns(1)np(1)) state break the Si-H bond of silane spontaneously, leading directly to the MH + SiH3 final prod ucts, in agreement with the experimental results of this reaction for Cd. O ne important qualitative difference between the Cd and Hg(P-3) reactions is that for the former an unstable intermediate was found, whereas for the la tter no intermediate exists at all. Again, for both atoms, the P-1(ns(1)np( 1)) state is also inserted in the Si-H bond and the corresponding interacti on surface shows an avoided crossing with the lowest-lying X (1)A' potentia l surface, adiabatically correlated with the M(S-1:ns(2)) + SiH4 reactants. This interaction leads eventually to the MH + SiH3 products. The structure of these HMSiH3 intermediates, diabatically correlated with the M(P-1:ns(1 )np(1)) + SiH4 reactants, was carefully studied, as well as the dissociatio n channels leading to the MH + SiH3 and H + MSiH3 products. Accurate energy differences between all these species are also reported. The theoretical r esults obtained for the mercury reaction are discussed in light of the very recent experimental results of Legay-Sommaire and Legay [J. Phys. Chem. A 102, 8579 (1998)] for the insertion of Hg(P-3:4s(1)4p(1)) in SiH4 over N-2 and rare gas matrices. Our results confirm their conclusion that the photoc hemical insertion of Hg(P-3) into the Si-H bond of silane proceeds without any activation barrier. (C) 1999 American Institute of Physics. [S0021-9606 (99)30322-6].