Reactions of Zn(4s4p 3P1) and Cd(5s5p 3P1) with SiH4

The first nsnp ³P₁ excited states of Cd and Zn atoms are shown to readily activate Si-H bonds in SiH₄. The nascent quantum state distributions of the CdH(v;N) and ZnH(v;N) products in the reactions of Cd(³P₁) and Zn(³P₁) with SiH₄ have been determined using the laser pump-probe technique. The results are discussed within the context of our current knowledge about the chemical interactions of valence M(nsnp ³P) excited states with Si-H, H-H, and C-H bonds, where M=Mg, Zn, Cd, and Hg. It is proposed that the high reactivity of M(nsnp ³P₁) states with H-H and Si-H bonds compared to C-H bonds is simply due to the lack of steric hindrance in the localized, side-on, M(npπ)-XH(σ*) donor-acceptor molecular orbital interactions, since the Si-H bond-length in SiH₄ is ∼1.5 Å compared to C-H bond lengths of ∼1.1 Å.