Reactions of Zn(4 s 4 p  3 P 1) and Cd(5 s 5 p  3 P 1) 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.