HG-SENSITIZED PHOTOLYSIS OF ME(3)SIH .1. A QUANTITATIVE APPROACH TO THE MECHANISM

The mercury-sensitized photolysis of Me(3)SiH was studied as a functio n of the exposure time, substrate pressure and light intensity, and in the presence of the additives MeOH and H-2. Two primary processes wer e observed: hydrogen abstraction from the Si-H bond and, to a minor ex tent, from the C-H bond. The sum of the quantum yields of the two prim ary processes is only 0.8. The main part of the reaction mechanism, wh ich concerns the reactions of the Me,Si radical, can be quantitatively explained by a previous investigation of the direct photolysis of Me, Si (Ahmed et al., J. Phorochem. Photobiol. A: Chern., 86 (1995) 33). W ith the rate constants given by Ahmed et al., the experimental values can be satisfactorily reproduced by computer simulations. In particula r, it is confirmed that silaethylene reacts in an almost collision-con trolled manner with radicals and the disproportionation reactions of S i-centred radicals leading to an Si=C double bond play only a minor ro le. The ratio of disproportionation to combination of the Me,Si radica l was determined to be 0.07 +/- 0.01.