Abstract: Irradiation of matrix-isolated dimethyldiazidosilane yields dimethylsilylene (1) as the major product. Photoselection on the 450-nm absorption band of 1 with polarized 488- nm light, which converts 1 into 1-methylsilene (2), permitted the assignment of six IR transitions of 1 and twelve IR transitions of 2 as in-plane or out-of-plane polarized. Photoselection on the 260-nm absorption band of 2 with polarized 248-nm light, which ...