IR Transition Moment Directions in Matrix-Isolated Dimethylsilylene and 1-Methylsilene

摘要

Irradiation of martrix-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 converts 2 back into 1 allowed a determination of the absolute values of polarization angles of seven in-plan polarized IR transitions of 2 relative to the pi pi* transition moment. The resulting map of the IR transition moment directions in the molecule of 1 provides strong support for the detailed assignment of the nature of the vibrational motions involved. Along with other data, the results leave very little doubt as to the correctness of the structural and vibrational assignments in 1 and 2.