Vibrational spectra and normal coordinate analysis of silyl pseudohalides. Part 3.—Silyl isocyanate

Abstract

We have studied the infrared spectra of several isotopic forms of silyl isocyanate matrix-isolated in nitrogen at 5–10 K, and of the normal form in Ar, CO₂ and allene matrices. The spectra show that the molecular skeleton is bent in all cases, in contrast with the linear skeletons found for heavier congeners. Normal coordinate analysis using the average frequencies for split fundamentals gives a reasonable force field which reproduces some molecular properties, but not the centrifugal distortion constants, which have large anharmonic contributions. A very restricted force field which reproduces vibration frequencies and isotope shifts for all three molecules SiH₃NCY (Y = O, S, Se) satisfactorily with only one diagonal and one off-diagonal force constant in the A₁ symmetry species varying with Y is proposed.