The First Si-H Stretching Overtone of H3SiD: Emergence of Local Mode Effects

The FTIR spectrum of H3SiD in the 4100-4500-cm-1 region was recorded at Doppler-limited resolution, and four bands were studied. At lower wavenumbers, two strong bands, which in the local mode picture can be assigned to (200, E) (nu0 = 4308.5667 cm-1) and (200, A1) (nu0 = 4307.8441 cm-1), were analyzed, and at higher wavenumbers, two weaker bands, namely (110, E) at 4378.1950 cm-1 and (110, A1) at 4375.9763 cm-1, were analyzed. A total number of approximately 1900 lines in the strong dyad and 1000 lines in the weak one were assigned and fitted with standard deviations of the residuals approximately 0.0008 cm-1. The strong system (200) is close to local mode behavior, with no x, y Coriolis term needed and only a small z Coriolis term, and simple arithmetic relations between vibration-rotation parameters are fulfilled as expected. The local mode behavior of the weak system (110) is less pronounced, but z and x, y Coriolis effects are smaller than in the Si-H stretching fundamentals. Comparison of computed and observed spectra provided a good estimate for the ratios of transition moments of the different bands: they are, in absolute value, proportional to 3.5:1.75:1:1 for (200, E), (200, A1), (110, E), and (110, A1), respectively. Copyright 1998 Academic Press.