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

Abstract The FTIR spectrum of H 3 SiD 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 ) (ν 0 = 4308.5667 cm −1 ) and (200, A 1 ) (ν 0 = 4307.8441 cm −1 ), were analyzed, and at higher wavenumbers, two weaker bands, namely (110, E ) at 4378.1950 cm −1 and (110, A 1 ) at 4375.9763 cm −1 , were analyzed. A total number of ∼1900 lines in the strong dyad and 1000 lines in the weak one were assigned and fitted with standard deviations of the residuals ≈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, A 1 ), (110, E ), and (110, A 1 ), respectively.