THE FIRST SI-H STRETCHING OVERTONE OF H3SID - EMERGENCE OF LOCAL MODEEFFECTS

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) (nu(0) = 4308.5667 cm(-1)) and (200, A(1)) (nu(0) = 4307.8441 cm(-1)), were analyzed, and at higher wavenumbers, two we aker bands, namely (110, E) at 4378.1950 cm(-1) and (110, A(1)) at 437 5.9763 cm(-1), were analyzed. A total number of similar to 1900 lines in the strong dyad and 1000 lines in the weak one were assigned and fi tted with standard deviations of the residuals approximate to 0.0008 c m(-1). The strong system (200) is close to local mode behavior, with n o x, y Coriolis term needed and only a small z Coriolis term, and simp le arithmetic relations between vibration-rotation parameters are fulf illed 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)), resp ectively. (C) 1998 Academic Press.