High-Resolution Study of the First Stretching Overtones of H3Si79Br☆

Abstract The Fourier transform infrared spectrum of monoisotopic H 3 Si 79 Br (resolution 7.7 × 10 −3 cm −1 ) was studied from 4200 to 4520 cm −1 , in the region of the first overtones of the Si–H stretching vibration. The investigation of the spectrum revealed the presence of two band systems, the first consisting of one parallel (ν 0 = 4340.2002 cm −1 ) and one perpendicular (ν 0 = 4342.1432 cm −1 ) strong component, and the second of one parallel (ν 0 = 4405.789 cm −1 ) and one perpendicular (ν 0 = 4416.233 cm −1 ) weak component. The rovibrational analysis shows strong local perturbations for both strong and weak systems. Seven hundred eighty-one nonzero-weighted transitions belonging to the strong system [the (200) manifold in the local mode picture] were fitted to a simple model involving a perpendicular component interacting by a weak Coriolis resonance with a parallel component. The most severely perturbed transitions (whose ‖obs–calc‖ values exceeded 3 × 10 −3 cm −1 ) were given zero weights. The standard deviations of the fit were 1.0 × 10 −3 and 0.69 × 10 −3 cm −1 for the parallel and the perpendicular components, respectively. The weak band system, severely perturbed by many “dark” perturbers, was fitted to a model involving one parallel and one perpendicular band, connected by a Coriolis-type resonance. The K" · ΔK = +10 to +18 subbands of the perpendicular component, which showed very high observed − calculated values (∼0.5 cm −1 ), were excluded from this calculation. The standard deviations of the fit were 11 × 10 −3 and 13 × 10 −3 cm −1 for the parallel and the perpendicular components, respectively.