Vibrational spectra and force constants of symmetric tops: High resolution spectra of monoisotopic H 3SiCl in the 2200-cm −1 region and rovibrational analysis of the ν1 and ν4 fundamentals

Abstract

The gas phase infrared spectra of monoisotopic H 3Si 35Cl and H 3Si 37Cl have been studied in the ν 1 ν 4 region near 2200 cm −1 with a resolution of 0.012 and 0.04 cm −1, respectively, and rotational fine structure for Δ J = ±1 branches has been resolved. In addition, some information on ν 3 + ν 4 of H 3Si 35Cl near 2750 cm −1 has been obtained. ν 1 and ν 4 are weakly coupled by Coriolis x, y resonance, B Ω 14ζ 14 ∼ 2 × 10 −3 cm −1 , only the upper states K′ = 2, l = 0 and K′ = 1, l = −1 being substantially affected. Local perturbation due to rotational l(±1, ±1)-type resonance with ν 3 + ν 5 +1 + ν 6 +1 and ν 3 + ν 5 +1 + ν 6 −1 is revealed in the Δ K = +1 and −1 branches, respectively. From a fit of the experimental line positions, standard deviations of 1.4 and 3.8 × 10 −3 cm −1, respectively, to a model with five interacting levels conventional excited state parameters and interaction constants have been obtained. In H 3Si 35Cl H 3Si 37Cl the fundamentals are ν 1, 2201.94380(15) 2201.9345(7) and ν 4, 2209.63862(8) 2209.6254(2) cm −1 , respectively. Q branches of the “hot” band ( ν 3 + ν 4) − ν 3 and of ν 4 of the 29Si and 30Si species have been detected.