High resolution infrared study of SbHD2: The ground state and the Sb-H stretching bands nu1 and 2nu1

none5High resolution infrared spectra of (SbHD2)-Sb-121 and (SbHD2)-Sb-123 have been studied in the region of nu(1), the Sb-H stretching fundamental, from 1780 to 1990 cm(-1). The 2 nu(1) stretching overtone band of (SbHD2)-Sb-123, located in the 3640-3790 cm(-1) range, has also been investigated. The SbHD2 molecule is an asymmetric rotor of C-s symmetry with the asymmetry parameter kappa = 0.61. The nu(1) band is of hybrid type, formed by strong C-type and weak B-type transitions, and almost unperturbed. For (SbHD2)-Sb-123, 2092 transitions have been assigned: 70% of these belong to the C component, the other 30% are of B-type. The assigned transitions have been fitted using a Watson type S-reduced Hamiltonian in the lilt representation, with a standard deviation of the fit sigma = 0.45 x 10(-3) cm(-1). In order to determine the ground state parameters all possible ground state combination differences (GSCD) have been generated from the v, transitions. In total, 3942 GSCD up to J '' = 27, K ''(a) = 25, and K ''(c) = 20 have been fitted with sigma = 0.52 x 10(-3) cm(-1). Only C-type transitions have been observed in the weak 2 nu(1) overtone band. The 556 assigned transitions have been fitted with sigma = 2.6 x 10(-3) cm(-1) using the same Hamiltonian as for nu(1). In the nu(1) band of (SbHD2)-Sb-121 771 C-type transitions have been assigned, and the nu(1) = 1 spectroscopic constants obtained from a fit with sigma = 0.70 x 10(-3) cm(-1). Using 618 GSCD the ground state spectroscopic constants of (SbHD2)-Sb-121 have been derived with a = 1.0 x 10(-3) cm(-1). The molecular parameters for the ground and the nu(1) = 1 states of the two isotopologues agree well. The quartic theoretical ab initio force field of SbH3 has been used to predict all relevant spectroscopic parameters for (SbHD2)-Sb-123, (SbHD2)-Sb-121, (SbHD2)-Sb-123, and (SbH2D)-Sb-121. Relations between the harmonic frequencies and between the anharmonicity constants obtained in the expanded local mode theory, for the XH3 -> XH2D/XHD2 isotopic substitution, have been compared with those obtained in the present study. (C) 2010 Elsevier Inc. All rights reserved.noneE. Canè; L. Fusina; R. Tarroni; M. Litz; H. BuergerE. Canè; L. Fusina; R. Tarroni; M. Litz; H. Buerge