High resolution infrared study of SbHD 2: The ground state and the Sb–H stretching bands ν1 and 2 ν1

Abstract

High resolution infrared spectra of 121SbHD 2 and 123SbHD 2 have been studied in the region of ν 1 , the Sb–H stretching fundamental, from 1780 to 1990 cm −1. The 2 ν 1 stretching overtone band of 123SbHD 2, located in the 3640–3790 cm −1 range, has also been investigated. The SbHD 2 molecule is an asymmetric rotor of C s symmetry with the asymmetry parameter κ = 0.61. The ν 1 band is of hybrid type, formed by strong C-type and weak B-type transitions, and almost unperturbed. For 123SbHD 2, 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 III l representation, with a standard deviation of the fit σ = 0.45 × 10 −3 cm −1. In order to determine the ground state parameters all possible ground state combination differences (GSCD) have been generated from the ν 1 transitions. In total, 3942 GSCD up to J ″ = 27, K a ″ = 25, and K c ″ = 20 have been fitted with σ = 0.52 × 10 −3 cm −1. Only C-type transitions have been observed in the weak 2 ν 1 overtone band. The 556 assigned transitions have been fitted with σ = 2.6 × 10 −3 cm −1 using the same Hamiltonian as for ν 1 . In the ν 1 band of 121SbHD 2 771 C-type transitions have been assigned, and the v 1 = 1 spectroscopic constants obtained from a fit with σ = 0.70 × 10 −3 cm −1. Using 618 GSCD the ground state spectroscopic constants of 121SbHD 2 have been derived with σ = 1.0 × 10 −3 cm −1. The molecular parameters for the ground and the v 1 = 1 states of the two isotopologues agree well. The quartic theoretical ab initio force field of SbH 3 has been used to predict all relevant spectroscopic parameters for 123SbHD 2, 121SbHD 2, 123SbH 2D, and 121SbH 2D. Relations between the harmonic frequencies and between the anharmonicity constants obtained in the expanded local mode theory, for the XH 3 → XH 2D/XHD 2 isotopic substitution, have been compared with those obtained in the present study.