High resolution infrared study of SbHD2: The ground state and the Sb–H stretching bands ν1 and 2ν1

Abstract High resolution infrared spectra of 121 SbHD 2 and 123 SbHD 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 123 SbHD 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 123 SbHD 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 121 SbHD 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 121 SbHD 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 123 SbHD 2 , 121 SbHD 2 , 123 SbH 2 D, and 121 SbH 2 D. Relations between the harmonic frequencies and between the anharmonicity constants obtained in the expanded local mode theory, for the XH 3  → XH 2 D/XHD 2 isotopic substitution, have been compared with those obtained in the present study.