Dipole moment function of carbonyl sulfide from analysis of precise dipole moments and infrared intensities

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Abstract
Precise (±3×10−5 D) dipole moments of OCS in 11 vibrational states (0000, 1000, 2000, 0110, 0200, 0220, 0310, 0400, 1200, 1420, 2200) of the normal species and two states (0000 and 0200) of both OC34S and O13CS derived from our recent LMDR (infrared laser–microwave double resonance with intense electric field) measurements were combined with the previous MBER (molecular beam electric resonance) results for the 0000 and 0110 states of the normal, 34S, 13C, and 18O species and the transition moments for various vibrational bands obtained from infrared intensity measurements, to determine the dipole moment function. Curvilinear coordinates were used to describe the vibrational displacements. The dipole moment vector was represented in terms of the components parallel and perpendicular to the C–O bond. Thus the dipole moments of various isotopic species may be analyzed simultaneously. The dipole moments and the transition moments were calculated as the diagonal and nondiagonal matrix elements of dipole moment operator between the vibrational wave functions which were obtained by direct diagonalization method using an accurate anharmonic force field. The signs of the transition moments were inferred from the vibrational and isotopic dependence of dipole moment in the course of the analysis. The dipole moment function thus determined well reproduced the observed values of the average dipole moments and the transition moments. The vibrational changes and the slight isotopic dependence of the dipole moment were adequately accounted for.