DIPOLE MOMENT FUNCTION OF OCS

By means of infrared laser-microwave double resonance (LMDR) spectroscopy with intense electric field, we recently measured the precise dipole moments of OCS in the eleven vibrational states, $00^{0}0, 10^{0}0, 20^{0}0, 01^{1}0, 02^{0}0, 02^{2}0, 03^{1}0, 04^{0}0, 12^{0}0, 14^{2}0$, and $22^{O}O$, of the normal species, and in the two vibrational states, $00^{0}0$ and $02^{0}0$. of both $OC^{34}S$ and $O^{13}CS$. These dipole moments, which are accurate to $2 \\times 10^{-5} D$, were combined with the previous MBER results for $00^{0}0$ and $01^{1}0$ states of the normal, $OC^{34}S, O^{13}CS$, and $^{18}OCS$ $species^{1}$ and the transition moments for various vibrational bands obtained from infrared intensity $measurements^{2}$, to determine the dipole moment function of OCS. Curvi-linear coordinates were used to describe the vibrational displacements. The dipole moment was represented in terms of the components parallel and perpendicular to the C-O (or C-S) bond. The dipole moments of various isotopic species may thus be analyzed simultaneously. The vibrational wave functions were calculated by direct diagonalization method with the force field given by Foord $et al.^{3}$ Signs of some transition moments were inferred in the course of the analysis from the vibrational and isotopic variations of the dipole moment. The dipole moment function thus determined resulted in a satisfactory agreement between the observed and calculated moments. The vibrational changes of dipole moment and the slight isotope dependences were adequately accounted for. (1) J.M.L.J. Reinartz and A. Dymanus, Chem. Phys. Lett. 24, 346-351 (1974). (2) R.T. Kagann. J. Mol. Spectrosc. 94, 192-198 (1982). (3) A. Foord. J.G. Smith, and D.H. Whiffen, Mol. Phys. 29, 1685-1704 (1975).