Variation of Line Width with Rotational State and Temperature in the Microwave Spectrum of OCS

Abstract

The earlier measurements on the self-broadening of OCS rotational transitions by Johnson and Slager have been extended. Measurements have been made at constant pressure on seven rotational transitions in the ground vibrational state from $J=3\mathrm{}\to 4$ to $J=15\mathrm{}\to 16$ and at dry ice and room temperatures. The data have been interpreted by a simple theory which assumes a constant contribution to line width from dipole-dipole interactions and an additional $J$-dependent contribution from rotational resonance interactions. Empirically determined temperature dependence is introduced for each contribution. This interpretation, when fit to the observed line widths, $\Delta \nu$ results in the expression $\Delta \nu =\frac{1815}{T}+0.00321\mathrm{}{T}^{\frac{1}{2}}{\mathrm{}(J+1\mathrm{})\mathrm{}}^2{e}^{-\frac{\mathrm{hBJ}(J+1\mathrm{})\mathrm{}}{\mathrm{kT}}} \mathrm{Mc}/sec$ at 1-mm Hg pressure. The collision diameters for OCS are found to be approximately linear functions of the rotational state and independent of temperature.