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

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→4 to J=15→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, Δν results in the expression Δν=1815/T+0.00321T1/2(J+1)²e^-hBJ(J+1)/kT 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.