Linewidths in OCS: Isotope effects, vibrational effects, temperature dependence, and T1/T2

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Abstract
A computer‐controlled microwave spectrometer has been used to record the frequency dependence of the absorption of the J=2←1 transition of OCS under varying conditions of pressure, temperature, and microwave power. From least‐squares fits of the data to Lorentzian line shapes, a variety of linewidths and linewidth parameters have been deduced. The linewidth parameter for the J=2←1 transition of 16O12C32S in the ground vibrational state has been determined to be 6.03±0.05 MHz/torr. The ratios of linewidth parameters for this transition for several other species to that for the ground state of 16O12C32S are: 16O12C34S, ground state, 0.987±0.003; 16O13C32S, ground state, 0.991±0.005; 18O12C32S, ground state, 0.966±0.018; 16O12C32S, v3=1, 1.024±0.026; 16O12C32S, v2l=2°, 0.978±0.003. The linewidth parameter for the ground state of the parent species was determined to be inversely proportional to the absolute temperature in the range 297–346 K. From comparison of theoretical and experimental power‐broadened lineshapes it is shown that T1/T2=1.04±0.10 for the transition.