Correlation functions of the Pi--Σ and the Σ--Σ vibration--rotation bands of a triatomic linear molecule mixed with dense rare gases

The degenerate and nondegenerate rotation--vibration bands of OCS mixed with rare gases have been scanned in the density range 15--300 amagat. The related correlation functions have been corrected for the hot band perturbations and compared with usual rotational models. None of the models fit both correlation functions. A comparison with experimental correlation functions arising from other linear molecules mixed with rare gases shows that a convenient rotational relaxation model would have to consider explicitly the mean square torque at least in the range of density explored. Such a requirement is fulfilled by using a memory function proposed by Steele. The correlation functions are then very well predicted for both vibrations using the same values of the parameters. The adjusted mean square torque values are then successfully compared with those determined directly by a spectral moment measurement method