Validity of energy gap representations of rotationally inelastic cross sections between polar molecules

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Abstract
In a collaborative investigation of rotational energy transfer between polar molecules, we have reported experimental state‐resolved cross sections for LiH( j=1)–HCl, DCl, HCN collisions [J. Chem. Phys. 71, 1670 (1979); 72, 6513 (1980)] and fully quantum cross sections for HF–HF collisions [J. Chem. Phys. 66, 1334 (1977) and to be published]. In the present article we apply both the exponential gap (EG) and power law (PL) parameterizations to the results of our experimental and theoretical study. Neither of these parameterizations is able to fit with high accuracy the HF–HF cross sections. Furthermore, this comparison reveals an inaccuracy in the statistical ’’prior’’ distribution which cannot be corrected by any multiplicative factor dependent on the energy gap. The fits were not greatly improved by the use of an alternative tensorial prior, suggested by group theoretic rather than statistical considerations. For the LiH scattering systems, the experimental cross sections can be fit extremely well by a power law dependence on the energy gap of the resolved LiH molecule. Unfortunately, it is improbable that either the PL or the EG fits to these partially averaged cross sections could be used to predict with any degree of accuracy the more fundamental fully resolved cross sections, as revealed by comparison with recently computed adiabatically corrected sudden cross sections [J. Chem. Phys. 71, 1683 (1979)].