COLLISIONALLY COOLED SPECTROSCOPY: EXPERIMENTAL RESULTS AND APPROACHES TO A PARAMETERIZED THEORY

$^{1}$ S. Green. J. Chem. Phys. 82.4548 (1985). $^{2}$A. Palma and S. Green, J. Chem. Phys. 85, 1333 (1986).Author Institution: Department of Physics, Allegheny College; Department of Physics, Duke UniversityBy use of the collisional cooling technique, we have studied the helium pressure broadening of a number of species including $CO, CH_{3}F, H_{2}S, NO, DCI, OCS$, and HDO in the temperature region below 5 K. The size and variation with temperature of the cross sections can be qualitatively understood in terms of the rotational energy level density of the species and the depth of the shallow attractive well in the intermolecular potential. More quantitatively, Green$^{1}$ and Palma and Green$^{2}$ have shown for CO that `exact' close coupled calculations based on numerical potentials obtained by ab initio techniques can provide a good description of the experimental results. However, these numerical surfaccs do not appear to be an appropriate starting point for a parameterized descripron of experimental results because the number of constants required to describe the surfaces is very large. Furthermore, most of these parameters are not closely related to basic molecular properties. Experimental results will be shown and compared with the calculations. The issue of appropriate parameterization of the intermolecular potential for the fitting and prediction of observables will also be considered