COLLISIONAL ALIGNMENT OF MOLECULAR ROTATION - SIMPLE-MODELS AND TRAJECTORY ANALYSIS

We report simple model treatments and quasiclassical trajectory calcul ations dealing with collisional relaxation and alignment of molecular rotation in atom-diatom collisions. Since these models and trajectorie s involve single collisions, our results do not pertain directly to al ignment due to supersonic expansions but nonetheless serve to elucidat e some major aspects that need to be taken into account for mechanisti c interpretations. By comparing alignments found for different potenti al functions (pairwise additive Lennard-Jones, purely repulsive invers e power, and hard ellipsoid) over a wide range of collision energies a nd impact parameters, we map out three qualitatively distinct regimes. These include ''near-Gorter'' and ''anti-Gorter'' regimes, dominant f or direct collisions at small and large impact parameters, respectivel y, and ''pseudo-Gorter'' behavior found typically for low energy, larg e impact parameter collisions subject to soft, sticky potentials.