Adiabatic invariance treatment of hitting collisions between ions and symmetrical top dipolar molecules

The adiabatic invariance method of calculating the rate coefficient kD(J,K) for hitting collisions between ions and symmetrical top dipolar molecules in level (J,K) is formulated. The rate coefficient for a particular quantum level does not depend on the rotational constant A of the symmetrical top molecule. This facilitates parametrization of the results. Representative results on NH3 and CH3F including the thermal average k̄D are presented. A formula that Su and Chesnavich obtained for linear molecules reproduces k̄D for NH3 and CH3F quite well. Measured rate coefficients kr for reactive collisions between several species of ion and NH3 yield collision efficiencies kr/k̄D that are rather less than unity and temperature independent in the low temperature region. Corresponding results involving H2O suggest that the linear molecule formula is useful even for an asymmetrical top molecule.