Simple Potential Functions and the Hydrogen Halide Molecules

Abstract

Five simple molecular potential functions have been tested by comparison with spectroscopic data for the hydrogen halides. It is shown that when plotted on a ``reduced'' distance scale (r/re), the potential curves for these molecules coincide closely up to Δ(r) = 0.10re. Two electrostatic functions indicate β/rn as the more satisfactory form of the repulsive term. Significant values of the effective polarizability and ``fractional ionic character'' are deduced. The latter are higher and more nearly constant than the uncorrected values currently quoted as showing changing bond type in these molecules. The results conform with Kirkwood's very successful treatment of HCl as a polarizable ion pair. Of purely empirical functions, the Pöschl-Teller provides a slight improvement upon the simple Morse relation, and is only a little more cumbersome than the latter. The Rosen-Morse function is less satisfactory for these molecules. Simple expressions are given for evaluating the three parameters in these functions from spectroscopic data.