Argon-induced halfwidths and line shifts of water vapor transitions

Abstract

Pressure-broadened halfwidths and pressure-induced line shifts are determined for water vapor transitions with argon as the perturbing gas. Calculations based on the complex Robert–Bonamy (CRB) formalism are made for a number of vibrational bands, for which there are experimental data to compare with. The intermolecular potential is taken as a sum of Lennard–Jones (6–12) atom–atom, isotropic induction, and dispersion components. The dynamics of the collision process are correct to second order in time. The calculations demonstrate that the atom–atom potential for this system should be expanded to 12th order. A new feature in the CRB approach is that the real and imaginary components of the Liouville S matrix affect both the halfwidth and the line shift. It is shown here that the imaginary parts of the S matrix strongly affect the calculated H 2O–Ar halfwidths. The calculated values are compared with those obtained in a number of experimental studies. In general, good agreement is observed between the CRB calculations and the measured values for both halfwidths and line shifts. It is also clear that some parameters describing the intermolecular potential need to be better determined.