Pressure Broadening of theO2Microwave Spectrum

A general expression for the calculation of pressure broadening for vibrational-rotational lines is derived in the strong-collision model. Classical trajectories and a peaking approximation are used to calculate a unitary scattering operator avoiding perturbation expansions, impact-parameter cutoffs, and straight paths. The latter approximations are not expected to be good when short-range potentials dominate the collision interaction. Use of intermolecular-potential parameters determined from thermodynamics and a simple theory of dispersion forces for ${\mathrm{O}}_2$ calculations gave excellent agreement with experimental data on the magnitude, temperature, and quantum-number dependence of the linewidth parameter.