Binary Collision Broadening: Approximate Methods

Abstract

The difficulties associated with the determination of potential parameter estimates for excited electronic states from the shift and width of isolated electronic spectral lines within the impact limit are discussed and analyzed. Using the LJ potential as a model, the measured shift and width of the He–Kr system are compared to exact theoretical calculations generated from quantum and JWKB phase shifts over an extended velocity region. A detailed, but easily understood, velocity dependence is found. The effect of thermal averaging is discussed, and two new approximations using variants of the Massey—Mohr and stationary-phase approximation are developed and compared to the exact results. The relationship of the exact calculations, the new approximations, thermal averages, and many of the previously used approximations is examined in detail.