Collision broadening and shift in the resonance line of calcium

Abstract

The broadening and shift of the calcium resonance line, lambda 4227 angstroms, have been measured with high accuracy when the line is formed in absorption under pressures of He, Ne, Ar, Kr, and Xe up to one atmosphere. He and Ne cause symmetrical broadening over the entire pressure range in agreement with the predictions of the 'impact theory'. The onset of asymmetrical broadening indicating breakdown of the 'impact approximation', is noticed at pressures of Ar, Kr, and Xe close to one atmosphere. The peculiar way in which broadening and shift change with perturbing gas is discussed in terms of 6-12 and 6-8-12 interatomic potentials.