The impulse approximation for the broadening of Mg I infrared lines by collisions with neutral hydrogen

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Abstract
The broadening of infrared lines, resulting from transitions between high nl levels, with l=n-i or n-2, is due to the l-mixing collisions, induced by the Rydberg electron-hydrogen interaction. Validity conditions of the impulse approximation are discussed, and two methods, derived from the form factor formalism and from the free electron model, are applied to the study of the two most prominent magnesium lines observed in the solar spectrum: 6h-7i at 811.58 cm-1 and 6g-7h at 818.05 cm-1. Owing to the large abundance of hydrogen in the solar photosphere, their widths gamma H are found to be comparable to gamma c due to electron collisions.