Collision Broadening of Principal Series Lines of Calcium in the Presence of Helium

Abstract

Total absorption method has been applied to determine broadening rates for 4s^{2 1}S₀-4snp ¹P₁ (6≤n≤17) and 4s^{2 1}S₀-3d4p ¹P₁ in calcium in the presence of helium. A maximum rate coefficient of 1.75×10⁻⁸ cm³s⁻¹ occurs for 4s²-4s7p. The admixture of 3d4p configuration with the ¹P₁ series does not induce any marked singularity. The measured rate coefficients are in good agreement with those calculated by the theory of Alekseev and Sobel’man for n≥12, but give larger values by a factor of 2 than those calculated by the theory of Omont for n≥8. These facts suggest that the inelastic scattering, neglected in the latter theory, contributes considerably to the broadening rates.