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

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Abstract
Total absorption method has been applied to determine broadening rates for 4 s 2 1 S 0 -4 s n p 1 P 1 (6≤ n ≤17) and 4 s 2 1 S 0 -3 d 4 p 1 P 1 in calcium in the presence of helium. A maximum rate coefficient of 1.75×10 -8 cm 3 s -1 occurs for 4 s 2 -4 s 7 p . The admixture of 3 d 4 p configuration with the 1 P 1 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.