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

Total absorption method has been applied to determine broadening rates for 4s2 1S0-4snp 1P1 (6<n< 17) and 4 s2 XS0 - 2>d4p 1P1 in calcium in the presence of helium. A maximum rate coefficient of 1.75 x 108 cm3s-1 occurs for 4s2-4slp. 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.