Photoionisation of neutral calcium

The R-matrix method as described by Burke and Taylor (1975) is applied to the photoionisation of neutral calcium from the 1 S e ground state. Configuration-interaction wavefunctions are used to describe the initial Ca state and final Ca + states. Total photoionisation cross sections are calculated for photon energies in the range 6.11 eV ( 2 S threshold of Ca + ) to 9.25 eV ( 2 P threshold of Ca + ) and are compared with the experimental measurements of Brown et al. (1973) and Connerade et al. (1980). A Cooper minimum is found just below the 2 D threshold of Ca + and its effect on the neighbouring series of Rydberg resonances is illustrated by a rapid change in the line profile indices, or q values, of these resonances as this minimum is crossed. LS coupling is used throughout.