The pattern of electron correlations is examined for odd-parity L =1 states of calcium over a wide range of energies from far below the 4s threshold up to the 4p threshold of Ca+. By combining quantum-defect theory with a small-scale eigenchannel R-matrix calculation, good agreement with the observed photoabsorption spectrum is obtained. The two-electron probability densities and channel-interaction parameters are analyzed as functions of the total energy. A novel interference between direct (4scp-3dcp) and indirect (4scp-4pcs-3dcp) channel-interaction amplitudes greatly reduces the width of the 3d 6p autoionizing resonance compared to adjacent series members.

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%e have calculated the total energy loss of an incident electron or positron due to the bremsstrahlung radiation from various atoms during a scattering. The kinetic energies considered for the incident electrons and positrons were 10, 50, and 500 keV. The calculations were performed with our relativistic partial-wave multipole-expansion numerical code [H. K. Tseng and R. H. Pratt, Phys. Rev. A 3, 100 (1971)]. The differences between the radiative energy loss of positrons and electrons are considerable and cannot be disregarded. %e observe that the ratio of the radiative energy loss for positrons to that for electrons obeys a simple scaling law, being expressible fairly accurately as a function only of the quantity Tl /Z, where Tl is the incident-particle kinetic energy and Z is the atomic number of the scatterer. This scaling law makes it possible to obtain the energy loss for positrons from existing electron bremsstrahlung data. The scaling is exact in the case of the point Coulomb potential, both in the classical bremsstrahlung formula and the nonrelativistic dipole Sommerfeld formula, not only for the ratio of total energy losses but also for the separate energy losses and even for the radiation energy spectrum. In the screened case scaling is significantly broken for the spectrum and for the total energy loss but remains fairly good for the ratio of the total energy losses. %e will discuss scaling features of bremsstrahlung radiation energy loss and the behavior for both high and low energies.

Strontium, barium and radium are predicted to have stable negative ions of ns2np designation, on the basis of eigenchannel R-matrix calculations performed in LS coupling for the negative ion of each alkaline-earth atom. The calculations also confirm earlier studies indicating that the negative ion of calcium is stable and that corresponding 2P degrees states in beryllium and magnesium are unstable shape resonances. The much larger polarisability of the heavier alkaline earths play a crucial role in binding the additional electron. The analysis uses quantum defect theory in its generalised form appropriate for long-range motion in a dipole polarisation potential.

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