AN EXPANSION METHOD FOR CALCULATING ATOMIC PROPERTIES. X. (1S2 SINGLET S)-(1s np SINGLET P) TRANSITIONS OF THE HELIUM SEQUENCE,

摘要

The electric dipole matrix elements connecting the 1s2singlet S and 1s np singlet P states of the helium isoelectronic sequence are calculated exactly to first order in inverse powers of the nuclear charge Z and the differences in the Hartree-Fock approximation are shown to correspond to virtual transitions of the 1s electrons. Comparison of the oscillator strengths predicted by a screening approximation with more accurate values reveals a regular variation in the error contained in the screening approximation,the correction of which allows the prediction of oscillator strengths and probabilities of 1s2singlet S-1s np singlet P transitions for all values of n and all values of Z within a probable error of 2%. Values of the photoionization cross sections at the spectral heads are also presented. (Author)