Some transition moments via perturbation methods for the helium isoelectronic series

Abstract

Transition moments for the strongly allowed (21P, 11S) and for the (23P, 23S) transitions in the helium isoelectronic sequence are computed from tenth-order perturbation wave functions using the length, velocity, and acceleration forms of the requisite operator. In addition, more limited results for transitions from NP states are also considered. The internal consistency as well as the absolute values of the results are in satisfactory agreement with the results of C. L. Pekeris and coworkers based on total variational wave function calculations, and hence in agreement with experiment. Since the 23P and 23S states are degenerate in zero order, it turns out that the first four expansion coefficients for the expectation value of the acceleration form of the operator must be calculated as zeroes from the perturbation expansion of the wave function, thus furnishing an absolute indication of the accuracy of that part of the calculations.