2S1states of the helium isoelectronic sequence

Abstract

We propose a simple analytic wave function for the 1s2s 'S state of the two-electron atomic system. This is orthogonal to the ground-state function of Morse et al. The wave-function parameters are evaluated by the method of variational calculation for the eigenenergy. Using the present 2'S-state function we have calculated the values of the physical quantities mean square radius and scattering cross section in a few cases.We compare these with the relevant values that are available using many-parameter wave functions and obtain good agreement.