Mass-polarization effect and oscillator strengths forS,P,Dstates of helium

It is well known that including the coordinate $r_{12}$ in the wave function is essential in obtaining highly accurate results for the low-lying bound states of two-electron systems. In this work we calculate the energy, wave function, oscillator strength, radial expectation values, and mass-polarization effect for helium bound states by using simple configuration-interaction basis functions. Our results show that the advantage of the $r_{12}$ coordinate is lost quickly in going from $S$ to $D$ states. In most cases, the results of this work give substantial improvement over previous calculations where $r_{12}$ is not included. For ${}_{}{}^{1,3}{}_{}{}^{}D$ states the results presented here are among the best in the literature.