Photoionization and electron-ion recombination of He I

Results from the unified method for photoionization and electron-ion recombination of (HeI+hν↔HeII+e) are presented. He I wave function is represented by an expansion that includes 10 core states for excitations to n = 2, 3, and 4 states. A total of 99 bound LS states with n⩽10 are obtained. They all, except two, agree with the observed energies in less than 1%. Photoionization cross sections σPI for the total ionization, leaving the residual ion in all excited states, and the partial ionization, leaving the ion in the ground state, are presented for all 99 bound states. Calculated σPI agree very well with the measured ground state cross section. Detailed resonant features of σPI and coupling effects on the background cross sections are illustrated. For the recombination process, state-specific and total recombination rate coefficients are presented. These include both the radiative and dielectronic recombination processes. In addition, the total recombination spectrum with electron energy is presented and exhibits the resonant features that were observed experimentally. Recombination rates for hydrogenic He II is also presented. The present results obtained in LS coupling approximation provide a unified and self-consistent sets of results for astrophysical modelings of the two inverse radiative processes until highly accurate and precise results will be available through comprehensive relativistic calculations.