Accurate non-relativistic photoionization cross section for He at non-resonant photon energies

Abstract

The total single-photon ionization cross section was calculated for helium atoms in their ground state. Using a full configuration-interaction approach the photoionization cross section was extracted from the complex-scaled resolvent. Our results agree with an earlier B-spline-based calculation in which the continuum is box discretized within a relative deviation of less than 0.06% in the energy range from 28 to 59 eV. On the other hand, above the He++ threshold our results agree very well to a recent Floquet calculation. Thus, our calculation confirms the previously reported deviations from the experimental reference data outside the claimed error estimate. In order to extend the calculated spectrum to very high energies, an analytical hydrogenic-type model tail is introduced that should become asymptotically exact for infinite photon energies. Its universality is investigated considering also H−, Li+ and HeH+. With the aid of the tail corrections to the dipole approximation are estimated.