Abstract
Theoretical investigations employing the recently devised Stieltjes-Tchebycheff procedure and variational calculations in Hilbert space are reported of the photoexcitation and ionization cross sections in atomic lithium. The calculations include orbital configurations corresponding to both valence and -shell electron excitations, allowing for core polarization and for configuration interaction in both the ground and excited states. Hylleraas correlation factors are employed to aid the convergence of the configuration-interaction expansions. The resulting discrete and continuum dipole spectra, and related dipole spectral sums, are in excellent agreement with previously reported polarized-orbital and many-body calculations, with the results of semiempirical investigations based on one-electron model potentials, with recent measurements of the static dipole polarizability, and with the results of a recent analysis of the experimentally determined numbers. Discrepancies between the theoretical and experimental photoionization cross section in the higher-energy valence region are attributed to systematic errors in the measured values, in accordance with previous observations. Although the Stieltjes-Tchebycheff technique is particularly suitable for studies of photoionization in molecular systems, the present results indicate that highly reliable cross sections are also obtained from the approach in applications to many-electron atomic systems when appropriate square-integrable wave functions are employed.
- Received 6 June 1977
DOI:https://doi.org/10.1103/PhysRevA.16.1513
©1977 American Physical Society