Photoionization and electron-impact ionization of Yb atoms from an excited aligned state

Abstract

The multiconfiguration Hartree–Fock (MCHF) and the plane-wave Born approximations (PWBA) based on Dirac–Fock multiconfiguration (MCDF) computations are used to calculate the photoionization cross section and electron-impact ionization cross section of Yb from the 6s6p 3P1 state, respectively. The wavefunctions of open-shell systems were modelled by Hartree–Fock Slater and Dirac–Fock Slater nonorthogonal orbitals with allowance for the relaxation effects. The one-electron wavefunction of the continuous spectrum for the photoelectron and for the ejected electrons was obtained using single-configuration Hartree–Fock and Dirac–Fock methods, respectively. The orthogonalization of the ejected and photoelectron wavefunctions to all occupied orbitals of the target atom is performed. The calculations of the cross sections for electron-impact ionization based on MCHF and MCDF approximations are compared with each other. The ratio of the reduced dipole matrix elements and the phaseshift difference for transition 6pεs and εd are first compared with available polynomial fitting of the experimental photoelectron angular distribution data from laser-excited aligned Yb* atoms ionized by vacuum ultraviolet radiation.