Photoionization from Outer Atomic Subshells. A Model Study

Abstract

Calculations of photoionization cross sections are reported which emphasize the spectral range (from threshold to 150 eV above it) where the bulk of the optical oscillator strength is distributed and where the cross sections are large but experimental evidence is scarce. We have used as a model the light absorption by a single electron moving in a potential similar to the Hartree-Fock potential appropriate to the outer subshell of each atom. Data are reported for the rare gases He, Ne, Ar, and Kr, for Na, and for the closed-shell ions Cu+ and Ag+. Sum rules are used to analyze the oscillator strength spectral distribution and to attempt extrapolations to still higher energies. The results suggest a classification of atomic subshells into two types with fundamentally diferent spectral distributions of oscillator strength. One type consists of the subshells 1s, 2P, 3d, 4f, with nodeless radial wave functions, the other type includes all remaining subshells. The present calculations are regarded as a first approximation to be improved upon by taking into account configuration interaction.

Retrieval of the amplitude and phase of the dipole matrix element by attosecond electron-wave-packet interferometry

“…and the phase exhibits a phase jump by π at this final momentum. This behavior is similar to that found around the Cooper minimum in photoionization of argon [30]. The sequence of pulses is shown in Fig.…”

Exterior complex scaling method in time-dependent density-functional theory: Multiphoton ionization and high-order-harmonic generation of Ar atoms

“…On the contrary, the TDDFT spectrum contains comparable contributions from different Kohn-Sham spin orbitals thus indicating the significance of multielectron effects. Both frozen-core model and TDDFT spectra have a minimum in the central part which is closely related to the Cooper minimum [31] observed in the photoionization cross sections of Ar. This minimum originates from the nodal structure of the 3p wave function of Ar which causes the bound-continuum 3p − Ed dipole matrix element to vanish at some energy E in the continuum [31].…”

“…Both frozen-core model and TDDFT spectra have a minimum in the central part which is closely related to the Cooper minimum [31] observed in the photoionization cross sections of Ar. This minimum originates from the nodal structure of the 3p wave function of Ar which causes the bound-continuum 3p − Ed dipole matrix element to vanish at some energy E in the continuum [31]. According to the three-step model of HHG [32], the third step of this process is recombination of the recolliding electron with the core.…”

Valence and L-shell photoionization of Cl-like argon using R-matrix techniques

“…This densely populated region of Rydberg resonances up to approximately 30eV is followed by a steep decline in the photoionization cross section forming the expected Cooper minimum around 45-50eV. This minimum is well known to appear in the spectra of noble gases (Cooper 1962 Photoionization cross section (log(Mb)) monotonically decreasing towards zero with increasing photon energy.…”