Breakdown of the Independent Particle Approximation in High-Energy Photoionization

Abstract

The independent particle approximation is shown to break down for the photoionization of both inner and outer nᐉ ͑ᐉ . 0͒ electrons of all atoms, at high enough energy, owing to interchannel interactions with the nearby ns photoionization channels. The effect is illustrated for Ne 2p in the 1 keV photon energy range through a comparison of theory and experiment. The implications for x-ray photoelectron spectroscopy of molecules and condensed matter are discussed. [S0031-9007 (97)03382-6] PACS numbers: 32.80.Fb

Dramatic Nondipole Effects in Low-Energy Photoionization: Experimental and Theoretical Study of Xe5s

“…In addition, for dipole photoionization, interchannel coupling, which is simply configuration interaction in the continuum, has been shown to be important for most subshells of most atoms at most energies [15,16]; this work was contrary to the previous conventional wisdom that the independent-particle approximation (IPA) was generally valid away from thresholds. It had been suggested, however, that such interchannel coupling was not important in quadrupole photoionization channels [17], but recent theory has suggested that interchannel coupling can indeed be significant in quadrupole photoionization channels as well [14].…”

“…Experiments have shown the importance of nondipole effects in the 1-3 keV photon-energy region [8,9], in the hundreds-of-eV range [10], and, in one case, at 13 eV [11]. Concurrently, theory has predicted significant nondipole contributions to electron angular distributions for atomic valence shells down to threshold at a few tens of eV photon energy [12 -14].In addition, for dipole photoionization, interchannel coupling, which is simply configuration interaction in the continuum, has been shown to be important for most subshells of most atoms at most energies [15,16]; this work was contrary to the previous conventional wisdom that the independent-particle approximation (IPA) was generally valid away from thresholds. It had been suggested, however, that such interchannel coupling was not important in quadrupole photoionization channels [17], but recent theory has suggested that interchannel coupling can indeed be significant in quadrupole photoionization channels as well [14].…”

High-energy photoeffect

“…(We are using a system of units _ ¼ c ¼ 1:) The correlation effects enter in Eqs. (1) and (2) through the constants a nl : The leading 1=o 9=2 energy dependence of the total cross sections for l > 1 is completely due to inter-channel coupling (Dias et al, 1997), i.e it is a consequence of correlations. This represents strong modifications of the IPA results.…”

“…For example, the high-energy behavior of total cross sections for single ionization of a many electron atom (in its ground state) resulting in a vacancy in an nl subshell after absorption of a photon of energy o5m is (Dias et al, 1997;Hansen et al, 1999;Amusia et al, 2000; …”

The influence of valence excitations on spectral distribution of vibrational excitations associated with C 1s photoionization in the CO molecule

“…[19]). It is caused by off diagonal matrix elements in the basis of 'ion + continuum electron' eigenstates.…”