Multielectron photoionization to the3p44pconfiguration ofAr+

Abstract

Short-pulse (100-psec) soft-x-ray excitation from a laser-produced plasma and fast optical detection have been used to study multielectron photoionization from the 3p neutral ground state to the ten terms of the 3p 4p configuration of Ar+. Good agreement between measured populations and those obtained from an excitation model based on energy-dependent cross sections calculated with a relativistic Hartree-Fock atomic physics code using configuration interaction techniques was obtained.A 100-psec duration soft-x-ray pulse from a laserproduced plasma combined with a subnanosecond optical detection system has been used to study electron correlations in Ar by observing multielectron photoiomzation from the 3ps ground state of neutral Ar to the 3p 4p configuration of Ar+. Measured population densities of the ten LS terms of this configuration produced by direct two-electron photoionization are in reasonably good agreement with those predicted by an excitation model based upon calculated photoionization cross sections to these ten terms and a measured soft-x-ray flux equivalent to an approximately 23-eV blackbody.The energy-dependent cross sections were computed with an atomic physics code using configuration interaction (CI) techniques. The sum of two of the calculated partial cross sections, with a peak value of 0.06 Mb at 40 eV (310 A), agrees within 30% over a wide range of energies with a cross section for those terms deduced from satellite intensities measured with photoelectron spectroscopy. When atoms are photoionized, observation of secondary processes involving excitation of more than one electron can be used to interpret the nature of the coupling or correlation between the electrons of the atom, not only in their initial and final states but also in the dynamics of the readjustment during the electron departure. Secondary photoionization can occur as a result of three processes The first is the "shake" type of process~dominant at higher energies. The second is the result of electron correlations in the initial and final ionic states giving rise to configuration interactions. The third is interchannel coupling which results from interactions between various final states by means of the continuum. The present investigation involves studies of the second process, the effect of electron correlations.Evidence of secondary processes were first observed in absorption spectroscopy3 but were often obscured by the primary one-electron processes. In many atoms secondary processes have been studied with photoelectron spectroscopy through the presence of sateIlite lines in the photoelectron spectrum. However, in cases w'here there are a large number of closely spaced excited states, identification is not possible either because of low resolution or because of the presence of other background emissions. Because the experimental technique described in this Rapid Communication monitors the emission from the various multielectron excited states immediately after the excitation terminates, before cascade or electron collision...

Many-electron dynamics of atomic processes studied by photon-induced fluorescence spectroscopy

“…Calculations of the σ(np 4 mℓ) PICS for satellites were practically absent. Silfvast et al (1986) computed the PICS for the Ar odd 3p 4 np satellites production considering the 3p 6…”

“…Calculations of the σ(np 4 mℓ) PICS for satellites were practically absent. Silfvast et al (1986) computed the PICS for the Ar odd 3p 4 np satellites production considering the 3p 6 3p 4 npε(s/d) transition of the 'shake' type. The influence of resonances on the computed PICS had not been included.…”

Use of partial-wave decomposition to identify resonant interference effects in the photoionization–excitation of argon

“…Theoretical estimates of the direct production cross sections for the 3p 4 ( 3 P) 4p states imply that they should be much less important in this energy range than resonant processes [22,27,28]. Indeed, there is no readily identifiable 'smooth' underlying background in any of these spectra, with the possible exception of the reactions (1) and (2) 2 P spectra above 36.26 eV, and the reaction (6) 4 D 5/2 spectrum above 36.07 eV.…”