Argon 3sautoionization resonances

Synchrotron-radiation excited ion mass spectrometry has been used to study the 3s3p⁶np(n{≥}4) resonances in argon at 25.0--29.3 eV. It is shown using a time-independent resonant scattering approach that the Fano parametrization may be applied to overlapping resonances. For the Dubau-Seaton profile an exact expression of the closed-channel phase shift is obtained. We find that regarding the window character of the Ar 3s series the Fano parameters calculated using the multichannel multiconfiguration Dirac-Fock method are in good agreement with those derived from fitting a convoluted Fano function to the measured n=4 autoionizing resonance. The Fano parameters are also derived from perfect fits to the 5{≤}n{≤}8 resonances which tests the validity of this parametrization to overlapping members of an inner-valence electron resonance series. In contrast, a parametrization of the entire series based upon the Dubau-Seaton formula did not result in a good fit without modifications. Using the same value of the shape parameter we find, however, that the n=4 resonance can be accurately represented by both the Fano and Dubau-Seaton profiles.