Direct probe of the shape resonance mechanism in 2σg-shell photoionization of the N2 molecule

The angular distribution of photoelectrons (ADPs) for the 2σg shell of fixed-in-space N2 molecules was measured by the angle-resolved electron-ion coincidence technique using elliptically and linearly polarized light. The set of measured data was sufficient for extracting the ratios of dipole matrix elements and phase shift differences corresponding to four main continuum channels, Εpσu, Εfσu, Εpπu, and Εfπu, assuming the validity of a single-particle description. By normalization to the experimentally measured partial cross section, it was possible to deduce also the absolute values of the matrix elements. It was shown that the main contribution to the photoionization cross section in the resonance is given by the fσu partial wave, with the phase shift difference increasing in that region by π radians.