Resonant enhancement in the valence orbital photoionization cross sections of xenon difluoride

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Abstract
The nature of the resonances observed in the valence molecular orbitals photoionization cross sections of XeF2 has been characterized using continuum multiple‐scattering (MS) Xα calculations. Analysis of the theoretical cross sections of XeF2 and a hypothetical F⋅⋅⋅F molecule with the same bond length in XeF2 reveals that there are at least three independent mechanisms governing the resonance features. Rather broad weak features at high kinetic energy (above 20 eV) are present in both the fluorine dominating 10σg and 3πg cross sections in XeF2 and in the corresponding 1πg and 3σg orbitals of F⋅⋅⋅F. Taken together with an EXAFS‐like treatment of the F⋅⋅⋅F molecule, there is strong evidence that these features are due to diffraction of the photoelectrons by the F atoms. The strong enhancement in cross section at ∼11 eV in the 10σg and 3πg orbitals are not present in the F⋅⋅⋅F orbitals, and are identified as shape resonances which are due to electronic excitations from these molecular orbitals to quasibound predominantly Xe kf (l=3) (kπu and kδu) continuum channels. The localization of the kf continuum is due to the trapping of the wave function by a barrier created by a centrifugal potential analogus to that in atomic Xe. The low energy resonances (kπg and kδg) around 4.8 eV above the ionization threshold are assigned to excitations into valence–Rydberg (d) mixed continuum channels.