Molecular effects on inner-shell photoabsorption. K-shell spectrum of N2

Abstract

K-shell photoabsorption spectra of the first-row diatomic molecules N2, CO, and NO are known to depart drastically from the behavior characteristic of K-shell excitation in atoms. Below the K-shell thresholds these spectra are dominated by a single, very intense peak rather than normal Rydberg structure, and the first 10–20 eV of the continuum exhibit a broad band of enhanced absorption, rather than a monotonic decrease. We use the multiple-scattering model to compute the discrete part and the first 100 Ry of the photoionization continuum for K-shell photoionization of N2. This calculation accounts for both novel features described above and shows that they arise from centrifugal barrier effects manifested as shape resonances in high-l components of the final state wavefunctions. These effects are molecular in origin, resulting from the interaction between the photoelectron and the anisotropic molecular field. We also discuss the energy dependence of the photoelectron angular distributions, Kronig structure in the high-energy continuum, bearing of the present results on valence-shell spectra, and the likelihood of widespread observation of shape resonances in ionization processes in other molecules.