New insights on the shape resonances in the K-shell continua of the N2 and CO prototype molecules

Abstract

We have re-examined the shape resonances of N 2 and CO both experimentally and theoretically at the profound level of the photoelectron angular distribution from fixed-in-space molecules, from which one can extract the dipole matrix elements and the phase differences describing the photoionization processes. For N 2 , we have obtained a remarkable result, i.e., the σ * shape resonance enhancement appears not only in the 1 σ g → ϵσ u channel but also in the 1 σ u → ϵσ g channel due to the intershell interaction between the 1 σ g and 1 σ u molecular orbitals, in contrast to the results of single particle calculations. For CO, we have derived the dipole matrix elements and the phase differences in the σ * shape resonance regions in the C- and O–K shell ionization continua. They demonstrate that the σ * shape resonance above the C–K edge consists of p -, d - and f -partial waves and the resonance above the O–K edge consists of s -, p -, d - and f -partial waves, in contrast to the widely accepted idea that only the f -partial wave is enhanced.