Core to valence transitions in methane

Abstract

We have identified and characterized 1a 1 core electron transitions to states involving the anti-bonding 2t 2 σ * virtual orbital in methane. The 1t 2 autoionization branching ratio indicates that the excitations lie at the same energies as the Rydberg resonances observed in total absorption. The corresponding 1t 2 angular distribution parameter reflects coupling of electron and nuclear coordinates. Changes in the 1t 2 kinetic energy distribution are explained by nuclear motion during the core-hole lifetime due to repulsive potential energy surfaces. The data indicate that 1a 1 core-excited states involving the valence 2t 2 σ * molecular orbital are split by the Jahn–Teller effect into bands which are much broader than any Rydberg features. These results illustrate the value of valence emission as a probe of resonant molecular core-excited states.