Core to valence transitions in methane

We have identified and characterized 1a1 core electron transitions to states involving the anti-bonding 2t2 σ* virtual orbital in methane. The 1t2 autoionization branching ratio indicates that the excitations lie at the same energies as the Rydberg resonances observed in total absorption. The corresponding 1t2 angular distribution parameter reflects coupling of electron and nuclear coordinates. Changes in the 1t2 kinetic energy distribution are explained by nuclear motion during the core-hole lifetime due to repulsive potential energy surfaces. The data indicate that 1a1 core-excited states involving the valence 2t2 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.