NSF PAR Search | NSF Public Access Repository

State selectivity in core ionization of methane

https://doi.org/10.1103/PhysRevResearch.7.L022021

Rajput, J; Stindl, J; Cassimi, A; Gervais, B; Kircher, M; Kastirke, G; McGinnis, O D; Enoki, R; Williams, J B; Davis, V; et al (April 2025, Physical Review Research)

A clear experimental signature of the population of the lowest triplet state

{}^{3}T_{1}

of the methane dication is identified in a photoionization experiment. This state is populated only in valence ionization and is absent when the dication is formed by core ionization followed by Auger-Meitner decay. For valence ionization, the total internal energy of the

{CH}_{3}^{+}

fragment, formed during the deprotonation of

{CH}_{4}^{2 +}

, is evaluated. Notably, the distribution of this internal energy peaks at the same value regardless of the initially populated electronic state of

{CH}_{4}^{2 +}

. We find that excited electronic states of

{CH}_{3}^{+}

are predominantly populated with significant rovibrational excitation. Published by the American Physical Society2025

Free, publicly-accessible full text available April 1, 2026

We use one-photon excitation to promote

K

-shell electrons of formic acid (which has a planar equilibrium structure) to an antibonding

π^{*}

orbital. The excited molecule is known to have a (chiral) pyramidal equilibrium structure. In our experiment, we determine the handedness of the excited molecule by imaging the momenta of charged fragments, which occur after its Coulomb explosion triggered by Auger-Meitner decay cascades succeeding the excitation. We find that the handedness of the excited molecule depends on its spatial orientation with respect to the propagation (or polarization) direction of the exciting photon. The effect is largely independent of the exact polarization properties of the light driving the

1 s \to π^{*}

excitation. Published by the American Physical Society2024

Search for: All records