Fig. 1
From: Ultrafast isomerization in acetylene dication after carbon K-shell ionization
Illustration of relevant dynamical processes after core ionization of acetylene. a Sketch of the acetylene dication dynamics induced by X-ray photoionization and Auger decay. A first X-ray pump pulse core ionizes the neutral molecule to create the cation, which then undergoes Auger decay. A second X-ray probe pulse with a variable delay further core ionizes the dication, which promptly undergoes further Auger decay and Coulomb explosion. The momentum of the resulting fragments is measured to create the momentum map described in the text. b The potential curves of the singlet dicationic states are plotted in the adiabatic representation. The first 3 adiabatic states S0–S2 are dominated by a double hole configuration \(1\pi _{\rm{u}}^{ - 2}\), and the higher-lying S3 and S4 states have the double hole configuration \(1\pi _{\rm{u}}^{ - 1}3\sigma _{\rm{g}}^{ - 1}\), with one electron hole in each of the π- and σ-orbitals. The black arrows label the barrierless fragmentation pathway on S3/4, arising from a crossing of the diabatic states \(^1{\prod _{\rm{u}}}\left( {{{1}}\pi _{\rm{u}}^{ - 1}3\sigma _{\rm{g}}^{ - 1}} \right)\) and \(^1{\sum _{\rm{u}}}\left( {{{1}}\pi _{\rm{u}}^{ - 2} + {\pi _{\rm{u}}} \rightarrow \pi _{\rm{g}}^*} \right)\)
