Coincident velocity map image reconstruction illustrated by the single-photon valence photoionisation of CF3SF5

Research output: Contribution to journalArticle

Authors

Colleges, School and Institutes

External organisations

  • Laboratory for Synchrotron Radiation and Femtochemistry, Paul Scherrer Institute

Abstract

Velocity map imaging offers high energy resolution and collection efficiency of the steady flux of photoelectrons and ions in continuous photoionisation experiments. In this proof-of-principle work, we show by the example of trifluoromethyl sulphur pentafluoride, CF3SF5, that the four-dimensional problem of reconstructing coincident velocity map images of electrons and ions of certain mass can be addressed by separating the energy distribution from the angular anisotropy. The energy spectrum is predominantly determined by the radial distribution of the image, whereas laboratory frame angular anisotropies are revealed based on the radial distribution of the image multiplied with a 2nd-degree Legendre polynomial. The reconstruction yields the energy correlation between the photoion and the photoelectron characteristic of the photoelectron spectrum and the kinetic energy release. The angular anisotropy β-parameter maps of the photoelectrons and photoions are also obtained as 2D functions of the electron and ion kinetic energies. For photoionisation of CF3SF5, the energy correlation reveals suprastatistical kinetic energy release (KER) in CF3+ production in the ground cationic X ̃^+ state, but statistical KER in the excited A ̃^+ and B ̃^+ state bands. Although the photoelectron distribution is isotropic, the photoion anisotropy in the energy range of the X ̃^+ state speaks for prompt dissociation after preferential ionisation of CF3SF5 molecules aligned with the polarisation vector of the synchrotron radiation. The angular dependence of the photoionisation cross section is confirmed by ab initio calculations for vertical ionisation.

Details

Original languageEnglish
Pages (from-to)30173-30180
JournalPhysical Chemistry Chemical Physics
Volume19
Early online date30 Oct 2017
Publication statusE-pub ahead of print - 30 Oct 2017