Single-photon double ionisation of Isocyanic acid

Abstract

Isocyanic acid (HNCO), a molecule containing the four most abundant atoms of organic chemistry, has been studied by single-photon double ionisation. Both direct double ionisation, such as core-valence and valence-valence ionisation, and indirect double ionisation processes, such as the Auger effect, were studied by ionising the molecule with photons in the extreme ultraviolet and soft X-ray spectral region produced with lab based light sources and the synchrotron radiation facility BESSYII.

The spectroscopy method applied to these studies is based on a magnetic bottle electron spectrometer, by which the time-of-flight of the emitted electrons and their energy correlations were measured. For the Auger process, the photon energy is selected to be 20 eV above the threshold to ionise from the core shells of the molecule. The photon energies used to study the core-valence processes were selected so that there was sufficient energy to ionise a core and valence electron simultaneously. The onset energy of valence double ionisation was measured to be 32.0 eV with five resolvable peaks in the range 32.0-50.2 eV. The core-valence spectra are compared with the spectrum of single valence ionisation, while the onset of the Auger spectra are compared with the onset of the double valence spectra. These results motivate further experimental and theoretical studies into reactive, short-lived molecules.