A study of the valence shell spectroscopic and thermodynamic properties of trifluoronitrosomethane cations

Abstract

A time-of-flight mass spectrometry study has been carried out to investigate the fragmentation processes occurring in trifluoronitrosomethane (CF3NO) as a result of valence shell photoionisation. Synchrotron radiation has been used to record spectra in the photon energy range ∼10–42eV, and appearance energies have been determined for 10 fragment ions. At high excitation energies, singly charged atomic fragments have been observed. For the main dissociation channels, leading to the formation of NO+, CF2+ or CF3+, the experimental appearance energies have been compared with thermochemical estimates, and a satisfactory agreement has been found. Structure observed in the total ion yield curve has been interpreted with the aid of excited state transition energies and oscillator strengths obtained in a time-dependent Hartree Fock calculation. The theoretical results show that configuration interaction strongly affects many of the valence states. A HeI excited photoelectron spectrum of CF3NO has been measured and the orbital ionisation energies have been compared with theoretical values computed using the Outer Valence Green’s Function approach. A large Franck–Condon gap is observed between the X˜2A′ and the A˜2A′ state bands, in accord with the calculated vertical ionisation energies of 10.87 and 16.32eV for the 12a′ (n−) and the 11a′ (n+) orbitals, respectively. In the ion yield curve, the corresponding energy range is strongly influenced by autoionising valence states.