First ionization potential of the FCO (X2A′) radical studied using photoelectron spectroscopy

Abstract

Vacuum ultraviolet photoelectron spectroscopy has been used to detect the fluoroformyl radical in the gas phase. FCO was formed by the atom–molecule reaction F + HFCO → HF + FCO. (1) Both He I and Ne I spectra have been recorded of the band associated with the lowest energy photoionization process. Extensive vibrational fine structure characteristic of the (FCO⁺) deformation vibration was observed. Analysis of this fine structure gave a value [graphic omitted]_e= 650 ± 30 cm^–1. The vertical ionization potential was measured as 11.26 ± 0.01 eV but evidence is presented to show that the adiabatic ionization potential was not directly observed. A Franck–Condon calculation allowed this ionization potential to be determined as 8.76 ± 0.32 eV. This assignment is supported by ΔSCF ab initio molecular orbital calculations with allowance for the correlation energy change on ionization. Use of this new value for the adiabatic ionization potential together with the established heat of formation of the fluoroformyl radical allows a more accurate derivation of the heat of formation ΔH^⊖_f(298)(FCO⁺) as 669 ± 46 kJ mol^–1.