The first ionization potential of the formyl radical, HCO(X2A′), studied using photoelectron spectroscopy

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Abstract
A partial HeI photoelectron spectrum of the formyl radical has been obtained. In the band associated with the first ionization potential a long vibrational series was observed for both HCO and DCO and analysis of the vibrational structure, which is attributed to excitation of the deformation vibration in the ion, gave values of and 620 ± 30 cm-1 in the HCO and DCO cases respectively. For HCO the first vertical ionization potential has been measured as 9·31 ± 0·01 eV. Evidence is presented to show that the formyl radical provides an example of a rare case in photoelectron spectroscopy where the adiabatic ionization potential is not directly observed. However, with the aid of Franck-Condon calculations, the first adiabatic ionization potential of HCO is estimated as 8·27 ± 0·01 eV. Use of this value allows the heat of formation of HCO, ΔH ⦵ f(298) (HCO) and the C-H bond dissociation energy in formaldehyde to be calculated as 28·0 ± 5·4 kJ mol-1 and 354·0 ± 6·3 kJ mol-1 respectively.