Photoionization yield curves are obtained from threshold to 600 Å for the HCN+ and CN+ ions of HCN and for the principal ions of CH3CN. The first ionization energy of HCN is 13.59 eV. The threshold for the CN+ ion permits calculation of ΔHf0°(CN) = 100 kcal mole−1, D0(CN) = 182.5 kcal mole−1, D0(H–CN) = 119.2 kcal mole−1, and D0(NC–CN) = 126.6 kcal mole−1. Dissociative photoionization processes in acetonitrile do not produce methyl or cyanogen radical ions in sufficient abundance for direct verification of the above. Nevertheless, threshold values of the principal photoions of CH3CN are tabulated, and some thermodynamic values are calculated, including ΔHf0°(CH2) = 94 kcal mole−1.

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