Mass-Spectrometric Study of Photoionization. IX. Hydrogen Cyanide and Acetonitrile

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 ${\mathrm{\Delta Hf}}_0\text{°(CN)\hspace{0.17em}=\hspace{0.17em}100}{\mathrm{kcal\; mole}}^{\text{−1}}$ , $D_0\text{(CN)\hspace{0.17em}=\hspace{0.17em}182.5}{\mathrm{kcal\; mole}}^{\text{−1}}$ , $D_0\text{(H–CN)\hspace{0.17em}=\hspace{0.17em}119.2}{\mathrm{kcal\; mole}}^{\text{−1}}$ , and $D_0\text{(NC–CN)\hspace{0.17em}=\hspace{0.17em}126.6}{\mathrm{kcal\; mole}}^{\text{−1}}$ . 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 ${\mathrm{\Delta Hf}}_0{\mathrm{°(CH}}_2\text{)\hspace{0.17em}=\hspace{0.17em}94}{\mathrm{kcal\; mole}}^{\text{−1}}$ .