Photoionization of HCN: The Electron Affinity and Heat of Formation of CN

A re-examination of the photoionization of HCN has revealed two processes, HCN + hν→H + +CN−, and HCN + hν→H + +CN+e, not previously reported. The difference in threshold values for the two processes leads directly to the electron affinity for CN, 3.82 ± 0.02 eV. The threshold for the second process leads to ΔHf0°(CN) = 105.5 ± 2 kcal/mole, but ΔHf°(HCN) remains a major source of uncertainty.