On the heat of formation of diimide

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Abstract
The heat of formation of trans‐diimide (N2H2) has been determined mass spectrometrically by combining the ionization potential of N2H2 with the appearance potential of N2H+2 in the reaction N2H4+e→N2H+2+H2+2e. The measurements are I.P.(N2H2) =9.65±0.08 eV, in agreement with the photoelectron spectroscopic value, and A.P.(N2H+2) =10.75±0.08 eV leading to ΔH°fo(N2H2) =52.4±2 kcal/mole and ΔH°f298(N2H2) =50.7±2 kcal/mole. Studies of the reaction N2H4+e→N2H+2+2H+2e have provided confirmatory information on this energy assignment and suggest that excess energy in these reactions is very low or zero. The results on the heat of formation of diimide are in good agreement with our earlier work and in remarkable concordance with recent theoretical calculations, but are in marked disagreement with a very recent determination using data from the reaction N2H2+e→N+2+H2+2e. We have been unable to confirm the experimental results reported for this reaction. The measured value of ΔH°fo(N2H2) together with some auxiliary data allows the calculation of several important N–N and N–H bond dissociation energies.