There are very few experimental measurements against which these results can be compared. The electron/ion coincidence spectroscopic data of Schwell et al. yielded 9.71 eV for acetamide as against a computed 9.70 eV but for N-methyl formamide the calculated value of 9.79 eV is wildly at odds with the 9.55 eV obtained in a photoionisation mass spectrometric study by Leach and co-workers. In addition atomisation energies and consequently formation enthalpies at 0 K were tabulated, Table , and compared to the higher level results in Tables 2-3 by means of a Bland-Altman 90 plot, Fig. . The bias, that is the average deviation of G4 from the higher level methods is a modest 0.39 kJ mol -1 . The most obvious deviations are shown by the nitrenes in their triplet state, Fig. , which is not totally unexpected.