The dissociation energies of CO, N 2 , NO and CN

Abstract

No previous set of values of the dissociation energies of CO, N 2 , NO and CN can be regarded as satisfactory unless violations of the non-crossing rule are postulated as possible. The Birge-Sponer method of extrapolating vibrational energy levels to the dissociation limit is discussed. By assuming that the intensity variations in the Fourth Positive bands of CO, usually regarded as due to a predissociation, are really perturbations, and by adopting an alternative interpretation to the commonly accepted one for the predissociation in the First Positive bands of N 2 , it is possible to reconcile existing data with both the non-crossing rule and the Birge-Sponer extrapolations only with the following values D (CO) = 11.11 eV, D (N 2 ) = 9.764, D (NO) = 6.49, D (CN) = 7.5. The corresponding value of the latent heat of sublimation of carbon is 170.1 kcal./mol. This scheme of values explains the results of related experimental measurements at least as well as any other.