Identification of Free Radicals in Flash Photolysis

Abstract

In our previous communication¹ we gave an account of experiments on the flash photolysis of cyanogen/oxygen and cyanogen/ozone mixtures in which a new transient band system was obtained in absorption in the wavelength region 3250–3330 Å. Although the rotational structure of the band system could not be resolved because of the low dispersion used, the chemical and kinetic evidence obtained from these and related experiments indicated that the most likely absorbing species was the free fulminate radical (C—N—O). This same spectrum has recently been obtained by Herzberg and Travis² also by flash photolysis, using diazomethane and diazomethane/cyanogen mixtures. These authors were able to carry out a vibrational and rotational analysis of the band system and from their observations have concluded that the absorbing species is NCN. This conclusion of Herzberg and Travis is substantiated by their carbon isotope experiments showing the presence of one carbon atom and the observation of an intensity alternation indicating the presence of two identical nuclei of non-zero spin. The observed triplet splitting is also consistent with the assignment of the absorber to NCN. However, these workers have not attempted to give any kinetic mechanism for the formation of the NCN radical in their systems and did not carry out any isotopic experiments to disprove the presence of oxygen.