EPR study of NO2 and NO3 produced in urea nitrate by uv irradiation, x-irradiation, and constituent tritium atom decay

Abstract

NO2 and NO3 radicals have been produced by uv irradiation, x-irradiation, and constituent tritium atom decay in single crystals of urea nitrate. Two types of NO3 and five types of NO2 were produced, and which of these were observed depended on the type of irradiation and the temperature. At 77 °K two types (two different orientations) of NO2 were formed from tritium decay while only one of these was produced by x-irradiation. The various forms of NO2 were found to irreversibly interconvert from one to another as the temperature increased. Different mechanisms for defect formation have been proposed to account for the different types of radicals formed by x-irradiation and tritium decay at room temperature and 77 °K. The NO3 species which resulted from any of the methods of irradiation at room temperature showed no 14N hfs but did exhibit a significant interaction with five neighboring hydrogen bonded protons. Deuterium substitution caused the proton hfs to collapse into one line, thus simplifying the analysis. This NO3 was the same one reported formed by γ-irradiation. A different type of NO3 without proton hfs was formed when either x-irradiation or tritium substitution was used at 77 °K. These two types did not interconvert. From evaluation of the spin-Hamiltonian parameters the electronic ground states for these NO3 radicals have been elucidated. The low temperature form is found to be a π radical and the high temperature form is a σ radical.