Formation of Paramagnetic Species in Sodium Nitrite irradiated at Room Temperature

Abstract

RECENTLY both optical and electron spin resonance of single crystals of sodium nitrite γ-irradiated at room temperature have been investigated^1,2. The electron spin resonance spectrum, which does not decay over several months at room temperature, consists of a triplet and superimposed quintet which have been assigned to NO₂ molecules oriented in the crystal ac plane, and to N₂O₄⁻ radical-ions oriented in the bc plane, respectively. The irradiated crystals have a broad absorption band between 5250 and 4000 Å, with a maximum near the observational limit of 4000 Å, which has been assigned to NO₂ (ref. 2). Earlier electron spin resonance work, in which single crystals were irradiated and examined at 77° K, indicated the formation of NO₂ molecules oriented in the bc plane³. The electron spin resonance spectrum is slowly annealed out, without any change of hyperfine splitting or appearance of new radicals, as crystals are gradually warmed to room temperature^2,3. In order to gain a better understanding of the different behaviour at the two temperatures we have re-examined the radiolysis at room temperature, and measured the relative rates of formation of the two paramagnetic species. In the following it is assumed that the assignments of the spectra as already summarized here are correct.