EPR measurements of the time dependence of color centers in potassium azide

Abstract

Measurements have been made of the amplitudes of EPR signals for $\mathrm{N}_{2}^{\ensuremath{-}}$, N${\mathrm{O}}_{2}$, N$\mathrm{O}_{2}^{2\ensuremath{-}}$, and alternate N$\mathrm{O}_{2}^{2\ensuremath{-}}$ color centers in K${\mathrm{N}}_{3}$ as these color centers develop under irradiation with ultraviolet light. It is found that the buildups of N${\mathrm{O}}_{2}$, N$\mathrm{O}_{2}^{2\ensuremath{-}}$, and $\mathrm{N}_{2}^{\ensuremath{-}}$ all occur slowly at first, then increase at a rapid rate, and finally approach saturation. Further, they all build at similar rates. The alternate N$\mathrm{O}_{2}^{2\ensuremath{-}}$, however, has a different form and buildup rate. Based on the assumption that two excited azide ions interact with nitrate or nitrite impurities, equations have been developed which appear to adequately describe the buildup of N${\mathrm{O}}_{2}$, N$\mathrm{O}_{2}^{2\ensuremath{-}}$, and $\mathrm{N}_{2}^{\ensuremath{-}}$ color centers, thus indicating that the creation of ${\mathrm{N}}_{2}^{\ensuremath{-}}$ depends on the presence of electron traps and that nitrate and nitrite impurities may provide the needed traps.