Solid state and solution nitrate photochemistry: photochemical evolution of the solid state lattice.

We examined the deep UV 229 nm photochemistry of NaNO3 in solution and in the solid state. In aqueous solution excitation within the deep UV NO3¯ strong π → π* transition causes the photochemical reaction NO3¯ → NO2¯ + O·. We used UV resonance Raman spectroscopy to examine the photon dose dependence of the NO2¯ band intensities and measure a photochemical quantum yield of 0.04 at pH 6.5. We also examined the response of solid NaNO3 samples to 229 nm excitation and also observe formation of NO2¯. The quantum yield is much smaller at ∼10−8. The solid state NaNO3 photochemistry phenomena appear complex by showing a significant dependence on the UV excitation flux and dose. At low flux/dose conditions NO2¯ resonance Raman bands appear, accompanied by perturbed NO3¯ bands, indicating stress in the NaNO3 lattice. Higher flux/dose conditions show less lattice perturbation but SEM shows surface eruptions that alleviate the stress induced by the photochemistry. Higher flux/dose measurements cause cratering and des...