title: Solid state and solution nitrate photochemistry: photochemical evolution of the solid state lattice.
abstract: We examined the deep UV 229 nm photochemistry of NaNO(3) in solution and in the solid state. In aqueous solution excitation within the deep UV NO(3)¯ strong π → π* transition causes the photochemical reaction NO(3)¯ → NO(2)¯ + O·. We used UV resonance Raman spectroscopy to examine the photon dose dependence of the NO(2)¯ band intensities and measure a photochemical quantum yield of 0.04 at pH 6.5. We also examined the response of solid NaNO(3) samples to 229 nm excitation and also observe formation of NO(2)¯. The quantum yield is much smaller at ∼10(-8). The solid state NaNO(3) photochemistry phenomena appear complex by showing a significant dependence on the UV excitation flux and dose. At low flux/dose conditions NO(2)¯ resonance Raman bands appear, accompanied by perturbed NO(3)¯ bands, indicating stress in the NaNO(3) 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 destruction of the NaNO(3) surface as the surface layers are converted to NO(2)¯. Modest laser excitation UV beams excavate surface layers in the solid NaNO(3) samples. At the lowest incident fluxes a pressure buildup competes with effusion to reach a steady state giving rise to perturbed NO(3)¯ bands. Increased fluxes result in pressures that cause the sample to erupt, relieving the pressure.
authors.affiliation: Department of Chemistry, University of Pittsburgh, Pittsburgh, Pennsylvania 15260, United States. asher@pitt.edu
authors.forename: Sanford A
authors.initials: SA
authors.lastname: Asher
authors.forename: David D
authors.initials: DD
authors.lastname: Tuschel
authors.forename: Todd A
authors.initials: TA
authors.lastname: Vargson
authors.forename: Luling
authors.initials: L
authors.lastname: Wang
authors.forename: Steven J
authors.initials: SJ
authors.lastname: Geib
mesh_terms: D009566:Nitrates / Q000737:chemistry*; D010777:Photochemistry; D012996:Solutions; D013059:Spectrum Analysis, Raman; D014466:Ultraviolet Rays
chemical_list: D009566:Nitrates; D012996:Solutions; C031618:sodium nitrate