Radiation mechanisms. Part 5.—Nitrite and nitrate ions in aqueous glasses

Abstract

Acidic, neutral and alkaline aqueous glasses containing various metal nitrites or nitrates have been exposed to ⁶⁰Co γ-rays at 77 K and their e.s.r. spectra recorded over a range of temperatures. In alkaline glasses, nitrite gave NO₂ and NO^2–₂ at 77 K, but NO^2–₃ was clearly distinguished when trapped O^– was lost (NO^–₂+ O^–→ NO^2–₃). Nitrate gave only NO^2–₃ under these conditions. In neutral glasses, nitrite again gave NO₂ and NO^2–₂, but the latter was readily converted to HNO^–₂. No NO^2–₃ was formed on annealing. Nitrate in neutral glasses gave NO^2–₃ and NO₂ in relative concentrations that varied with the cation. The NO₂ radical signal was lost reversibly on slight warming above 77 K, which suggests that these radicals are only weakly associated with solvent. Two species with small hyperfine coupling to ¹⁴N (≈3 G) were detected in amounts that were again cation dependent. One was clearly NO₃(which did not rotate on slight annealing) but the other, species A, having g₁= 2.008, g₂= 2.006, g₃= 2.000, A₁= 3.3 G, A₂= 3.15 G and A₃= 1.6 G, was not identifiable with any known nitrogen radical. Species A was never formed in acidic glasses. We tentatively suggest NO^2–₄ as a possible formulation (OH + NO^–₃→ NO^2–₄+(H⁺)).

Acidic glasses containing nitrate gave only NO₂ and NO₃. The effect of added methanol was studied and it is concluded that NO₂ is formed from NO^2–₃ and not via NO₃ as has been previously supposed.