Pulse Radiolysis of NO : Production of NO2 and N2O3 and the Production and Relaxation of Vibrationally Excited NO

Radiolysis of NO with a 30‐nsec pulse of 2‐MV electrons produces absorption bands attributed to NO₂, N₂O₃, and vibrationally excited NO. In pure NO at 1 atm, most of the NO₂ forms during the pulse, but the formation of N₂O₃ is slower $\text{(τ\hspace{0.17em}=\hspace{0.17em}0.3 μ}\sec )$ . The NO₂ is produced by the reaction of O atoms with NO, and the pseudo‐first‐order rate constant for formation of NO₂ in an 11% NO–Ar mixture is slightly lower than that calculated from published values. The N₂O₃ comes from the equilibrium NO₂ + NO⇆N₂O₃, which is achieved in <1 μsec, orders of magnitude faster than the previously estimated lower limit. The sum of yields of the two products (10.6 ± 0.5 molecules/100 eV) was independent of the pulse dose, but the ratio G(NO₂) / G(N₂O₃) increased with dose. This can be explained by a shift in the above equilibrium caused by the temperature increase produced by the pulse. Superimposed on the broad N₂O₃ band in the ultraviolet was a sharp band at 2362 Å, indicating population of the first vibrational level of NO. The relaxation lifetime was 5.8 μsec for 13% NO in Ar and 1.6 μsec for 41% NO, giving a quenching probability by NO of 2.1 ± 0.2 × 10⁻⁴ compared with 3.6 ± 0.4 × 10⁻⁴ reported by Basco, Callear, and Norrish. A small amount of absorption in the (0, 2) band at 2472 Å decayed with a lifetime ∼1.4 μsec, giving a probability for resonant vibration–vibration exchange of only ∼10⁻³.