Kinetic Studies of Nitrate Radicals: Flash Photolysis at 193 nm

Nitrate radicals, NO₃, were produced for the first time by 193 nm laser flash photolysis of N₂O₅ and HNO₃. Detection was achieved due to NO₃'s strong absorption at 622.7 nm confirmed by measurements of the absorption spectrum in the range of 617–625 nm using both NO₃ precursors. Time‐resolved kinetic studies allowed the determination of room temperature rate coefficients for the reactions of NO₃ with 2‐methylbut‐2‐ene and NO₂ of (1.28 ± 0.11) × 10^?11 and (8.4 ± 1.2) × 10^?13 cm³ molecule^?1 s^?1, respectively. The rate coefficients compare well to previous measurements with alternative techniques, suggesting that the reported method is valid and may be applied in follow‐up studies. The rate coefficient for 2‐methylbut‐2‐ene is compared to previous measurements and predictions for the alkene as well as the related alkenol. The new data are consistent with a previously suggested deactivation of the reactive site of the double bond if adjacent to an OH group. A calculated atmospheric lifetime for 2‐methylbut‐2‐ene with respect to NO₃‐initiated oxidation of less than 3 min suggests predominant removal by NO₃ in the atmosphere.