Exploring the Reactivity of the CH Radical toward Nitrous Oxide in the Context of the Interstellar Medium

Experimental measurements of the kinetics of the CH + N₂O reaction are reported for the first time for the temperature range of 32(3) - 110(4) K using the recently commissioned highly instrumented low temperature reaction chamber (HILTRAC). Furthermore, we report the characterization of a new Laval nozzle to achieve uniform supersonic flow (USF) temperatures of 73(3), 86(4), and 110(4) K with an argon buffer gas. CH radicals generated from photolysis of CHBr₃ at 248 nm were detected by laser-induced fluorescence using the CH B ²Σ^- ← X ²Π (1,0) Q₂(1) transition near 364 nm, measuring the pseudo-first-order rate coefficients in the presence of N₂O. From these experiments, the reaction rate coefficient at 32(3) K was measured to be 1.7(1) × 10^-10 cm³ molecule^-1 s^-1 and is at least a factor of 2 greater than the previously measured value at room temperature. The reaction rate coefficient was found to exhibit a positive temperature-dependence below 50 K, while exhibiting a negative temperature-dependence at higher temperatures. We also report the reaction potential energy surface for this reaction, performing ab initio calculations at the CCSD(T)/aug-cc-pV(Q+d)Z//M06-2X-D3/aug-cc-pV(Q+d)Z level of theory. From this, we identified reaction pathways leading to exothermic product channels for NO + HCN, NO + HNC, N₂ + HCO, and N₂ + H + CO, suggesting that NO + HCN are the primary reaction products due to the barrierless nature of this reaction pathway. Finally, a modified Arrhenius fit to all experimental data (32-1300 K) yields k(T) = (9.3(4) × 10^-11) × (T/300)^-1.03(6) exp(-52(5)/T) cm³ molecule^-1 s^-1, which can be incorporated into astrochemical models to better understand the nitrogen-based chemistry of the interstellar medium.