Investigation of Product Formation in the O(1D, 3P) + N2O Reactions: Comparison of Experimental and Theoretical Kinetics

The spin-forbidden and spin-allowed reactions of the excited and ground electronic state O(¹D, ³P) + N₂O(X¹Σ⁺) systems have been studied theoretically. Quantum calculations at the UCCSD(T)/CBS(T, Q, 5)//CCSD/aug-cc-pVTZ level have located two crossing points, MSX1 and MSX2, with energies of 11.2 and 22.7 kcal mol^-1 above O(³P) + N₂O, respectively. The second-order P-independent rate constants for the adiabatic and non-adiabatic thermal reactions predicted by adiabatic TST/VTST and non-adiabatic TST, respectively, agree closely with the available literature results. The second-order rate constant, k_2a = 9.55 × 10^-11 exp(-26.09 kcal mol^-1/RT) cm³ molecule^-1 s^-1, for the O(³P) + N₂O → 2NO reaction, contributed by both the dominant MSX2 and the minor TS1-a channels, is in reasonable accord with prior experiments and recommendations, covering the temperature range of 1200-4100 K. The calculated rate constant, k_2b = 4.47 × 10^-12 exp(-12.9 kcal mol^-1/RT) cm³ molecule^-1 s^-1, for the O(³P) + N₂O → N₂ + O₂(a¹Δ_g) reaction, occurring exclusively via MSX1, is also in good agreement with the combined experimental data measured in a shock tube study at T = 1940-3340 K (ref 16) and the result measured by Fourier transform infrared spectroscopy in the temperature range of 988-1083 K (ref 17). Moreover, the spin-allowed rate constants predicted for the singlet-state reactions, k_1a = (7.06-7.46) × 10^-11 cm³ molecule^-1 s^-1 for O(¹D) + N₂O → 2NO and k_1b = (4.36-4.66) × 10^-11 cm³ molecule^-1 s^-1 for O(¹D) + N₂O → N₂ + O₂(a¹Δ_g) in the temperature range of 200-350 K, agree quantitatively with the experimentally measured data, while the total rate constant k₁ = k_1a + k_1b was also found to be in excellent accordance with many reported values.