Quantum reactive scattering calculations of cross sections and rate constants for the N(2D) + O2(X3Σg-) → O(3Π) + NO(X2Π) reaction

Abstract

Time-dependent quantum wavepacket calculations have been performed on the two lowest adiabatic potential energy surfaces (2 2A´ and 1 2A˝) for the N(2D) + O2(X3Σg-) → O(3Π) + NO(X2Π) reaction. The calculations have been carried out, on these recently published potential energy surfaces, using the real wavepacket method together with a new dispersion fitted finite difference technique for evaluating the action of the radial kinetic energy operator. Reaction probabilities, corresponding to the O2 reactant in its ground vibrational-rotational state, have been calculated for both surfaces and for many different values of the total angular momentum quantum number (J), within the helicity decoupling approximation. The reaction probabilities associated with all other relevant J values have been interpolated, and to a smaller extent extrapolated, using a capture model, to yield probabilities as a function of energy. The probabilities have in turn been summed to yield energy dependent cross sections and then used to compute rate constants. These rate constants are compared with ones obtained from quasiclassical trajectory (QCT) and variational transition state theory (VTST) calculations performed on the same surfaces. There is a good agreement between the wavepacket and QCT cross sections for reaction on both potential energy surfaces considered, with the exception of the near threshold region, where the reaction probability is dominated by tunnelling. Comparison of the predicted rate constants shows that for the 2 2A´ surface, above 300 K, the wavepacket, QCT and VTST results are quite similar. For the 1 2A˝ surface, however, significant differences occur between the wavepacket and the other methods. These differences become smaller with increasing temperature. It is likely that these differences arise, at least in part, from the fact that, when calculating the rate constants, the reactants are restricted to be in their lowest vibrational-rotational state in the wavepacket calculations but are selected from a thermally equilibrated population in the other methods.