A detailed state-to-state low-energy dynamics study of the reaction O(3<i>P</i>)+OH(2Π)→O2(<i>X</i> 3Σ<i>g</i>−)+H(2<i>S</i>) using a quasiclassical trajectory–internal-energy quantum-mechanical-threshold method

Abstract

The quasiclassical trajectory (QCT) method has been used for a detailed study of the state-to-state dynamics of the reaction O(3P) + OH(2Π)→O2(X̂33Σ−g) + H(2S) over the range of translational energies 0.125 ≤ Etr/kcal mol−1≤2.0, corresponding to the temperature range 40≤T/K≤680. A novel variant of this method insuring that trajectory calculations properly account for the zero-point energy of the diatomic molecules, the so-called quasiclassical trajectory–internal-energy quantum-mechanical-threshold method, is also suggested and applied to the title reaction. The most recent and accurate double many-body expansion potential-energy surface for the ground doublet state of the hydroperoxyl radical has been employed in all calculations. The computed reactive cross sections for initial quantum rotational states of OH varying from J=0 to J=10 (the vibrational quantum number is kept fixed at v=0) are shown to have a marked decreasing dependence on translational energy, thus suggesting that long-range forces play a major role on the dynamics of the O(3P) + OH(2Π) reaction. A comparison of the thermalized rate coefficients with the results of direct experimental measurements is shown to agree best with the data of Howard and Smith over the whole range of temperatures covered by experiment. It is also shown that nonstatistical recrossing effects are important for all translational energies and rotational states, while a nearly linear dependence is shown over the range of translational energies that have been studied. Finally, appropriate averaging over the initial conditions shows that the dependence on temperature of the calculated recrossing factor is in good agreement with the corresponding estimate from recent direct thermalized QCT calculations using the same potential-energy surface while fitting well by a recently proposed model for this recrossing factor.