Quantum dynamics of the O+OH→H+O2 reaction at low temperatures

Abstract

We report quantum dynamics calculations of the O + OH --> H + O(2) reaction on two different representations of the electronic ground state potential energy surface (PES) using a time-independent quantum formalism based on hyperspherical coordinates. Calculations show that several excited vibrational levels of the product O(2) molecule are populated in the reaction. Rate coefficients evaluated using both PESs were found to be very sensitive to the energy resolution of the reaction probability, especially at temperatures lower than 100 K. It is found that the rate coefficient remains largely constant in the temperature range of 10-39 K, in agreement with the conclusions of a recent experimental study [Carty et al., J. Phys. Chem. A 110, 3101 (2006)]. This is in contrast with the time-independent quantum calculations of Xu et al. [J. Chem. Phys. 127, 024304 (2007)] which, using the same PES, predicted nearly two orders of magnitude drop in the rate coefficient value from 39 to 10 K. Implications of our findings to oxygen chemistry in the interstellar medium are discussed.

HERSCHELMEASUREMENTS OF MOLECULAR OXYGEN IN ORION

“…This opened the possibility that the O 2 abundance in cooler clouds would be much lower than predicted by the above astrochemical models. However, more elaborate quantum mechanical calculations by Quémener et al (2008) showed a relatively weak temperature dependence, and a rate coefficient at 10 K that is 70 times larger than predicted by Xu et al (2007).…”

Geometric phase effects in the ultracold D + HD $ \rightarrow $ D + HD and D + HD $\leftrightarrow $ H + D2reactions

“…In the ultracold regime, a single partial wave (i.e., the l=0 angular momentum partial wave or s-wave for bosons and distinguishable particles, and l=1 or p-wave for identical fermions) contributes to the scattering cross sections and the ultracold reaction rate coefficients obey the well known Bethe-Wigner threshold laws [74][75][76][77][78]. For exoergic processes these rate coefficients approach finite measurable values comparable to or even larger than their values at thermal energies [64][65][66][67][68][79][80][81][82][83]. The tiny kinetic energy associated with ultracold collisions makes them amenable to control via external electric or magnetic fields [69][70][71][72][84][85][86][87].…”

Accurate combined-hyperbolic-inverse-power-representation of ab initio potential energy surface for the hydroperoxyl radical and dynamics study of $\bf O+OH$O+OH reaction

“…Although DMBE IV is likely the most widely used due to being remarkably adequate 42 for calculating reaction rate constants, a spline interpolant to nearly 18 000 ab initio points 43 calculated at the internally contracted multireference configuration interaction 44 level with the Davidson correction and an augmented quadruplezeta correlation consistent basis set [45][46][47] (MRCI+Q/AVQZ) has emerged. Many theoretical investigations 40,42,[48][49][50][51][52][53][54] of the O + OH rate constant below 50 K have utilized the latter, hereinafter named XXZLG, 55 or both this and DMBE IV. Experimentally, the O + OH reaction has also been much studied, [56][57][58] and rate constants recommended.…”