On the statistical behavior of the O+OH→H+O2 reaction: A comparison between quasiclassical trajectory, quantum scattering, and statistical calculations

Abstract

The dynamics of the O + OH reaction on the ground state potential energy surface (PES) is investigated by means of the quasiclassical trajectory method and two statistical methods: phase space theory and statistical quantum method. Preliminary calculations with an exact quantum method are also reported. The quasiclassical trajectory calculations show evidence for a phase space bottleneck inhibiting the intramolecular energy transfer between the O-H and O-O bonds. As a result, the probability of the intermediate complex dissociating back toward the reactants is high, thereby yielding a reaction probability significantly lower than expected for a barrierless and exothermic reaction. The features of the PES, which are the cause of this dynamical effect, are identified. This is essentially the conservation of the equilibrium distance of the O-H bond, hardly changed by a close encounter with an oxygen atom. The statistical calculations, which do not take into account the PES in the complex region, yield a high reaction probability, much larger than the probability calculated from the dynamical methods, both classical and quantum. If the statistical cross sections are corrected by a scaling factor, which corresponds actually to scaling the capture probability, then a good agreement is observed between dynamical and statistical calculations of the product state distributions. The differential cross sections calculated with all the methods show a backward-forward symmetry, with sharp polarization peaks. The complex lifetime is divided into two parts by the bottleneck. During the first part, the system remains trapped in a small region of the phase space and has a high probability to dissociate back toward the reactants. This is a nonstatistical effect due to the PES shape. During the second part, fast intramolecular vibrational energy redistribution takes place, leading to a statistical distribution of energy on the rovibrational states of the products. These findings indicate that the O + OH reaction has mixed dynamics, both with statistical and nonstatistical aspects.

Dynamics of the D+ + H2 → HD + H+ reaction at the low energy regime by means of a statistical quantum method

“…52, 32, and 33 for original reports, respectively, on these two techniques). These two approaches have been applied in common for a better understanding of the dynamics of several atomdiatom reactions such as N+H 2 , 53 O+OH, 54 H + +H 2 , 4,55,56 and H + +D 2 . 14,31 Numerical details of the TIQM calculation performed by Honvault and Scribano were given before.…”

Oxygen depletion in dense molecular clouds: a clue to a low O2abundance?

“…The study of this reaction has attracted considerable experimental attention (Howard & Smith 1980, 1981Lewis & Watson 1980;Brune et al 1983;Smith & Stewart 1994;Robertson & Smith 2002Carty et al 2006), and there have also been a large number of theoretical studies using a variety of methods (Harding et al 2000;Troe & Ushakov 2001;Xu et al 2007;Lin et al 2008;Lique et al 2009;Quéméner et al 2009;Maergoiz et al 2004;Jorfi et al 2009;Li et al 2010). The experimental rate constant is well determined between 140 and 300 K decreasing from 7 × 10 −11 cm 3 molecule −1 s −1 at 140 K to 3 × 10 −11 cm 3 molecule −1 s −1 at 300 K. Between 40 and 140 K, the reaction has been studied in a CRESU (Cinétique de Réaction en Ecoulement Supersonique Uniforme) apparatus (Carty et al 2006) leading to a value of around 3.5(±1.0) × 10 −11 cm 3 molecule −1 s −1 which however has large uncertainties.…”

An accurate study of the dynamics of the C+OH reaction on the second excited 14A″ potential energy surface

“…The astrophysical interest of reactions between free radicals has motivated an ample list of recent studies of collisions between open-shell atoms such as C( 3 P), [1][2][3][4][5][6][7] N( 4 S), [8][9][10] F( 2 P), [11][12][13][14] O( 3 P), [15][16][17][18] or S( 3 P) (Refs. 19 and 20) with the hydroxyl radical OH( 2 ).…”