Reaction rates and kinetic isotope effects of H2 + OH → H2O + H

Abstract

We calculated reaction rate constants including atom tunneling of the reaction of dihydrogen with the hydroxy radical down to a temperature of 50 K. Instanton theory and canonical variational theory with microcanonical optimized multidimensional tunneling (CVT/µOMT) were applied using a fitted potential energy surface [J.Chem. Phys. 138, 154301 (2013)

Atom Tunneling in the Water Formation Reaction H2 + OH → H2O + H on an Ice Surface

“…[112][113][114][115] The inverse KIE for the deuteration of OH was also present in the gas-phase reaction rate constants where the difference in zero-point energy corrected activation barrier between the HHOH and the HHOD system is 1.3 kJ mol −1 (156 K). 42 In the unimolecular case, the primary KIEs are ≈ 5 at 200 K and increase to ≈ 300 at 60 K. The secondary KIEs play an even smaller role than in the bimolecular case and no inverse KIE is present, see Fig. 8.…”

“…For the bimolecular case, the KIEs are similar to the ones reported in the gas phase. 42 The secondary KIEs play a smaller role as they are in all cases smaller than 10. When substituting OH by OD, an inverse KIE is found, i.e., the rate constant increases due to deuteration.…”

“…39,41,42 Oba et al found experimental evidence that the reaction of H 2 and OH to wa-ter and hydrogen atoms also occurs on surfaces even at 10 K due to atom tunneling. 44 Recently, we published an extensive study on the reaction of molecular hydrogen and hydroxyl radicals (equation (R 9)) in the gas phase including all possible isotope patterns down to 80 K. 42 Here, we extend this work to the adsorption of OH radicals onto crystalline I h water ice and the subsequent reaction with H 2 . We present binding sites, energies, reaction paths and reaction rate constants for the reaction of H 2 with OH on the surface.…”

Rigorous close-coupling quantum dynamics calculation of thermal rate constants for the water formation reaction of H2 + OH on a high-level PES

“…56 All these approaches have been employed to study the title reaction. 57,58 It should also be noted that, while RPMD and semi-empirically corrected TST account for overall rotation, this is not true for instanton calculations, which employ the J-shifting approximation, 59 which previously has been assessed to give significant errors for the title reaction. 13 In this article, accurate full-dimensional close-coupling calculations of the thermal rate constant for the title reaction are presented.…”

Low‐Temperature Thermal Rate Constants for the Water Formation Reaction H2+OH from Rigorous Quantum Dynamics Calculations

“…This can be attributed to the large differences between the semi-empirical SE PES and the highly accurate NN1 PES.T he SE PES exhibits ahigher classical barrier,but alower zero-pointenergy-corrected barrier than the NN1 PES.The SE PES also shows ah igher barrier frequency than the NN1 PES,w hich places agreater importance on tunneling and results in atoo strong curvature of the TRC.Aswas pointed out in previous work, the fit of the SE PES to the ab initio data is not great in the transition-state region as can, for example,beseen by the large deviations of the moment of inertia and the harmonic frequencies computed at the PES and ab initio transition states. [31,32] Thef ull-dimensional TRCs on the NN1 PES are compared to experimental [67][68][69][70] as well as approximate simulations employing instanton theory [25] and RPMD [26] in Figure 2. The accurate TRCs calculated using the NN1 PES are in very good agreement with the experimental data.…”