Asymptotic potentials and rate constants in the adiabatic capture centrifugal sudden approximation for X+OH(X2Π)→OX+H(2S) reactions where X=O(3P), S(3P) or N(4S)

Statistical theory for the reaction N + OH → NO + H: thermal low-temperature rate constants

The reaction N + OH → NO + H involves the intermediate formation of NOH adducts which in part rearrange to HNO conformers. A statistical treatment of the process is developed in which an initial adiabatic channel capture of the reactants is accompanied by partial primary redissociation of the N⋯OH collision pairs. A criterion for the extent of this primary redissociation in competition to the formation of randomized, long-lived, complex of NOH is proposed. The NOH adducts then may decompose to NO + H, rearrange in a unimolecular process to HNO, or undergo secondary redissociation back to the reactants N + OH, while HNO may also decompose to NO + H. As the reactants N(⁴S) + OH(²Π) have open electronic shells, non-Born-Oppenheimer effects have to be considered. Their influence on thermal rate constants of the reaction at low temperatures is illustrated and compared with such effects in other reactions such as C(³P) + OH(²Π).

Quantum dynamics study on the CHIPR potential energy surface for the hydroperoxyl radical: the reactions O + OH⇋O2 + H

Quantum scattering calculations of the O((3)P)+OH((2)Π)⇌O2((3)Σg (-))+H((2)S) reactions are presented using the combined-hyperbolic-inverse-power-representation potential energy surface [A. J. C. Varandas, J. Chem. Phys. 138, 134117 (2013)], which employs a realistic, ab initio-based, description of both the valence and long-range interactions. The calculations have been performed with the ABC time-independent quantum reactive scattering computer program based on hyperspherical coordinates. The reactivity of both arrangements has been investigated, with particular attention paid to the effects of vibrational excitation. By using the J-shifting approximation, rate constants are also reported for both the title reactions.

Electronic nonadiabatic effects in low temperature radical-radical reactions. I. C(3P) + OH(2Π)

The formation of collision complexes, as a first step towards reaction, in collisions between two open-electronic shell radicals is treated within an adiabatic channel approach. Adiabatic channel potentials are constructed on the basis of asymptotic electrostatic, induction, dispersion, and exchange interactions, accounting for spin-orbit coupling within the multitude of electronic states arising from the separated reactants. Suitable coupling schemes (such as rotational + electronic) are designed to secure maximum adiabaticity of the channels. The reaction between C((3)P) and OH((2)Π) is treated as a representative example. The results show that the low temperature association rate coefficients in general cannot be represented by results obtained with a single (generally the lowest) potential energy surface of the adduct, asymptotically reaching the lowest fine-structure states of the reactants, and a factor accounting for the thermal population of the latter states. Instead, the influence of non-Born-Oppenheimer couplings within the multitude of electronic states arising during the encounter markedly increases the capture rates. This effect extends up to temperatures of several hundred K.

A global ab initio potential energy surface for the X2A' ground state of the Si + OH → SiO + H reaction

We report the first global potential energy surface (PES) for the X(2)A' ground electronic state of the Si((3)P) + OH(X(2)Π) → SiO(X(1)Σg(+)) + H((2)S) reaction. The PES is based on a large number of ab initio energies obtained from multireference configuration interaction calculations plus Davidson correction (MRCI+Q) using basis sets of quadruple zeta quality. Corrections were applied to the ab initio energies in the reactant channel allowing a proper description of long-range interactions between Si((3)P) and OH(X(2)Π). An analytical representation of the global PES has been developed by means of the reproducing kernel Hilbert space method. The reaction is found barrierless. Two minima, corresponding to the SiOH and HSiO isomers, and six saddle points, among which the isomerization transition state, have been characterized on the PES. The vibrational spectra of the SiOH/HSiO radicals have been computed from second-order perturbation theory and quantum dynamics methods. The structural, energetic, and spectroscopic properties of the two isomers are in good agreement with experimental data and previous high quality calculations.