No abstract

A global single-sheeted double many-body expansion potential energy surface is reported for the ground electronic state of ClO2. The potential energy surface is obtained by fitting 3200 energy points that map all atom-diatom dissociation channels as well as all relevant stationary points, including the well-known OClO and ClOO structures. The ab initio calculations are obtained at the multireference configuration interaction level of theory, employing the cc-pVXZ (X = D, T) Dunning basis sets, and then extrapolated to the complete basis set limit with the generalized uniform singlet- and triplet-pair protocol. The topographical features of the novel global potential energy surface are examined in detail.

The ClO 3 many-body expansion potential energy surface of Farantos and Murrell (Int J Quantum Chem 1978, 14, 659) has been modified along the minimum energy path for the reaction O + OClO → ClO + O 2 such as to conform with the available kinetics data. The dynamics of the title reaction is also studied for temperatures of relevance in stratospheric chemistry. Two mechanisms for ClO + O 2 formation are identified: (i) direct abstraction of a terminal oxygen atom from the OClO reactant and (ii) formation of an intermediate ClO 3 complex followed by dissociation. The novel potential energy surface gives also a good description of the kinetics of the reaction Cl + O 3 → ClO + O 2 .

Classical trajectories have been integrated to study the O + ClO reaction, both reactive and vibrational energy transfer processes, for the range of temperatures 100 ≤ T/K ≤ 500 using momentum Gaussian binning. The employed potential energy surface is the recently proposed single-sheeted double many-body expansion potential energy surface for the (2)A" ground-state of ClO2 based on multireference ab initio data. A capture-type regime with a room-temperature rate constant of (17.8 ± 0.5) × 10(-12) cm(3) s(-1) and temperature dependence of k(T/K)/cm(3) s(-1) = 22.4 × 10(-12) × T(-0.81) exp(-39.2/T) has been found. Although the value reported here is half of the experimental and recommended one, tentative explanations are given. Other dynamical attributes are also examined for the title reaction, with state-to-all and state-to-state vibrational relaxation and excitation rate constants reported for temperatures of relevance in stratospheric chemistry.