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Article

Ab Initio and RRKM Study of the Reaction of ClO with HOCO Radicals

Supporting Info

Hua-Gen Yu^† and Joseph S. Francisco*^‡

Department of Chemistry, Brookhaven National Laboratory, Upton, New York 11973 and Department of Chemistry, Purdue University, West Lafayette, Indiana 47907

J. Phys. Chem. A, 2009, 113 (46), pp 12932–12941

DOI: 10.1021/jp9040088

Publication Date (Web): October 15, 2009

* To whom correspondence should be addressed. E-mail: francisc@purdue.edu., †

Brookhaven National Laboratory.

, ‡

Purdue University.

Abstract

The reaction pathways for the ClO + HOCO reaction have been explored using the coupled-cluster method to locate and optimize the critical points on the ground-state potential-energy surface. Results show that the ClO + HOCO reaction can produce Cl + HOC(O)O, HOCl + CO₂, HCl + CO₃, and HClO + CO₂ via an addition or a direct hydrogen abstraction reaction mechanism. The reaction kinetics has been studied using the variational RRKM theory. It is found that the ClO + HOCO reaction is fast and has a negative temperature dependence at low temperatures. At room temperature, the thermal rate coefficient is obtained as 4.26 × 10⁻¹² cm³ molecules⁻¹ s⁻¹ with product branching fractions of Cl (0.518), HOCl (0.469), HCl (0.01), and HClO (0.003) at zero pressure. The Cl + HOC(O)O products are major, compared to the HOCl + CO₂ products, because of the loose transition state along the dissociation pathway to eliminate Cl. In addition, the RRKM/master equation simulations indicate that the stabilization of the HOC(O)OCl intermediates is noticeable at moderate pressures as its thermal rate constants reach about 6.0 × 10⁻¹³ cm³ molecules⁻¹ s⁻¹. In contrast, the other product branching ratios for the ClO + HOCO reaction are weakly dependent on pressure.