Title

Quantum Chemical Study of Trimolecular Reaction Mechanism between Nitric Oxide and Oxygen in the Gas Phase

Authors

Authors

O. B. Gadzhiev; S. K. Ignatov; A. G. Razuvaev;A. E. Masunov

Comments

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Abbreviated Journal Title

J. Phys. Chem. A

Keywords

CONSISTENT BASIS-SETS; POTENTIAL-ENERGY SURFACE; RIDGE INFLECTION; POINTS; HYBRID DENSITY FUNCTIONALS; TRANSITION-METAL DIMERS; THERMOCHEMICAL KINETICS; EQUILIBRIAL PATHS; SYMMETRY-BREAKING; NITROGEN-DIOXIDE; SINGLET OXYGEN; Chemistry, Physical; Physics, Atomic, Molecular & Chemical

Abstract

Singlet and triplet potential energy surfaces of the reaction between molecular oxygen and two nitric oxide(II) molecules were studied by quantum chemical methods (coupled cluster, CASSCF, and density functional theory: B3LYP, TPSS, VSXC, BP86, PBE, B2-PLYP, B2K-PLYP). Elementary steps involving various N(2)O(4) isomers (cyclic, cis-cis-, cis-trans-, trans- trans-ONOONO, cis- and irans-ONONO(2), O(2)NNO(2)) were considered, as well as weakly bound molecular clusters preceding formation of O(2)NNO(2), and Coupe-type quasi-aromatic hexagonal ring intermediate NO(2)center dot O(2)N. We found that activation energy strongly depends on the conformation of ONOONO peroxide, which is formed barrierlessly, The best agreements with experimental values were achieved by the B3LYP functional with aug-pc3 basis set. The lowest transition state (TS) energies correspond to the following reaction channel: 2NO + O(2) (0 KJ/mol) -> cis-cis-ONOONO (-45 kJ/mol) -> TS1 -> NO(2)center dot O(2)N (-90 kJ/mol) -> TS2 -> cis-ONONO(2) (-133 kJ/mol)-> TS3 -> trans-ONONO(2) (-144 kJ/mol) -> TS(4) -> O(2)NNO(2) (-193 kJ/mol). A valley ridge inflection (VRI) point is located on the minimum energy path (MEP) connecting NO(2)center dot O(2)N and cis-ONONO(2). The energy landscape between NO(2)center dot O(2)N and CC-TS2 can be classified as a downhill valley-pitch fork VRI bifurcation according to a recent classification of bifurcation events [Quapp, W. J. Mol. Struct. 2004, 95, 695-696]. The first and second transition states correspond to barrier heights of 10.6 and 37.0 kJ/mol, respectively. These values lead to the negative temperature dependence of the rate constant. The apparent activation enthalpy of the overall reaction was calculated to be Delta(tau)H(double dagger)(0) = -4.5 kJ/mol, in perfect agreement with the experimental value.

Journal Title

Journal of Physical Chemistry A

Volume

113

Issue/Number

32

Publication Date

1-1-2009

Document Type

Article

Language

English

First Page

9092

Last Page

9101

WOS Identifier

WOS:000268660900006

ISSN

1089-5639

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