Title: An experimental and theoretical study of the reaction of ethynyl radicals with nitrogen dioxide (HC C+NO2)
Authors: Carl, Shaun ×
Nguyen, HMT
Nguyen, Minh Tho
Peeters, Jozef #
Issue Date: Jan-2003
Publisher: Amer inst physics
Series Title: Journal of Chemical Physics vol:118 issue:24 pages:10996-11008
Abstract: A pulsed laser photolysis/chemiluminescence (PLP/CL) technique was used to determine absolute rate constants of the reaction C2H+NO2-->products over the temperature range 288-800 K at a pressure of 5 Torr (N-2). The reaction has a large rate constant that decreases with increasing temperature. It may be expressed in simple Arrhenius form as k(1)(T)=(7.6+/-1.0)x10(-11) exp[(130+/-50) K/T], although there is an indication of a downward curvature for T>700 K. A three-parameter Arrhenius fit to the data, which takes this into account gives k(1)(T)=(9.7+/-1.5)x10(-9)T(-0.68) exp[(158+/-65) K/T]. Our experiments also show that the 293 K rate constant is invariant to pressure between 2 and 11 Torr (N-2). We have also characterized the C2H+NO2 reaction theoretically. A large portion of the potential energy surface (PES) of the [C-2,H,N,O-2] system has been investigated in its electronic (singlet) ground-state using DFT with the B3LYP/6-311++G(3df,2p) method and MO computations at the CCSD(T)/6-311++G(d,p) level of theory. Seventeen isomers and thirty-two transition structures were found to connect reactants to products following eighteen different channels. Hydroxyl cyano ketone 11 and formylisocyanate 16 were found to be the most stable intermediates, although the reaction flux through them, as a fraction of the total, is likely to be small over the temperature range studied. A part of the PES corresponds with that of the HCCO+NO reaction [I. V. Tokmakov, L. V. Moskaleva, D. V. Paschenko, and M. C. Lin, J. Phys. Chem. A 167, 1066 (2003)], and the dominant product channels for C2H+NO2 proceed via the same nitrosoketene intermediate that is formed initially in the HCCO+NO reaction. However, unlike in the latter reaction, the fate of the much more highly excited nitrosoketene formed by C2H+NO2 is likely to be governed dynamically. We present arguments as to the likely product channels for C2H+NO2 based on both statistical and dynamical considerations. A statistical description overwhelmingly favors the product set HCCO+NO. Dynamical considerations on the other hand favor both the HCN+CO2 and HCCO+NO product sets. Formation of HCNO+CO appears unlikely. Energetically allowed paths, leading to five other product sets, namely, HNCO+CO, HOCN+CO, HOCC+NO, HONC+CO, and HNC+CO2, have also been identified, and are discussed. (C) 2003 American Institute of Physics.
ISSN: 0021-9606
Publication status: published
KU Leuven publication type: IT
Appears in Collections:Quantum Chemistry and Physical Chemistry Section
× corresponding author
# (joint) last author

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