ISSN:
1089-7690
Source:
AIP Digital Archive
Topics:
Physics
,
Chemistry and Pharmacology
Notes:
In this work, a pulsed laser photolysis/chemiluminescence (PLP/CL) technique was used to measure absolute rate coefficients for the reaction of C2H+H2→products over the temperature range 295–666 K. Ethynyl radicals were produced pulsewise by excimer laser photolysis of acetylene at 193 nm and real-time pseudo-first-order decays of C2H were monitored by the CH(A 2Δ→X 2Π) chemiluminescence resulting from their reaction with O2. Over the experimental temperature range, the results indicate that the rate coefficient exhibits a non-Arrhenius behavior in line with theoretical predictions, khydrogen(T)=3.92×10−19 T2.57±0.30 exp[−(130±140) K/T] cm3 molecule−1 s−1. Experiments were supplemented by ab initio molecular orbital calculations up to the coupled-cluster theory including all single and double excitations plus perturbative corrections for the triples, UCCSD(T), with the 6-311++G(d,p) basis set for geometry optimizations and the aug-cc-pVTZ for electronic energy single points, revealing that the direct hydrogen abstraction yielding HC(Triple Bond)CH+H is the only product channel of any importance. There is also no important crossing between the doublet and quartet energy surfaces. Finally, geometry optimizations at the UCCSD(T)/6-311++G(2df,2p) level have shown that the transition structure for H-abstraction is linear; harmonic vibration frequencies at this level, and single-point UCCSD(T)/aug-cc-pVTZ energies for these geometries result in an adiabatic barrier height for H-abstraction, including harmonic vibration zero point energies, of 12.8 kJ/mol, while the classical potential energy barrier is 9.2 kJ/mol. © 2002 American Institute of Physics.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1063/1.1436481
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