Kinetic Investigations of the CH (X²Π) Radical Reaction with Cyclopentadiene

Abstract

The reaction of the ground state methylidyne radical (CH (X 2 Π)) with cyclopentadiene (C 5 H 6 ) is studied in a quasi-static reaction cell at pressures ranging from 2.7 to 9.7 Torr and temperatures ranging from 298 to 450 K. The CH radical is generated in the reaction cell by pulsed-laser photolysis (PLP) of gaseous bromoform at 266 nm, and its concentration monitored using laser-induced fluorescence (LIF) with an excitation wavelength of 430.8 nm. The reaction rate coefficient is measured to be 2.70(±1.34) × 10 −10 cm 3 molecule −1 s −1 at room temperature and 5.3 Torr and found to be independent of pressure or temperature over the studied experimental ranges. DFT and CBS-QB3 methods are used to calculate the reaction potential energy surface (PES) and to provide insight into the entrance channel of the reaction. The combination of the experimentally determined rate constants and computed PES supports a fast, barrierless entrance channel that is characteristic of CH radical reactions and could potentially lead to the formation of benzene isomers.

A bonding evolution theory study of the reaction between methylidyne radical, CH(X2Π), and cyclopentadiene, C5H6

“…The mechanism is depicted in Scheme 1, with the C atoms numbering and the relative energies of the stationary points in parenthesis (kJ mol À1 ). The names of the species participating in the mechanism are taken from the Caster work [14].…”

“…An analysis of the energy values showed that all pathways were found to be strongly exothermic, and all the stationary points found lied well below the energy of the reactants [14]. From the TSs geometries, we have now conducted the IRC calculations.…”

“…The geometry optimizations of the stationary points were performed by Caster et al [14] using the Gaussian 09 program [15]. At the unrestricted B3LYP/CBSB7 level that selects the 6-311G(2d,d,p) basis set used by CBS-QB3 high accuracy energy method.…”

PAH Growth in Flames and Space: Formation of the Phenalenyl Radical

“…Additionally, expansion of a five-membered ring to a six-membered ring has been demonstrated through the reaction of pyrrole with the methylidyne radical (CH) to form pyridine 50 , and the reaction of cyclopentadiene with CH to form benzene (Figure 1c) 51,52 . CH in its ground state has been detected in combustion environments [53][54][55] , the interstellar medium 56,57 and under plasma conditions 58 .…”

“…CH in its ground state has been detected in combustion environments [53][54][55] , the interstellar medium 56,57 and under plasma conditions 58 . Reactions between CH and small unsaturated hydrocarbons and carbonyls can result in CH insertion to a π-bond through a cyclic intermediate (cycloaddition) followed by ring-opening 51,[59][60][61][62] . This reaction has a negligible activation barrier, resulting in fast reaction rates.…”