Kinetic studies of chlorobenzene reactions with hydrogenatoms and phenyl radicals and the thermochemistryof 1-chlorocyclohexadienyl radicals

摘要

Atomic H and Cl were monitored by time-resolved resonance spectroscopy in the vacuum ultraviolet, following 193 nm laser flash photolysis of C6H5Cl and mixtures with NH3, over 300–1020 K and with Ar bath gas pressures from 30 to 440 mbar. Below 550 K simple exponential decays of [H] were observed, and attributed to addition to form chlorocyclohexadienyl radicals. This addition was reversible over 550–630 K and the equilibrium constant was determined by a third law approach. The addition rate constant can be summarized as (1.51 ± 0.11) ×10-11exp((-1397 ± 29)/T) cm3 molecule-1 s-1 (300–630 K, 1r uncertainties), and the C–H bond dissociation enthalpy in 1-chlorocyclohexadienyl was determined to be 108.1 ± 3.3 kJ mol-1 at 298 K. At higher temperatures the photolysis of chlorobenzene yielded H atoms, which is attributed to the reaction of phenyl with chlorobenzene with a rate constant of (4.5 ± 1.8) ×10-10exp((-4694 ± 355)/T) cm3 molecule-1 s-1 over 810–1020 K. These and other reaction pathways are discussed in terms of information about the potential energy surface obtained via B3LYP/ 6-311G(2d,d,p) density functional theory.