화학공학소재연구정보센터
Journal of Physical Chemistry A, Vol.115, No.31, 8616-8622, 2011
Kinetics of the Self Reaction of Cyclohexyl Radicals
The kinetics of the self-reaction of cyclohexyl radicals was studied by laser photolysis/photoionization mass spectroscopy. Overall rate constants were obtained in direct real-time experiments in the temperature region 303 520 K and at bath as (helium with up to 5% of radical precursors) densities (3.00-12.0) x 10(18) molecules cm(-3). Cyclohexyl radicals were produced by a combination of the 193 nm photolysis of oxalyl chloride ((CClO)(2)) with the subsequent fast reaction of Cl atoms with cyclohexane, and their initial concentrations were determined from real-time profiles of HCl. The observed overall c-C(6)H(11) + c-C(6)H(11) rate constants demonstrate negative temperature dependence, which can be described by the following expressions: k(1) = 4.8 x 10(-12) exp(+542 K/T) cm(3) molecule(-1) s(-1) with estimated uncertainty of 16% over the 303-520 K temperature range. The fraction of disproportionation equal to 41 +/- 7% was determined at 305 K; analysis of earlier experimental determinations of the disproportionation-to-recombination branching ratio leads to recommending this room-temperature value for other temperatures. The corresponding temperature dependences of the recombination (la, bicyclohexyl product) and the disproportionation (1b, cyclohexene and cyclohexane products) channels are k(1a) = 2.8 x 10(-12) exp(+542 K/T) and k(1b) = 2.0 x 10(-12) exp(+542 K/T) cm(3) molecule(-1) s(-1), with estimated uncertainties of 20% and 29%, respectively.