Investigation of ethynyl radical kinetics using infrared diode laser kinetic spectroscopy

[摘要] High resolution infrared diode laser kinetic spectroscopy has been used to investigate the properties of C$sb2$H reaction kinetics. The ethynyl radical (C$sb2$H) was produced in a flowing system by excimer laser photolysis (ArF, 193 nm) of either CF$sb3$CCH or C$sb2$H$sb2$ and the transient infrared absorptions of C$sb2$H or possible reaction products were followed with the diode laser probe. The kinetics of the C$sb2$H + O$sb2$ reaction were studied with a goal of determining the reaction products. Only two reaction products were observed, CO and CO$sb2$, with the amount of CO produced being about five times larger than the amount of CO$sb2$ produced. Both products are produced in vibrationally excited states. CO$sb2$ was produced long after C$sb2$H reacted and thus is not a product of the direct reaction. Two processes leading to CO formation have been observed: a fast, direct process for which the rate of CO appearance approximately matches the rate of C$sb2$H decay and a much slower indirect process. The fast process produces vibrationally excited CO (v = 5 $gets$ 4 and higher). The indirect process is observed to be dominant for the lower vibrational transitions and its rate exhibits saturation with increasing O$sb2$ pressure. In order to approximate these kinetics, it appears that at least two intermediates between C$sb2$H and CO must be involved for the indirect process. In other kinetic studies, the rate constants of C$sb2$H reactions were measured to see if other C$sb2$H reactions might exhibit addition channels. The time decay of a C$sb2$H infrared absorption line originating from the ground vibronic state was monitored as a function of reactant pressure to determine a second order rate constant. When possible the dependence of the reaction rate on helium pressure was investigated over the range of 8-70 Torr. Second order rate constants of 3.0(2) $imes$ 10$sp{-12}$, 1.3(3) $imes$ 10$sp{-10}$, 3.6(2) $imes$ 10$sp{-11}$, 4.4(4) $imes$ 10$sp{-13}$, 2.3(3) $imes$ 10$sp{-13}$ cm$sp3$ molecule$sp{-1}$ s$sp{-1}$ were obtained for the reactions of C$sb2$H with CH$sb4$, C$sb2$H$sb4$, C$sb2$H$sb6$, H$sb2$ and D$sb2$ respectively. A third order rate constant of 2.1(3) $imes$ 10$sp{-30}$ cm$sp6$ molecule$sp{-2}$ s$sp{-1}$ was obtained for the reaction of C$sb2$H with CO.

[发布机构] Rice University