# Investigation of ethynyl radical kinetics using infrared diode laser kinetic spectroscopy

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 Title: Investigation of ethynyl radical kinetics using infrared diode laser kinetic spectroscopy Lander, Deborah Rosemary Curl, R. F. Doctor of Philosophy thesis 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) $\times$ 10$\sp{-12}$, 1.3(3) $\times$ 10$\sp{-10}$, 3.6(2) $\times$ 10$\sp{-11}$, 4.4(4) $\times$ 10$\sp{-13}$, 2.3(3) $\times$ 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) $\times$ 10$\sp{-30}$ cm$\sp6$ molecule$\sp{-2}$ s$\sp{-1}$ was obtained for the reaction of C$\sb2$H with CO. Lander, Deborah Rosemary. (1990) "Investigation of ethynyl radical kinetics using infrared diode laser kinetic spectroscopy." Doctoral Thesis, Rice University. http://hdl.handle.net/1911/16361. http://hdl.handle.net/1911/16361 1990