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.
| Identifer | oai:union.ndltd.org:RICE/oai:scholarship.rice.edu:1911/16361 |
| Date | January 1990 |
| Creators | Lander, Deborah Rosemary |
| Contributors | Curl, R. F. |
| Source Sets | Rice University |
| Language | English |
| Detected Language | English |
| Type | Thesis, Text |
| Format | 121 p., application/pdf |
Page generated in 0.0081 seconds