Kinetic study of the reactions of cyanyl radical with oxygen and carbon dioxide from 292 to 1500 K using high-temperature photochemistry

Abstract

Absolute rate constants for the reaction of CN with O{sub 2} have been measured as a function of temperature (292-1,565 K) and pressure (5-80 Torr), by combining the laser-induced fluorescence detection technique with high-temperature reactor technology. CN radicals were generated by using 193-nm excimer laser photolysis of dilute C{sub 2}N{sub 2}/Ar mixtures. Decays of the radical concentration were monitored by using laser-induced fluorescence (LIF) near 387 nm under pseudo-first-order conditions. The reaction of CN with O{sub 2} has a negative temperature dependence and is independent of pressure. These data contain minimal curvature and are adequately fit by the expression k ({plus minus}2{sigma}) = (1.02 {plus minus} 0.12) {times} 10{sup {minus}11} exp((+220 {plus minus} 25)/T) cm{sup 3}/(molecule s). This result represents the widest continuous temperature range over which this rate constant has been measured to date. For the reaction with CO{sub 2}, the Cn decays are complex and are strongly dependent on the gas temperature. No detectable reaction is observed for temperatures below 900 K. For temperatures above about 1150 K, CN decays are biexponential. Because of the complexities in the behavior of the data, no reliable Arrhenius rate parameters were determined.