The unimolecular decomposition of 1-chloroethyl radical

Abstract

The kinetics of the unimolecular decomposition of the 1-chloroethyl radical have been studied. The reaction was isolated for quantitative study in a heated tubular flow reactor coupled to a photoionization mass spectrometer. Rate constants for the decomposition were obtained in time-resolved experiments as a function of temperature (848--980 K) and bath gas density (3--22 {times} 10{sup 16} molecule/cm{sup 3}) in He, Ar, and N{sub 2}. The rate constants are in the falloff under the conditions of the experiments. The falloff behavior was analyzed using a Master Equation analysis. A transition state model was created to obtain values of the microcanonical rate constants, k(E), needed to solve the Master Equation. The transition state model provides the high-pressure limit rate constants for the decomposition reaction (k{sub 1}{sup {infinity}} (CH{sub 3}CHCl = CH{sub 2}CHCl + H) = 1.94 {times} 10{sup 9} T{sup 1.22} exp({minus}19,510 K/T)/s) and the reverse reaction (k{sub {minus}1}{sup {infinity}} (H + CH{sub 2}CHCl = CH{sub 3}CHCl + H) = 3.35 {times} 10{sup {minus}14} T{sup 0.86} exp({minus}75.3 K/T) cm{sup 3}/molecule s). Values of {l_angle}{Delta}E{r_angle}{sub down} for the energy loss probability were obtained for each experiment using the exponential-down model. The values of {l_angle}{Delta}E{r_angle}{sub down} display a pronounced positive temperature dependence withmore » average values of 255 (He), 360 (Ar), and 261 (N{sub 2}) cm{sup {minus}1}. Parameterization of the temperature and pressure dependence of the unimolecular rate constant for the temperature range 298--1,500 K and pressures 0.001--10 atmospheres is provided using the modified Lindemann-Hinshelwood expression.« less