Disclaimer: This material is being kept online for historical purposes. Though accurate at the time of publication, it is no longer being updated. The page may contain broken links or outdated information, and parts may not function in current web browsers. Visit https://espo.nasa.gov for information about our current projects.

 

Kinetics and Thermochemistry of the Cl(2PJ) + C2Cl4 Association Reaction

Nicovich, J. M., S. Wang, M. L. McKee, and P. Wine (1996), Kinetics and Thermochemistry of the Cl(2PJ) + C2Cl4 Association Reaction, J. Phys. Chem., 680, 680-688.
Abstract: 

A laser flash photolysis-resonance fluorescence technique has been employed to study the kinetics of the Cl(2PJ) + C2Cl4 association reaction as a function of temperature (231-390 K) and pressure (3-700 Torr) in nitrogen buffer gas. The reaction is found to be in the falloff regime between third and second order over the range of conditions investigated, although the second-order limit is approached at the highest pressures and lowest temperatures. At temperatures below 300 K, the association reaction is found to be irreversible on the experimental time scale of ∼20 ms. The kinetic data at T < 300 K have been employed to obtain falloff parameters in a convenient format for atmospheric modeling. At temperatures above 330 K, reversible addition is observed, thus allowing equilibrium constants for C2Cl5 formation and dissociation to be determined. Second- and third-law analyses of the equilibrium data lead to the following thermochemical parameters for the association reaction: ∆H°298 ) -18.1 ( 1.3 kcal mol-1, ∆H°0 ) -17.6 ( 1.3 kcal mol-1, and ∆S°298 ) -27.7 ( 3.0 cal mol-1 K-1. In conjunction with the well-known heats of formation of Cl(2PJ) and C2Cl4, the above ∆H values lead to the following heats of formation for C2Cl5 at 298 and 0 K: ∆H°f,298 ) 8.0 ( 1.3 kcal mol-1 and ∆H°f,0 ) 8.1 ( 1.5 kcal mol-1. The kinetic and thermochemical parameters reported above are compared with other reported values, and the significance of reported association rate coefficients for understanding tropospheric chlorine chemistry is discussed.

Research Program: 
Upper Atmosphere Research Program (UARP)