Kinetics of the reactions of C₂H₅, n‐C₃H₇, and n‐C₄H₉ radicals with Cl₂ at the temperature range 190–360 K

Abstract

The kinetics of the C 2 H 5 + Cl 2 , n-C 3 H 7 + Cl 2 , and n-C 4 H 9 + Cl 2 reactions has been studied at temperatures between 190 and 360 K using laser photolysis/photoionization mass spectrometry. Decays of radical concentrations have been monitored in time-resolved measurements to obtain reaction rate coefficients under pseudo-first-order conditions. The bimolecular rate coefficients of all three reactions are independent of the helium bath gas pressure within the experimental range (0.5-5 Torr) and are found to depend on the temperature as follows (ranges are given in parenthesis): k(C 2 H 5 + Cl 2 ) = (1.45 ± 0.04) × 10 −11 (T /300 K) −1.73 ± 0.09 cm 3 molecule −1 s −1 (190-359 K), k(n-C 3 H 7 + Cl 2 ) = (1.88 ± 0.06) × 10 −11 (T /300 K) −1.57 ± 0.14 cm 3 molecule −1 s −1 (204-363 K), and k(n-C 4 H 9 + Cl 2 ) = (2.21 ± 0.07) × 10 −11 (T /300 K) −2.38 ± 0.14 cm 3 molecule −1 s −1 (202-359 K), with the uncertainties given as one-standard deviations. Estimated overall uncertainties in the measured bimolecular reaction rate coefficients are ±20%. Current results are generally in good agreement with previous experiments. However, one former measurement for the bimolecular rate coefficient of C 2 H 5 + Cl 2 reaction, derived at 298 K using the very low pressure reactor method, is significantly lower than obtained in this work

An Experimental Study of the Kinetics of the Reactions of Isopropyl,sec-Butyl, andtert-Butyl Radicals with Molecular Chlorine at Low Pressures (0.5-7.0 Torr) in the Temperature Range 190-480 K

“…They also observed a much weaker temperature dependence. A similar observation was made in our previous work when we compared our results with the results of Timonen and Gutman . This is somewhat surprising, given how similar the two experimental setups are.…”

“…We rationalize this from the fact that in a previous R ● + NO 2 kinetic study, we used both precursors (2‐bromopropane and 2‐nitropropane) to produce isopropyl radicals and observed consistent results . In CH 3 + Cl 2 and C 2 H 5 + Cl 2 reactions , which have been studied before with both apparatuses, we see a similar small offset in the results at 300 K. Our rate coefficients are slightly smaller at 300 K than those of Timonen and Gutman. Our current results, as well as results of the previous CH 3 ● + Cl 2 and C 2 H 5 ● + Cl 2 reaction measurements, agree exceedingly well with other available measured results.…”

“…An important part of the motivation behind this work was to better understand the factors affecting chemical reactivity of carbon‐centered radicals. In a previous work , we studied the kinetics of C 2 H 5 ● , n ‐C 3 H 7 ● + Cl 2 , and n ‐C 4 H 9 ● + Cl 2 radicals with molecular chlorine and observed that n ‐butyl radicals reacted slightly faster than n ‐propyl radicals, which in turn reacted slightly faster than ethyl radicals. In this work, we have varied the structure of the hydrocarbon radical even more to see how it affects the value of the rate coefficient.…”

“…Because the corresponding absolute rate coefficients for the molecular oxygen reactions are known , we can compare our results with the results of Tyndall and coworkers. Several studies have been done on the related reactions CH 3 ● + Cl 2 and C 2 H 5 ● + Cl 2 , whose results will also be used in the discussion of reactivity trends.…”

Experimental and Modeling Study of the Temperature and Pressure Dependence of the Reaction C2H5 + O2 (+ M) → C2H5O2 (+ M)

“…We note that an onset of a decline of k 1 due to diffusion control at the highest pressures, such as seen for benzyl dimerization in ref 22, was not yet observed. Our second series of experiments was performed at Helsinki in a flow system using laser photolysis and photoionization mass spectrometry such as described in detail in ref 24. Experiments were done over the temperature range 188−298 K in the bath gas He.…”