A Low Temperature Study of the Reactions of Atomic Chlorine with Simple Alkanes

Abstract

The kinetics of the reactions of atomic chlorine with ethane and propane have been studied in a continuous supersonic flow reactor over the range 48 K < or = T < or = 167 K. Chlorine atoms were produced by microwave discharge upstream of the Laval nozzle and were probed in the vacuum ultraviolet wavelength range around 138 nm by resonance fluorescence. The reaction of Cl with ethane has been found to exhibit a positive temperature dependence, with a rate coefficient decreasing from (4.3 +/- 0.6) x 10(-11) cm(3) molecule(-1) s(-1) at 167 K to (2.9 +/- 0.3) x 10(-11) cm(3) molecule(-1) s(-1) at 48 K and deviates from true Arrhenius behavior below 120 K. In contrast, the rate coefficient for the reaction of Cl with propane has been found to have a constant value of (1.4 +/- 0.2) x 10(-10) cm(3) molecule(-1) s(-1) over the same temperature range. The expressed uncertainties are the combined statistical (a single standard deviation from the mean) and systematic (estimated at 10%) uncertainties.