KINETICS OF C1 ATOM REACTIONS WITH METHANE, ETHANE, AND PROPANE FROM 292 TO 800 K

Absolute rate coefficients for the reactions of chlorine atom with met hane and ethane between 292 and 800 K and with propane between 292 and 700 K have been determined using the laser photolysis/continuous wave infrared long-path absorption method, LP/cwIRLPA. A novel reactor des ign and optical arrangement allow long absorption paths with precise c ontrol of the temperature in the probed volume. The rate coefficient f or methane exhibits significant curvature between 292 and 800 K and ca n be described over this temperature range by a modified Arrhenius exp ression, k(CH4)(T) = [3.7((-2.5) (+8.2)) x 10(-13) cm(3) molecule(-1) s(-1)](T/298)(2.6(+/-0.7)) exp[-385(+/-320)/T] (all error bars are +/- 2 sigma precision only). In the temperature range 292-600 K the rate w ith ethane agrees well with earlier investigations, fitting a simple A rrhenius expression k(C2H6)(T) = 8.6(+/-0.5) x 10(-11) exp[-135(+/-26) /T] cm(3) molecule(-1) s(-1). However, as the temperature increases be yond 600 K the Arrhenius plot exhibits significant upward curvature. O ver the range 292-800 K a three-parameter Arrhenius fit, k(C2H6)(T) = 3.4(+/-1.4) x 10(-11) (T/298)(0.7(+/-0.3)) exp[150(+/-110)/T] cm(3) mo lecule(-1) s(-1), models the experimental data adequately. The rate co efficient for propane is found to be independent of temperature and eq ual to 1.38(+/-0.03) x 10(-10) cm(3) molecule(-1) s(-1).