Temperature dependence and deuterium kinetic isotope effects in the CH(CD)+C2H4(C2D4) reaction between 295 and 726 K

Absolute rate coefficients for the reactions CH + C2H4 (k(1)), CD + C2H4 (k (2)), CH + C2D4 (k(3)), and CD + C2D4 (k(4)) have been measured by the lase r photolysis/CW laser-induced fluorescence method at temperatures from 295 to 726 K. The individual rate coefficients can be described by k(1) = (2.85 +/- 0.02) (T/293)(-(0.31) (+/-) (0.02)) x 10(-10) cm(3) molecule(-1) s(-1) , k(2) = (2.40 +/- 0.01) (T/293)(-(0.28) (+/- 0.01)) x 10(-10) cm(3) molecu le(-1) s(-1), k(3) = (2.61 +/- 0.01) (T/293)(-(0.34 +/- 0.01)) x 10(-10) cm (3) molecule(-1) s(-1), k(4) = (2.22 +/- 0.01) (T/293)(-(0.21 +/- 0.02)) x 10(-10) cm(3) molecule(-1) s(-1), where the error estimates are +/-2 sigma and reflect the precision of the fit. The slight negative temperature depen dence is in good agreement with previous determinations of this reaction, a nd is consistent with barrierless formation of an excited C3H5 adduct follo wed by rapid decomposition. The kinetic isotope effect for deuteration of t he CH radical is k(1)/k(2) = 1.19 +/- 0.04 at room temperature, and decline s somewhat with temperature. The kinetic isotope effect for deuteration of the ethylene is k(1)/k(3) = 1.08 +/- 0.04 at 290 K, and is approximately in dependent of temperature over the range studied. Quantum chemical calculati ons of the reaction path indicate that the reaction is dominated by additio n, with a minor role possible for insertion.