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 laser 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) molecule(-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 dependence is in good agreement with previous determinations of this reaction, and is consistent with barrierless formation of an excited C3H5 adduct followed by rapid decomposition. The kinetic isotope effect for deuteration of the CH radical is k(1)/k(2) = 1.19 +/- 0.04 at room temperature, and declines 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 independent of temperature over the range studied. Quantum chemical calculations of the reaction path indicate that the reaction is dominated by addition, with a minor role possible for insertion.