Reactions of C2(a 3Pi(u)) with selected saturated alkanes: a temperature dependence study.

We present a temperature dependence study on the gas phase reactions of the C(2)(a (3)Pi(u)) radical with a selected series of saturated alkanes (C(2)H(6), C(3)H(8), n-C(4)H(10), i-C(4)H(10), and n-C(6)H(14)) by means of pulsed laser photolysis/laser-induced fluorescence technique. The bimolecular rate constants for these reactions were obtained between 298 and 673 K. A pronounced negative temperature effect was observed for n-C(4)H(10), i-C(4)H(10), and n-C(6)H(14) and interpreted in terms of steric hindrance of the more reactive secondary or tertiary C-H bonds by less reactive CH(3) groups. Detailed analysis of our experimental results reveals quantitatively the temperature dependence of reactivities for the primary, secondary, and tertiary C-H bonds in these saturated alkanes and further lends support to a mechanism of hydrogen abstraction.