Kinetics of CCN Radical Reactions with a Series of Normal Alkanes

Abstract

The reactions of CCN(X̃2Πi) radicals with normal alkanes have been studied at about 10 Torr total pressure and room temperature using the pulse laser photolysis/laser-induced fluorescence technique. CCN (X̃2Πi) radicals are generated by the fourth harmonic of a Nd:YAG laser photolysis of Cl3CCN at 266 nm. The relative concentration of CCN (X̃2Πi) radicals was monitored in the (0−0) band of the CCN (Ã2Δ ← X̃2Πi) transition at 470.9 nm by laser induced fluorescence (LIF). From the analysis of the relative concentration−time behavior of CCN (X̃2Πi) under pseudo-first-order conditions, the rate constants for the reaction of CCN (X̃2Πi) with a series of normal alkanes (C1−C8) were determined for the first time. The new data establish that the gas-phase reactivity of small alkanes (C1−C8) towards the CCN radicals follows the linear free energy relationship typical of hydrogen abstraction. A comparison with the corresponding reactions of CN and OH radicals with a series of normal alkanes, leads us to suggest that the reaction of CCN (X̃2Πi) with small normal alkanes proceeds via the mechanism of hydrogen abstraction. The plausibility of the suggested reaction mechanism is strengthened by bond dissociation energy (BDE) correlations and linear free energy correlations.