Reaction probabilities, cross sections, and threshold energies in the reaction of isotopically pure H atoms and n-butane

Abstract

Reaction cross sections and threshold energies have been determined for the first time for the isotopically pure reaction, H+n-C4H10→H2+C4H9, for abstraction from both the primary and secondary C–H bonds. Reaction probabilities were measured for H atoms at selected initial energies up to 112 kJ mol−1 by a photochemical method. With these results and the data for Xe moderated systems, together with new calculations of H–Xe collision densities by a stochastic method, it was possible to evaluate the cross sections and the corresponding reaction rate coefficients. Cross sections rose from threshold energies of 31±5 and 49±5 kJ mol−1 for secondary and primary abstraction, respectively, to ∼9×10−4 nm2 per secondary C–H bond and ∼5×10−4 nm2 per primary C–H bond at around 100 kJ mol−1. These cross sections are somewhat lower than those for secondary C–H bond in propane, and primary C–H bonds in propane and in ethane, but all are considerably smaller than the total collisional cross section.