The reactions of hydrogen atoms with cyclo-C 3H 5 and cyclo-C 5H 9 radicals: Rates and mechanisms at low pressure

Abstract

The reactions of the cyclic hydrocarbon radicals c -C 3 H 5 and c -C 5 H 9 with hydrogen/deuterium atoms have been studied at low pressures (0.2–10 torr), using fast discharge flow reactors and a Laval nozzle reactor. Stable and labile species were determined by a mass spectrometer, using low ionization energy and synchronous ion counting; samples from the reaction center were withdrawn continuously via molecular beam sampling. The rate of the radical producing reactions were determined relative to standard reactions, leading to c -C 3 H 6 +Fproducts (1) k 1 =1.3 10 14 cm 3 /mols c -C 5 H 10 +F→products (3) k 3 =1.7 10 14 cm 3 /mols The rate constants of the radical+atom reactions were measured using the reaction D+C 2 H 5 as the standard: c -C 3 H 5 +D→products (5) k 5 =3 10 13 cm 3 /mols c -C 5 H 9 +D→products (7) k 7 =3.910 13 cm 3 /mols The mechanisms of the reactions were found to be D + c − C 3 H 5 → c − C 3 H 5 D * c − C 3 H 5 D * → C 3 H 5 D * C 3 H 5 D * → M C 3 H 5 D → C 3 H 4 D + H D + c − C 5 H 9 → c − C 5 H 9 D * c − C 5 H 9 D * → M c − C 5 H 9 D These mechanisms (association, isomerization, decomposition/stabilization) are discussed, using unimolecular rate theory.