title: Ab initio study of the role of entropy in the kinetics of acetylene production in filament-assisted diamond growth environments.
abstract: We present a new theoretical strategy, ab initio rate constants plus integration of rate equations, that is used to characterize the role of entropy in driving high-temperature/low-pressure hydrocarbon chemical kinetics typical of filament-assisted diamond growth environments. Twelve elementary processes were analyzed that produce a viable pathway for converting methane in a feed gas to acetylene. These calculations clearly relate the kinetics of this conversion to the properties of individual species, demonstrating that (1) loss of translational entropy restricts addition of hydrogen (and other radical species) to unsaturated carbon-carbon bonds, (2) rotational entropy determines the direction of the rate-limiting abstraction reactions, and (3) the overall pathway is enhanced by high beta-scission reaction rates driven by translational entropy. These results suggest that the proposed strategy is likely applicable to understand gas-phase chemistry occurring in the systems of combustion and other chemical vapor depositions.
authors.affiliation: Department of Materials Science and Engineering, North Carolina State University, Raleigh, North Carolina 27695-7907, USA. yanxinl@hotmail.com
authors.forename: Yanxin
authors.initials: Y
authors.lastname: Li
authors.forename: Donald W
authors.initials: DW
authors.lastname: Brenner
authors.forename: Xialan
authors.initials: X
authors.lastname: Dong
authors.forename: Chiachung
authors.initials: C
authors.lastname: Sun
mesh_terms: D000480:Alkynes / Q000138:chemical synthesis* / Q000737:chemistry; D018130:Diamond / Q000737:chemistry; D019277:Entropy; D005609:Free Radicals / Q000737:chemistry; D006859:Hydrogen / Q000737:chemistry; D007700:Kinetics; D008697:Methane / Q000737:chemistry; D008956:Models, Chemical; D011312:Pressure; D011789:Quantum Theory; D013696:Temperature
chemical_list: D000480:Alkynes; D005609:Free Radicals; D018130:Diamond; D006859:Hydrogen; D008697:Methane