title: Thermochemical and Kinetics of Hydrazine Dehydrogenation by an Oxygen Atom in Hydrazine-Rich Systems: A Dimer Model.
abstract: The kinetics of the reaction of N2H4 with oxygen depends sensitively on the initial conditions used. In oxygen-rich systems, the rate constant shows a conventional positive temperature dependence, while in hydrazine-rich setups the dependence is negative in certain temperature ranges. In this study, a theoretical model is presented that adequately reproduces the experimental results trend and values for hydrazine-rich environment, consisting of the hydrogen abstraction from the hydrazine (N2H4) dimer by an oxygen atom. The thermochemical properties of the reaction were computed using two quantum chemical approaches, the coupled cluster theory with single, double, and noniterative triple excitations (CCSD(T)) and the M06-2X DFT approach with the aug-cc-pVTZ and the maug-cc-pVTZ basis sets, respectively. The kinetic data were calculated with the improved canonical variational theory (ICVT) using a dual-level methodology to build the reaction path. The tunneling effects were considered by means of the small curvature tunneling (SCT) approximation. Potential wells on both sides of the reaction ((N2H4)2 + O → N2H4···N2H3 + OH) were determined. A reaction path with a negative activation energy was found leading, in the temperature range of 250-423 K, to a negative dependence of the rate constant on the temperature, which is in good agreement with the experimental measurements. Therefore, the consideration of the hydrazine dimer model provides significantly improved agreement with the experimental data and should be included in the mechanism of the global N2H4 combustion process, as it can be particularly important in hydrazine-rich systems.
authors.affiliation: Departamento de Química, Instituto Tecnológico de Aeronáutica , São José dos Campos, 12.228-900 São Paulo, Brazil.
authors.forename: Rene F K
authors.initials: RF
authors.lastname: Spada
authors.affiliation: Departamento de Química, Instituto Tecnológico de Aeronáutica , São José dos Campos, 12.228-900 São Paulo, Brazil.
authors.forename: Luiz F A
authors.initials: LF
authors.lastname: Ferrão
authors.affiliation: Divisão de Aerotermodinâmica e Hipersônica, Instituto de Estudos Avançados , São José dos Campos, 12.228-001 São Paulo, Brazil.
authors.forename: Orlando
authors.initials: O
authors.lastname: Roberto-Neto
authors.affiliation: Department of Chemistry and Biochemistry, Texas Tech University , Lubbock, Texas 79409-1061, United States.|Institute for Theoretical Chemistry, University of Vienna , A-1090 Vienna, Austria.|School of Pharmaceutical Sciences and Technology, Tianjin University , Tianjin 300072, People's Republic of China.
authors.forename: Hans
authors.initials: H
authors.lastname: Lischka
authors.affiliation: Departamento de Química, Instituto Tecnológico de Aeronáutica , São José dos Campos, 12.228-900 São Paulo, Brazil.
authors.forename: Francisco B C
authors.initials: FB
authors.lastname: Machado
mesh_terms: D019281:Dimerization; D006834:Hydrazines / Q000737:chemistry*; D006865:Hydrogenation; D007700:Kinetics; D010100:Oxygen / Q000737:chemistry*; D011789:Quantum Theory; D013696:Temperature
chemical_list: D006834:Hydrazines; C029424:hydrazine; D010100:Oxygen