title: Thermochemical and Kinetics of CH3SH + H Reactions: The Sensitivity of Coupling the Low and High-Level Methodologies.
abstract: The reaction system formed by the methanethiol molecule (CH3SH) and a hydrogen atom was studied via three elementary reactions, two hydrogen abstractions and the C-S bond cleavage (CH3SH + H → CH3S + H2(R1); → CH2SH + H2(R2); → CH3+ H2S (R3)). The stable structures were optimized with various methodologies of the density functional theory and the MP2 method. Two minimum energy paths for each elementary reaction were built using the BB1K and MP2 methodologies, and the electronic properties on the reactants, products, and saddle points were improved with coupled cluster theory with single, double, and connected triple excitations (CCSD(T)) calculations. The sensitivity of coupling the low and high-level methods to calculate the thermochemical and rate constants were analyzed. The thermal rate constants were obtained by means of the improved canonical variational theory (ICVT) and the tunneling corrections were included with the small curvature tunneling (SCT) approach. Our results are in agreement with the previous experimental measurements and the calculated branching ratio for R1:R2:R3 is equal to 0.96:0:0.04, with kR1= 9.64 × 10-13cm3molecule-1s-1at 298 K.
authors.affiliation: Departamento de Química, Instituto Tecnológico de Aeronáutica , São José dos Campos, 12.228-900, São Paulo, Brazil.
authors.forename: Daniely V V
authors.initials: DV
authors.lastname: Cardoso
authors.affiliation: Departamento de Química, Instituto Tecnológico de Aeronáutica , São José dos Campos, 12.228-900, São Paulo, Brazil.
authors.forename: Leonardo A
authors.initials: LA
authors.lastname: Cunha
authors.affiliation: Departamento de Física, Universidade Federal do Espírito Santo , Vitória, 29.075-910, Espírito Santo, 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: Corey A
authors.initials: CA
authors.lastname: Petty
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.identifier: http://orcid.org/0000-0003-1294-8707
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: Departamento de Química, Instituto Tecnológico de Aeronáutica , São José dos Campos, 12.228-900, São Paulo, Brazil.
authors.forename: Francisco B C
authors.identifier: http://orcid.org/0000-0002-2064-3463
authors.initials: FB
authors.lastname: Machado