Thermochemical and Kinetic Investigation of CH₃NH₂ Production in Titan's Atmosphere

The atmosphere of Titan is predominantly composed of nitrogen-, methane-, and carbon-based compounds. When exposed to energy sources such as solar radiation, these species can undergo complex chemical transformations, leading to the formation of organic molecules, such as methylamine, as well as its photodissociation. The present study aims to investigate the thermochemical and kinetic properties of elementary reactions involved in the production of methylamine (CH₃NH₂) over a temperature range of 75 to 300 K employing reliable electronic structure and chemical kinetics methods. The first reaction pathway (R_a) initiates with the reactants CH₂ and NH₂, yielding CH₂NH₂ (CH₂ + NH₂ → CH₂NH₂, R _a1) without an activation barrier. The formed CH₂NH₂ can further react with NH, leading to the formation of CH₃NH₂ and N (CH₂NH₂ + NH → CH₃NH₂ + N, R _a2), if it overcomes a barrier of 25.5 kJ·mol^-1. The second reaction pathway (R_b) involves the reactants CH₃ and NH, producing CH₃NH (CH₃ + NH → CH₃NH, R _b1), also without an activation barrier. This species can later react with NH to produce CH₃NH₂ and N (CH₃NH + NH → CH₃NH₂ + N, R _b2), as long as they overcome an energy barrier of 16.1 kJ·mol^-1. The rate coefficients calculated at 100 K are 3.6 × 10^-9 and 2.5 × 10^-18 cm³·molecule^-1·s^-1 for the consecutive reactions R _a1 and R _a2, respectively, and 3.8 × 10^-9 and 6.5 × 10^-17 cm³·molecule^-1·s^-1 for the consecutive reactions R _b1 and R _b2, respectively. Our results contribute to the modeling of Titan's atmosphere (and such environments), enabling the production of the CH₂NH₂ and CH₃NH radicals that may participate in other reactions for the production of more complex hydrocarbons and nitrogen compounds, as well as an alternative feasible mechanism for the production of methylamine.