Banca de DEFESA: TATIANE NICOLA TEJERO

PROPOSAL OF A KINETIC MODEL OF OXIDATION OF HYDROCARBONS AND SULPHURY COMPOUNDS IN THE TROPOSPHERE

KINPRO, rate coefficients, OH radical reactions, Dimethylsulfide, 1-pentene

In recent decades, several programs have been developed with the aim of calculating rate coefficients for uni and bimolecular reactions, such as the Multiwell and POLYRATE programs, being the second the most used. Despite the excellent performance of these programs in the calculation of rate coefficients, the need to investigate special cases such as dissociation reactions and complex mechanisms instigate the development of new programs. KINPRO is a package composed of several computational codes in order to perform calculations of kinetic parameters based on the conventional or variational transition state theory. It includes KINP pre-processing facilities plus other programs like KDIS, KUNI and MULTI, as well as KCVT, which is the canonical rate coefficients calculation program. The mechanisms obtained through theoretical calculations of the reaction of 1-pentene + OH radical and the oxidation of dimethylsulfide and its possible products were used to validate these programs. For the description of the mechanisms, GAUSSIAN 09 and ORCA programs were used. The addition of OH radicals to 1-pentene, described at the M06-2X/aug-cc-pVDZ level, allowing the study a small but complex system from the point of view of the multiplicity of conformers and reaction pathways, and to explain the non-Arrhenius behavior of experimentally observed global rate coefficients. Once dimethylsulfide enters the troposphere, it reacts with atmospheric oxidants, such as the OH or O3 radical, the former being described as preferential, due to its higher reactivity. This oxidation leads to the formation of various sulfur products that act as cloud condensation nuclei formers and will directly interfere with the temperature of the region. Therefore, there is a great interest in studies involving accurate forecasting of climatological events and, although there are several experimental works, there is not a wide range of theoretical works in this area. This work aims at developing a mechanism for the reactions between DMS and the OH radical and other sulfur compounds that are formed and to develop the kinetics of these reactions. To create this model, around 67 reactions were selected and theoretical calculations at the M06-2X/aug-cc-pVTZ theory level were made. Among these there are several uni and bimolecular reactions which opens space for a large number of tests. The results suggest that the computational implementations were successful, generating higher quality results than those that had already been calculated. The package is finally recommended for research in Theoretical Chemical Kinetics.