Glicoaldeído no meio interestelar: proposta de mecanismo químico de formação e análise teórica acerca de sua viabilidade termodinâmica

Abstract

Astrochemistry is a scientific field that stands out for the identification and study of chemical processes in the interstellar medium (ISM), with one of its main objects of study being complex organic molecules, which are generally associated with biomolecule synthesis processes. With this in mind, glycolaldehyde (GA) becomes the focus of this work due to its possible connections to reaction processes associated with prebiotic chemistry. Furthermore, the precursor used for a possible route to the synthesis of GA was ethanol, an alcohol already detected in the ISM and with a possible abundance correlation with GA itself. Thus, a four-step reaction mechanism was proposed, and the energetic feasibility of the proposal was analyzed through thermodynamic parameters of the reactions. These data were obtained using the theoretical methods DFT and CCSD(T), based on the M06-2X functional and the aug-cc-pVTZ basis set. The combined level of theory was denoted as CCSD(T)//M06-2X/cc-pVTZ. Based on this level of theory, several types of calculations were performed in order to obtain thermodynamic parameters for the system. The combined level of theory demonstrated superiority in the results, given the effectiveness of CCSD(T) for systems involving weakly localized radicals. Thus, based on the analysis of the thermodynamic data, steps 1, 2.1, and 4 exhibited considerable energy barriers along with an endothermic character for the reactions, while step 3, in addition to being exothermic, maintained a lower barrier than the other steps. Furthermore, step 2 did not yield results due to the inefficacy of the optimizations of the proposed stationary states. Therefore, in view of the thermodynamic data, the considered mechanism, and the extreme conditions employed, the theoretical analysis of the synthesis of glycolaldehyde from ethanol resulted in the infeasibility of the process.