Estudio de posibles precursores comunes para la formación de formamida y acetamida en granos de polvo-hielo de agua.
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Date
2024
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Universidad de Concepción
Abstract
La formamida (NH2CHO) en el medio interestelar (ISM) es de gran interés en la astroquímica por su relevancia como precursor biótico. Un estudio reciente de Ligterink et al.1 apunta a una correlación entre las concentraciones de esta molécula y la acetamida (CH3C(O)NH2), posicionando a esta como otra especie de interés. En esta Tesis de Magíster se estudiaron dos posibles caminos de reacción radical-neutro para la formación de formamida a partir de la adición HCN + ·OH y de la adición H2O + ·CN, y un posible camino de formación para la acetamida a partir de la adición CH3CN + ·OH. Este estudio computacional se llevó a cabo en la fase gas, en presencia de dos moléculas de agua y en un clúster de 22 moléculas de agua. Los métodos utilizados fueron BhandHlyp/def2-svp para los cálculos
geométricos y BMK-D3BJ/def2-tzvp para los cálculos energéticos. De estas reacciones se distinguieron tres pasos; adición radical-neutra, tautomerización y extracción de un hidrógeno desde una molécula de agua. Se observó que las moléculas de agua presentan su mayor efecto catalítico durante la tautomerización gracias al relé de hidrógeno. En el clúster de agua solo se estudió la adición y tautomerización. Las reacciones de HCN + ·OH para formar formamilo y CH3CN + ·OH para formar acetamilo son termodinámicamente viables en el ISM si y solo si la energía liberada por
el primer paso exotérmico se logra transferir al resto de la reacción. La reacción de H2O + ·CN para formar formamilo no es viable en el clúster por presentar una barrera inicial de 70.6 kJ/mol.
Formamide (NH2CHO) in the interstellar medium (ISM) is of high interest in astrochemistry given its relevancy has a bio-precursor. A recent study by Ligterink et al.1 points at a correlation between the concentrations of said molecule and acetamide (CH3C(O)NH2), putting it as a molecule of interest. In this Master’s thesis two possible radical-neutral formation paths where studied for formamide; the addition HCN + ·OH and the addition H2O + ·CN, and one for acetamide; the addition CH3CN + ·OH. This computational study was done in the gas phase, in the presence of 2 non reactive water molecules and on a 22 water molecule clúster. The methods used in this work where BhandHlyp/def2-svp for the geometry calculations and BMK-D3BJ/def2-tzvp for the energy calculations. From this reactions three steps where distinguish; radical-neutral addition, tautomerization and the extraction of a hydrogen from a water molecule. It was observed that the water molecules have a big catalytic effect during tautomerization thanks to h-relay. In the 22 water molecules system only the addition and tautomerization where studied. The HCN + ·OH reaction to obtain formamyl and the CH3CN + ·OH reaction to obtain acetamyl are thermodynamicly viable in the ISM only if the energy released in the first step is able to carry to the rest of the reaction. The H2O + ·CN reaction to obtain formamyl is not viable in the ice clúster given its 70.6 kJ/mol barrier for the first step.
Formamide (NH2CHO) in the interstellar medium (ISM) is of high interest in astrochemistry given its relevancy has a bio-precursor. A recent study by Ligterink et al.1 points at a correlation between the concentrations of said molecule and acetamide (CH3C(O)NH2), putting it as a molecule of interest. In this Master’s thesis two possible radical-neutral formation paths where studied for formamide; the addition HCN + ·OH and the addition H2O + ·CN, and one for acetamide; the addition CH3CN + ·OH. This computational study was done in the gas phase, in the presence of 2 non reactive water molecules and on a 22 water molecule clúster. The methods used in this work where BhandHlyp/def2-svp for the geometry calculations and BMK-D3BJ/def2-tzvp for the energy calculations. From this reactions three steps where distinguish; radical-neutral addition, tautomerization and the extraction of a hydrogen from a water molecule. It was observed that the water molecules have a big catalytic effect during tautomerization thanks to h-relay. In the 22 water molecules system only the addition and tautomerization where studied. The HCN + ·OH reaction to obtain formamyl and the CH3CN + ·OH reaction to obtain acetamyl are thermodynamicly viable in the ISM only if the energy released in the first step is able to carry to the rest of the reaction. The H2O + ·CN reaction to obtain formamyl is not viable in the ice clúster given its 70.6 kJ/mol barrier for the first step.
Description
Tesis presentada para optar al grado de Magíster en Ciencias con Mención en Química.
Keywords
Agua, Formamida, Acetamida