Estudo teórico da fotoionização do orbital 15a

Abstract

Resumo: A alimentacao e parte essencial da vida humana. Alimentos sao preparados das mais inumeras formas, e dentre elas ha o que e chamado popularmente de fritagem, que encadeia reacoes responsaveis pela formacao de contaminantes cancerigenos, como a acroleina . O estudo da estrutura eletronica da molecula de acroleina pode ajudar a compreender melhor a dissociacao da molecula e possivelmente reduzir a quantidade ingerida, reduzindo casos de cancer causados por este contaminante. Neste trabalho, foi estudado o potencial de ionizacao da molecula de acroleina, utilizando geometrias calculadas pelo NIST e calculos nivel HF em moleculas neutras e UHF em ions, realizados no pacote computacional Gaussian09, revelou resultados para seus conformeros cis e trans nas bases 6-31G e 6-311++G**. Os valores de potencial de ionizacao obtidos foram de 8,313 eV e 8,277 eV, com erros relativos de 22,465% e 18,133% para cis e trans, respectivamente, na base 6-31G, e de 8,443 eV e 8,420 eV, com erros relativos de 21,256% e de 16,716% na cis e na trans, respectivamente na base 6-311++G**. Embora esses resultados sejam inferiores aos valores de referencia, destacam a influencia das bases double-zetta e triple-zetta com funcoes difusas nos orbitais de caroco no calculo do potencial de ionizacao da acroleina. Nestes calculos, foram obtidos valores de polarizabilidade da molecula [Alfa]xx = 44,603 D, [Alfa]yy = 28,022 D e [Alfa]zz = 5,567 D. Esses dados de polarizacao foram utilizados para gerar um arquivo de input no ePolyScat para a acroleina trans, onde secoes de choque de fotoionizacao e parametros de assimetria foram calculados para o orbital 15ah do isomero trans da acroleina. Observou-se que a transicao de simetria ah contribui significativamente, representando de 68% a 70% da secao de choque total, com picos entre 10,61 eV e 12,61 eV. Alem disso, uma analise qualitativa comparativa foi realizada entre resultados para secoes de choque e parametros de assimetria na aproximacao com e sem polaricao. Verificou-se uma pequena divergencia nos modelos de comprimento e velocidade de dipolo para energias superiores a aproximadamente 22 eV, enquanto as secoes de choque apresentaram uma diferenca perceptivel proxima ao potencial de ionizacao, com um pico notavel em torno de 11,10 eV

Abstract: Nutrition is an essential part of human life. Foods are prepared in countless ways, and among them is what is popularly known as frying, which triggers reactions responsible for the formation of carcinogenic contaminants, such as acrolein. Studying the electronic structure of the acrolein molecule can help better understand the molecule’s dissociation and possibly reduce the amount ingested, thereby decreasing cases of cancer caused by this contaminant. In this work, the ionization potential of the acrolein molecule was studied using geometries calculated by NIST and HF level calculations for neutral molecules and UHF for ions, performed with the Gaussian09 computational package. Results for its cis and trans isomers were obtained using the 6-31G and 6-311++G** basis sets. The obtained values were 8.313 eV and 8.277 eV, with relative errors of 22.465% and 18.133% for cis and trans, respectively, in the 6-31G basis set, and 8.443 eV and 8.420 eV, with relative errors of 16.716% for trans and 21.256% for cis in the 6-311++G** basis set. Although these results are lower than reference values, they highlight the influence of double-zetta and triple-zetta basis sets with diffuse functions on core orbitals in the calculation of acrolein’s ionization potential. In these calculations, polarization values of the molecule were obtained as [Alfa]xx = 44.604 D, [Alfa]yy = 28.022 D, and [Alfa]zz = 5.567 D. These polarization data were used to generate an input file in ePolyScat for transacrolein, where photoionization cross-sections and asymmetry parameters were calculated for the 15a" orbital of the trans isomer of acrolein. It was observed that the a" symmetry transition contributes significantly, representing 68% to 70% of the total cross-section, with peaks between 10.61 eV and 12.61 eV. Additionally, a comparative qualitative analysis was performed between results for cross-sections and asymmetry parameters in the approximation with and without polarization. A slight divergence was noted in the dipole lenght and velocity models for energies above approximately 22 eV, while the cross-sections showed a noticeable difference near the ionization potential, with a notable peak around 11.10 eV