Resonances in low-energy electron scattering from <i>para</i>-benzoquinone

We present detailed ab initio scattering calculations for electron collisions with para-benzoquinone. The R-matrix method has been used to study elastic and electronically inelastic scattering. We have identified 25 resonances of shape, Feshbach, core-excited shape and mixed character between 0 and 8 eV. Agreement of our resonance spectrum with existing literature is discussed, in particular that of the low-lying resonances that participate in the photodetachment process. Integral elastic and total inelastic cross sections are also presented

Study of Low-energy Electron Collisions with Molecules of Biological Relevance

This thesis is focused on the application of the R-matrix method, as implemented in the UKRmol and UKRmol+ suites, to study low-energy electron collisions with three medium-sized molecules of biological relevance: para-benzoquinone, thiophene and alanine. Our goals for all the targets are mainly three: (i) to identify and characterize respective resonances; (ii) to calculate elastic and inelastic integral and elastic differential cross sections; and (iii) compare our results with the literature. To do so, we use several scattering models, choosing the most suitable on the basis of the characteristics being investigated: Static Exchange, Static Exchange plus Polarization and/or Close-Coupling approximation. Specially at higher energies, we find an unexpectedly large number of resonances for the three targets, most of them of core-excited and core-excited shape character. We compare our results with other calculations and/or experiments in the literature, but the absence of detailed experimental results for many targets at these energies precludes a meaningful comparison. Nonetheless, three scenarios are then obtained: in the first one, for para-benzoquinone, the agreement with previous results is satisfactory; in the second, for thiophene, is excellent; and finally, for alanine, there is not much prior information on the literature to make decisive conclusions. This work was all published in peer-reviewed journals

Shape and core-excited resonances in electron scattering from alanine

We present detailed ab initio scattering calculations using the R-matrix method for electron collisions with the most stable conformer of α-alanine. The shape resonances that we identify are in good agreement with earlier calculations and experiments. Core-excited and mixed-character resonances are identified and characterized computationally for the first time. Dissociative electron attachment results are discussed in relation to the resonances identified

Shape and Core-Excited Resonances in Thiophene

We present a comprehensive study of resonance formation in electron collisions with thiophene. Detailed calculations have been performed using the ab initio R-matrix method. Three shape resonances previously described, two of π* character and one σ*, as well as a number of resonances of core-excited or mixed character are identified and characterized. Differential cross sections for electron impact excitation up to 18~eV and for two scattering angles, 90° and 135°, are measured. The measured cross sections provide experimental confirmation for a number of the core-excited resonances. The link between these resonances and prior DEA experiments is discusse

Cross sections for electron scattering from thiophene for a broad energy range

We present cross sections for elastic and inelastic electron scattering from thiophene calculated in the energy range 0.1-1000 eV. The R-matrix and independent atom representation-screening-corrected additivity rule (IAM-SCAR) methods were used for low-energy and intermediate and high scattering energies, respectively. The results provide a consistent picture of the scattering process in the whole energy range. The effect of including an interference term in the IAM-SCAR approach is considered. Agreement with prior theoretical results is also discussed

Racionalização do mecanismo de adição de compostos carbonílicos a vinil-mono e di-sulfonas, catalisada por aminas

As sulfonas são conhecidas pelos químicos orgânicos pela sua versatilidade sintética e actividade biológica, nomeadamente os fármacos conhecidos por sulfa drugs, extremamente importantes em química medicinal. As vinil-sulfonas constituem uma sub-família das sulfonas e têm demonstrado ao longo do tempo a sua capacidade de inibir diversos processos enzimáticos, introduzindo propriedades biológicas únicas. Do ponto de vista sintético, o método mais directo para obter estes compostos é via redução dos produtos de adição de Michael a vinil-di-sulfonas, o que não é favorável em termos de economia de átomos. Por outro lado, o mecanismo da reacção de adição de Michael de compostos carbonílicos a vinil-sulfonas tem levantado algumas dúvidas, devido à existência de dois possíveis mecanismos reacionais. O objectivo principal desta dissertação é racionalizar o mecanismo de adição de compostos carbonílicos a vinil-mono e di-sulfonas, recorrendo a estudos teóricos de DFT e experimentais, incluindo RMN. Foram considerados os mecanismos via intermediário enamina e via catálise básica, e através de estudos de RMN foi possível retirar conclusões sobre as velocidades relativas das reacções, bem como meio de comprovar a formação de alguns produtos. Os resultados teóricos obtidos revelam que, para as mono-sulfonas, o mecanismo via enamina é mais favorável energeticamente. No entanto, a existência de reacções competitivas de energia de activação mais baixa não permitem obter o produto desejado. Para eliminar estas reacções, utilizam-se aminas terciárias e a reacção segue um mecanismo via catálise básica. O estudo dos coeficientes da orbital HOMO dos compostos carbonílicos revelou que a localização do enol é um factor determinante para estas reacções. Por outro lado, os resultados obtidos revelaram que as di-sulfonas sendo extremamente reactivas, podem adoptar qualquer um dos caminhos reacionais, em função do catalisador escolhido, e não são sensíveis ao substrato. Neste caso, as reacções competitivas que ocorrem são reversíveis,e o produto de adição conjugada é sempre favorecido. Estudou-se ainda, teoricamente, a reacção de adição a mono-sulfonas de forma intramolecular, que apresenta claramente um mecanismo via enamina, cuja energia de activação é mais baixa que a respectiva adição competitiva