MOLECULAR STRUCTURE

Author: CASADESÚS CASTRO RICARD.
Year: 2004.
University: AUTÓNOMA DE BARCELONA [www.uab.es].
Place of defense: FACULTAT DE CIÉNCIES.
Place of preparation: ESCUELA DE POSTGRADO.

Summary: In this dissertation have developed several theoretical studies focusing on transfers protónicas fotoinducidas (PIPT, PhotoInduced Proton Transfer), studied primarily in electronic excited states, a subject of much debate currently in the field of quantum electronics calculations. In general, it has deepened the understanding of the factors that govern chemical reactions to understand the theoretical underpinnings for the purpose of being able to control the chemical processes and design of new acquaintances. In this regard, this study aims precisely to demonstrate the effect of environment on the reactions of intra-and intermolecular transfer protónica in electronic excited states. The possibility of studying this kind of reaction opens the door to supramolecular design environments that help or hinder these transfers hydrogen. Such reactions are part of almost any complex chemical process, including almost all biological cycles. This explains the great interest they have attracted in recent years. It also conducted a theoretical study of the kinetic isotope effect (KIE, Kinetic Isotopo Effect) in the excited state by deuteración some protons, calculating the respective constant speed from the theory microcanónica state of transition, after developing a program computer.

Author: CASANUEVA SOLÓRZANO JORGE.
Year: 2004.
University: AUTÓNOMA DE MADRID [www.uam.es].
Place of defense: AUTÓNOMA DE MADRID.
Place of preparation: DEPARTAMENTOS DE QUÍMICA FÍSICA APLICA,UNIVERSIDAD AUTÓNOMA DE MADRID.

Summary: Methodologies have been developed to predict espín - espín coupling constants (J) Resonance Magnétíca Nuclear (NMR) quite exactítud from theoretical calculations minímizando the computational cost. For small molecules have been calculated coupling constants without significant loss of accuracy using the base functions BS2 and an additive method developed for the method of field autoconsistente ulticonfiguracional (MCSCF). The base BS2 has developed specific mind to calculate constant coupling between the atoms of carbon, nitrogen, oxygen, and hydrogen fluoride. The additive method to estimate the contribution of the electronic correlation total from individual contributions. The vibrational contributions are the same order of magnitude as the differences between the experimental and coupling constant coupling constants calculated for the molecular geometry of balance. Its inclusion in the calculations improvement, in general, the agreement between the calculated and experimental couplings deviations but remain higher than the experimental errors. For molecules of practical interest has developed a methodology for predicting the constant coupling neighborhood protón-protón quite accurately from calculations of the theory of functional density (DFT) using functional B3L YP And optimizing base BHH functions suitable for the calculation of constant coupling between proton. For a package of 163 links from etanos replaced and derivatives of cyclohexane norbornano and ciclopropano the discrepancy between the calculated and experimental values is 0.2 Hz.

Author: DIAZ TENDERO VICTORIA SERGIO.
Year: 2004.
University: AUTÓNOMA DE MADRID [www.uam.es].
Place of defense: FACULTAD DE CIENCIAS.
Place of preparation: FACULTAD DE CIENCIAS (UAM).

Summary: This thesis presents the theoretical study of the structure and fragmentation of small aggregates of carbon and fullerenes neutral and positively charged. The study of small aggregates of carbon (Cnq +, n = 2-9, q = 0.1 and 2) has been approached from two different perspectives but intimately interrelated. First has described the electronic structure, geometry and vibrational properties of aggregates neutral, simple and doubly charged. This has enabled assess the stability of the different isomers and variation in the properties as the energy of dissociation and ionization potential of the burden and size. Subsequently has conducted a study of the dynamics of fragmentation of aggregates neutral through simulations based on the statistical mechanics. This would have evaluated what were the main factors influencing the stability and fragmentation of small aggregates of carbon. The main problem in the study of fullerenes lies in the large number of isomers showing. To cope, it has proposed a strategy for selecting confórmeros more stable from the fragmentation of C60. Subsequently has conducted a systematic study of the structure of the neutral species and positively charged with sizes between 50 and 60 atoms and highly charged fullerenes (C60q + and C58q +). We have evaluated the energies of dissociation and ionization potentials depending on the size and the load of fullerene. It has been estimated in turn limit Coulombiano of C60, ie the burden greater than it can bear without added fragmented spontaneously. Finally has been studied in detail the structure of fullerenes generated by evaporation of C2 and the factors that influence the stability of different isomers. Analysis of the results of structure has been carried out to assess various factors such as the number and type of rings and their relative positions in the structure, aromatic local and global, sphericity and the types of DC link. The theoretical methods utlizados for the study of electronic structure and geometry are based on the theory of functional density (DFT). In particular has been used functional hybrid B3LYP. In the case of small aggregates of carbon have been turn calculations at Coupled Cluster including single and double excitation and the excitation triple so perturbativa, CCSD (T). This has been able to corroborate the validity of the results B3LYP. To study the fragmentation two methodologies have been developed based on statistical mechanics. The first of these is the integration hasa time given a set of equations kinetic aclopadas. The constant evaporation rate shown in these equations have been evaluated with the theory microcanónica of Weisskopf for energy deposited in the aggregate. Subsequently were carried out simulations with the method microcanónico Metropolis MonteCarlo. In these simulations one moves into a phase space into a region with maximum entropy. Then, the physical observable is measured as an average statistic in this region of highest probability for an internal energy system. The necessary data entered in both approaches (dissociation energies, geometries, frequency vibrations, etc.). Have been taken from the res 8 ultados 4bb obtained with calculations structure. In the case of fullerenes have been carried out Hartree - Fock calculations, MÃ ¶ ller-Plesset of second order and B3LYP with different bases. It has been proven the importance of including the electronic correlation and increase based on the calculation. Therefore, in this thesis presents a systematic study of the properties of small aggregates of carbon and fullerenes with different methodologies. On display are the main factors that determine the structure and geometry of these molecules and stability in the face of fragmentation.