Propriedades eletrônicas e espectroscópicas de aglomerados de moléculas interestelares
Silva, Arnaldo Machado da
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The interstellar médium (ISM) is a gigantic reservoir of atoms and molecules of different shapes and sizes. In general, they are concentrated in enormously big regions in space known as interstellar cloud. There exist huge interest in detecting and understanding better the elecronic structure, properties and reaction pathways of these interstellar molecules. With the ever growing development of highly sophisticated radio-astronomical instruments, more than 150 molecules have already been detected in space till date. Regarding this, it is of great importance for the astronomers to have some informations beforehand, obtained through theoretical calculations, with respect to the structural properties, intermolecular interactions and spectroscopic properties of the individual molecules as well as of the clusters formed by these molecules. These informations make the analysis of experimental data easier, safer and productive. With this motivation, we would like to study, in this work, the hydrogen-bonded clusters formed by the welknown astromolecule Hydrogen Cyanide (HCN) with two other astrobiomolecules: Formic acid (HCOOH) and Glycine (NH2CH2COOH). All these three molecules have recently been detected in the interstellar space through radio astronomical measurements and are of great interest in astrophysics, astrochemistry and astrobiology. The presence of hydrogen bonding leads to various alteration in the structural properties of the molecules involved in the cluster formation. It also provokes a redistribution of charges in the próton donor as well as in the próton receptor molecule and as a consequence dipole moment of the molecules might change which, in turn, modifies the electric properties of the molecules. Spectroscopic properties also suffer alterations. With this idea, we have focussed our attention in the present doctoral work on the heterogenous hydrogen-bonded dimers: HCN ⋅⋅⋅ HCOOH and HCN⋅⋅⋅NH2CH2COOH and trimers: (HCN)2⋅⋅⋅HCOOH and (HCN)2⋅⋅⋅NH2CH2COOH in gas phase. The objective of the present work is to investigate the changes in the structural properties, energetics, electric properties (dipole moment, polarizability) using high-level quantum chemical methods like Moller-Plesset perturbation theory and Density Functional theory with appropriate and sufficiently large basis sets. The effect of hydrogen-bond formation on the vibrational and NMR spectra of these molecules has also been considered.