Efeito de ligação de hidrogênio em propriedades de aglomerados de moléculas interestelares.

Abstract

The interstellar médium (ISM) is a gigantic reservoir of gases and particles, in general, that are concentrated in an enormously big region in space known as interstellar cloud. There exist huge interest in detecting and understanding better the elecronic structure of these interstellar molecules. With the ever growing development of highly sophisticated radio-astronomical instruments, approximately de 150 molecules have already been detected in space till date. Regarding this, it is of great importance for the astronomers to have some informations before hand obtained through theoretical calculations with respect to the structural properties, intermolecular interactions and spectroscopy of the 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 three molecules of astrophysical, astrochemical and astrobiological interest like Hydrogen Cyanide (HCN), Nytrosyl Hydride (HNO) and Formic acid (HCOOH. All these molecules have recently been detected in the interstellar space through radio astronomical measurements. The presence of hydrogen bonding leads to various alteration to the structural properties of the molecules involved in the cluster formation. It also provokes a redistribution of charges in the proton donor as well as in the proton receptor molecule and as a consequence dipole moment of the molecules might change which, in turn, modifies the electrical properties of the molecules. With this idea, we have focussed our attention in the present work on the following homogenous HCN ··· HCN, HNO···HNOHCOOH···HCOOH, and heterogeneous HCN···HNO, HCN···HCOOH, HNO···HCOOH clusters (dimers). Our objective is to investigate the changes in the structural properties, energetics (binding energy, deformation energy, zero-point vibrational energy), electrical properties (dipole moment, polarizability and Rayleigh scattering parameters) and also in thermodynamical (free energy) and spectroscopic (rotational e vibrational) properties of these clusters due to the hydrogen-bond formation. To perform the calculations , we have used high-level quantum chemical ab-initio methods like Hartree-Fock (HF) and Moller-Plesset perturbation theory with sufficiently large basis sets like 6-311++G(d,p) and Aug-cc-pVDZ.