Assinatura molecular do aquecimento global: um estudo teórico de aglomerados de moléculas de gás de efeito estufa

Abstract

The resulting global climate change due to global warming phenomenon and ozone layer depletion are posing serious challenge to the scientific community as well as to the human society in general. Temperature equilibrium in the Earth’s atmosphere is maintained by a balanced absorption and emission of all the electromagnetic radiation reaching surface of the Earth. Over the last few decades, as a by-product of the rapid industrial and economic growth in several countries, the concentration of the greenhouse gases in the atmosphere is gradually increasing, which, in turn, is increasing the global surface temperature. Carbon dioxide, Methane, nitrous oxide, hydroflurocarbons (HFC), Chloroflurocarbons (CFC) are some of the most commonly known greenhouse gases that are being released to the earth’s atmosphere with ever increasing volume by the worldwide anthropogenic and industrial activities. In this respect, it is important to know the physical characteristics of these greenhouse gases in order to assess scientifically which properties are most important in determining their efficacy and how we can minimize the heat absorption capacity of these molecular species. Keeping in mind the social importance of these facts regarding greenhouse gas (GHG), we have made a detailed analysis of a few electrical and spectral properties of some gases like methane (CH4), Perfluorocarbon (CF4) and some other intermediate fluorocarbons and Chlorofluorocarbons such as CH3F, CH2F2, CHF3, CClF3, CCl2F2 e CCl3F in a micro-solvated environment using high level quantum chemical methods. The ab initio quantum chemical calculations using the second-order Moller-Plesset Perturbation Theory (MP2) and Density Functional Theory (DFT), with sufficiently large basis. Fully unconstrained geometry optimizations and harmonic frequencies are obtained for the hydrogen bonded structures of the greenhouse gases and the solvent molecules using different basis sets. We have calculated the binding energies besides several electrical properties like the dipole moment, mean polarizability, interaction polarizability and polarizability anisotropy for each of these systems and investigated the dependence of the total infra-red absorption intensity of each greenhouse gases on the number of polar bonds and hydrogen bonds. The insights gained by this investigation may help in better understanding the global warming process at a molecular level.