Computing molecular complexes in earth's and other atmospheres

Abstract

There has been a considerable research interest in molecular aggregates, complexes or clusters, relevant to Earth's and other planetary atmospheres. Consequently, a considerable amount of data has been obtained in laboratory observations and also in computations. This report surveys our recent and ongoing computations of several such systems of atmospheric significancy, both systems with relatively weak and relatively strong bonding interactions. Among them, several types of homo- and hetero-dimers with importance to Earth's atmosphere: (H2O)2, (N2)2, N2O2, , (O2)2, or (O3)2. Dimer of carbon dioxide (CO2)2 is computed owing to its supposed significancy in the atmosphere of Venus. Systems with stronger bonding are represented by ClONO2H+ and 2,3,7,8-tetrachlorodibenzo-p-dioxin. The report also discusses computational tools, combining advanced quantum-chemical methods with statistical-mechanical treatments. The structure, energetics, and vibrations of the complexes are evaluated at correlated ab initio levels. The computations typically show several minimum-energy structures and their relative populations are sensitive to temperature. The computed dimerization equilibrium constants are of a special interest as a critical stability measure and an input information for evaluations of the altitude population profiles in the atmosphere. A special attention is paid to the temperature enhancement of clustering degree in saturated vapors. This interesting paradox represents a product of atmospheric studies though it is actually a phenomenon of a more general physico-chemical validity.