COMPUTATIONAL STUDIES OF ATMOSPHERIC CHEMISTRY SPECIES .10. A COMPUTATIONAL EVALUATION OF POPULATIONS OF COMPLEXES UNDER ATMOSPHERIC CONDITIONS - THE (H2O)2 AND (CO2)2 CASES

Various van-der-Waals or hydrogen-bonded complexes have been understoo d as significant components of the Earth's or other planetary atmosphe res. The species can be characterized by computational-chemistry techn iques. Present possibilities are illustrated with the water dimer desc ribed by flexible potentials. It is shown that the dimer mole fraction in equilibrium with the monomer should be about 0.1-0.2% close to the Earth's surface under saturation conditions. For sample atmospheric c onditions about 3 km above the surface the mole fraction decreases to some 0.004-0.005%. Another example is supplied with the carbon dioxide dimer in the Venus atmosphere, using the Stogryn-Hirschfelder treatme nt within a Lennard-Jones scheme and calculations based on recent quan tum chemical data. The dimer mole fraction in equilibrium with carbon dioxide can be higher than 4% close to the Venus surface and the fract ion should decrease with distance from the surface.