An estimation of the concentration of atmospheric nitrous oxide containing complexes

Abstract

Nitrous oxide (N₂O) is one of the major greenhouse gases responsible for climate change. It also has impacts on the removal of ozone (O₃) from the atmosphere and is now the single most important ozone depleting substance. Atmospheric N₂O primarily comes from bacterial denitrification processes in soils, a process which is augmented by many agricultural practices. As a result of the large amount of agricultural land in New Zealand, emissions of N₂O are disproportionately high for our population. Nitrous oxide is primarily removed from the atmosphere via a photodissociation process, involving photons between 180 - 230 nm. The process of photodisociation involves the bending of the linear structure of the N₂O molecule, which allows for photodisociation to proceed. The presence of other gas molecules, such as those that we are investigating in our complexes, peturbs the bending mode of N₂O, which is throught to alter the photodisociation rate. In this work we investigate the weakly bound complexes of N₂O with the major atmospheric molecules, namely N₂, O₂, Ar and H₂O. We use explicitly correlated coupled cluster theory to determine interaction energy, vibrational frequencies and rotational constants of the four complexes. This data is then used in combination with the standard statistical mechanics equations to determine the equilibrium constant of formation for each complex as a function of altitude. Finally the abundance profile of each complex is determined using the atmospheric concentrations of the constituent monomers.