Density functional theory and complete basis set ab initio computational study of the molecular interaction between the magnesium atom and nitrogen oxide cation: is the nitrogen oxide cation responsible for higher magnesium cation/atom ratio in the Earth's upper atmosphere?

To facilitate the experimental simulation of the electron transfer reaction between the magnesium atom and the nitric oxide cation complete basis set and density functional theory computational studies were performed to explo re the Mg + NO+ potential energy surface in both its singlet and triplet st ates. In general, two isomers MgNO+ and MgON+ in their singlet and triplet states were located with optimization of their geometries, computation of t he energy of association, and energies of dissociation after the electron t ransfer I reaction had occurred. It was determined that all these isomers w ere very close in energy (around 100 kcal/mol) and therefore they might all be present in same amounts when the magnesium atom is transferred into the magnesium mono-cation. The association energy between the magnesium atom a nd the nitric oxide cation is predicted to be around 50 kcal/mol. On the co ntrary, the enthalpy for the transformation into the magnesium mono-cation and nitric oxide is below 10 kcal/mol and for some Mg-NO+ isomers even less than 2 kcal/mol. The estimated NO stretching harmonic frequencies for all the isomers are quite distant from NO+ and other isomers and should be used for the determination of these isomers in reaction mixtures. Further, thei r IR intensity is very strong and can be used for the estimation of the Mg- NO+ complexes relative energies. (C) 2000 Elsevier Science B.V. All rights reserved.