Mg +NO and Mg +ON: potentially important ionospheric species

Abstract

In order to determine the lowest energy isomer of the Mg + − NO complex, self-consistent field (SCF), configuration interaction including all single and double excitations (CISD), coupled cluster singles and doubles (CCSD), and CCSD with perturbatively evaluated triples [CCSD(T)] ab initio electronic structure methods were employed. Equilibrium geometries, relative energies, dipole moments, harmonic vibrational frequencies, and associated infrared (IR) intensities for the lowest triplet and closed-shell singlet structures were determined. At the CCSD(T) level with the largest basis set, triple-ζ plus double polarization augmented with one set of higher angular momentum and one set of diffuse functions (TZ2PF + diff), the global minimum was predicted to be closed shell, 1 A′ Mg +NO with equilibrium geometry r e (Mg − N) = 2.378 Å, r e (N − O) = 1.147 Å, and θ e = 122.6°. At this same level of theory, 1 A′ Mg +NO was predicted to lie approximately 14 kcal mol −1 below the Mg + + NO dissociation asymptote. At levels of theory below CCSD(T), the 3Π state of Mg +NO is erroneously predicted to be the ground state. The dipole moment with respect to the center of mass is predicted to be 4.9 debyes for the 1 A′ ground state of Mg +NO.