Environmental Context. Meteoric ablation profoundly influences the spectroscopic, chemical, and thermal properties of Earth’s upper atmosphere, yet much of the chemical processing of meteor-derived material remains a mystery. As the most abundant main-group metal in meteoric material, magnesium likely plays an important or dominant role but its mesospheric chemistry has received comparatively little study to date.

Abstract. High-level quantum chemical calculations address the structural and thermochemical properties of several novel magnesium-containing molecular ions which, we argue, are relevant to the Mg⁺ chemistry initiated by meteoric ablation in the mesosphere. A model for Mg⁺ chemistry is evaluated, with results indicating that most ionized magnesium at altitudes of 90 km and below is rapidly hydrated due to the association reactions of the pivotal HOMg⁺ ion. The implications of this new mechanism, apparently leading towards noctilucent cloud nucleation by Mg⁺, are briefly explored.