Ionization and protonation of (MgCN): an ab initio study of some gas-phase properties of the first magnesium compound in space

Abstract

An ab initio study of the ionized and protonated derivatives of the (MgCN) system, the first magnesium-containing molecule detected by radioastronomers, has been carried out. For the (MgCN) + system we have found a cyclic ground state, lying below linear MgCN + and MgNC + by only 1.8 kcal mol −1 and 3.0 kcal mol −1, respectively, at correlated levels of theory. The estimated ionization potentials for both MgNC and MgCN are relatively small, 7.93eV and 7.72eV, respectively. The preferred protonation sites are carbon for MgNC and nitrogen for MgCN, with very high proton affinities of more than 220 kcal mol −1 for both MgNC and MgCN. Enthalpies for some of the possible ion-molecule reactions which could produce precursors of (MgCN) in space have also been computed. It is found that only the reaction of MgH + with hydrogen isocyanide to produce (MgCN) + is clearly exothermic.