Main group metal ion chemistry in cold interstellar and circumstellar environments

High-level ab initio calculations, using the CP-dG2thaw method and related approaches, are combined with VTST computations of radiative association rate coefficients to explore the reactivity of atomic metal ions and metal-containing molecular ions with abundant interstellar and circumstellar neutrals. Consequences of the calculated energetics and kinetics of the metal ion / ligand chemistry are surveyed with particular reference to the refractory metals Mg and Ca. The likely composition of the metal-containing populations and the accompanying formation of neutral species like MNC, MCN and MC3N are examined for three different C-rich environments, typified by the cold dark interstellar cloud TMC-1, the outer circumstellar envelope of the AGB star IRC+10216 and the post-AGB object CRL 618, and are discussed with reference to molecular detections within these three objects.