Metal-containing molecules: some new candidates for interstellar detection

High-level ab initio quantum chemical calculations have been employed to investigate structural and thermochemical properties of the molecules c-C3HM, MCCCH, MNCCC and MCCCN (M = Na, Mg, Al), which are feasible dissociative recombination products of the reactions of M+ with C3H2 and HC2n+1N. A detailed study of the MCCCN and c-C3HM optimized geometries, obtained using various basis sets, has furnished values for the rotational constants of these species to an expected accuracy of ± 2 per cent, which should assist in their laboratory or radioastronomical detection. In an examination of the mechanisms by which these species may arise, we conclude that MgCCCN is the best candidate for detection within the outer envelopes of carbon-rich AGB stars such as IRC+10216; that NaCCCN and AlCCCN may well arise via inner-envelope chemical processes within IRC+10216 (but are unlikely to be found within the outer envelope); and that the MC3H structures, particularly c-C3HMg, are worthwhile candidates for a radioastronomical search within cold dense clouds such as TMC-1.