Metal-containing molecules: some new candidates for interstellar detection

High-level ab initio quantum chemical calculations have been employed to in vestigate structural and thermochemical properties of the molecules c-C3HM, MCCCH, MNCCC and MCCCN (M = Na, Mg, Al), which are feasible dissociative r ecombination products of the reactions of M+ with C3H2 and HC2n+1N. A detai led study of the MCCCN and c-C3HM optimized geometries, obtained using vari ous basis sets, has furnished values for the rotational constants of these species to an expected accuracy of +/-2 per cent, which should assist in th eir laboratory or radioastronomical detection. In an examination of the mec hanisms by which these species may arise, we conclude that MgCCCN is the be st candidate for detection within the outer envelopes of carbon-rich AGE st ars such as IRC + 10216; that NaCCCN and AlCCCN may well arise via inner-en velope chemical processes within IRC +/- 10216 (but are unlikely to be foun d 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.