Cumulenic and heterocumulenic anions: potential interstellar species?

A recent theoretical investigation by Terzieva & Herbst of linear carbon ch ains, C-n where n greater than or equal to 6, in the interstellar medium ha s shown that these species can undergo efficient radiative association to f orm the corresponding anions. An experimental study by Barckholtz, Snow & B ierbaum of these anions has demonstrated that they do not react efficiently with molecular hydrogen, leading to the possibility of detectable abundanc es of cumulene-type anions in dense interstellar and circumstellar environm ents. Here we present a series of electronic structure calculations which e xamine possible anionic candidates for detection in these media, namely the anion analogues of the previously identified interstellar cumulenes CnH an d Cn-1CH2 and heterocumulenes CnO (where n = 2-10). The extraordinary elect ron affinities calculated for these molecules suggest that efficient radiat ive electron attachment could occur, and the large dipole moments of these simple (generally) linear molecules point to the possibility of detection b y radio astronomy.