The production of HCN dimer and more complex oligomers in dense interstellar clouds

Using quantum chemical and kinetic techniques, we show that the reaction between two HCN molecules under interstellar conditions cannot lead efficiently to a dimer of this species (H2C2N2), whatever its structure. If the dimerization reaction does not occur efficiently, then it is impossible to synthesize detectable abundances of the pre-biotic HCN oligomer adenine (H5C5N5) in the interstellar medium via successive neutral-neutral reactions between HCN and its dimer, trimer, and tetramer.