Interstellar synthesis of the cyanopolynes and related molecules

The cyanopolyynes HC2CN, HC4CN, HC6CN, and HC8CN, and the molecules CH3CHCN and CH3CH2CN, have recently been detected in the interstellar medium. We show that the observed abundances of these molecules can be obtained by gas-phase formation pathways if the reaction of H2CN+ with C2H2 is rapid at low interstellar temperatures. The molecules CH2CHCN and C3N may be formed also by the reactions of H2CN+ with C2H2, and CH3CH2CN may be formed by reaction of H2CN+ with C2H4