The covalently bound HCN dimer ions HCN−NCH+ and HCN−C(N)H+ are stable species in the gas-phase, but the neutral counterparts are not

Mass spectrometric experiments and model chemistry calculations (CBS-QB3/APNO) show that the HCN dimer ions HNCCNH+ and HCN-C(N)H+ are stable species connected by a low interconversion barrier.