New cluster species of the type (HCN)m(NH3)nH+ with m up to 4 and n up to 7 alongwith (NH3)nH+ species are observed using mass spectrometry, on the reaction of carbon vapor with jet-cooled NH3 in admixture with helium. The most preponderant species correspond to m=1 and 2, viz. (HCN)1(NH3)4H+, (HCN)1(NH3)3H+ and (HCN)2(NH3)3H+. These clusters involving the tetrahedral coordination in the first solvation shell of the NH4+ ion are the most stable species, as corroborated by molecular-orbital calculations. The incremental complexation energy due to successive addition of the NH3 molecule to (HCN)(NH3)nH+, decreases monotonically with increasing n, for n 2. © 2003 Elsevier Science B.V. All rights reserved.