New cluster species of the type (HCN)(m)(NH3)(n)H+ with m up to 4 and n up to 7 alongwith (NH3)(n)H+ 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)(4)H+, (HCN)(1)(NH3)(3)H+ and (HCN)(2) (NH3)(3)H+. 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)(n)H+, decreases monotonically with increasing n, for n > 2. (C) 2003 Elsevier Science B.V. All rights reserved.