ISSN 1017-2548(Print)
ISSN 2234-8530(Online)
Volume 53, Number 2
JKCSEZ 53(2)
April 20, 2009 

We present calculations for the 4-aminopyrimidine (4AP) - HCl and -HBr complexes. We predict that the charge separated (zwitterionic) form [4APH⁺ - Cl^-] is not stable, but that [4APH⁺ - Br^-] is stable enough for experimental detection in gas phase at low temperatures. The latter observation is attributed to smaller dissociation energy of HBr compared with HCl, and to “solvation” of HBr by the amino group in 4AP.