Ab initio MO caIcuiations were performed for compIeses between HCI and NH3, CH3NHz, (CH3&NH and (CHJ)$X. SCF geometry optimization for the latter three complcscs gives doubte-minimum potential surfaces, which bccomc singtcminimum surfaces wlm~ electron correlation is considered. It is proposed that (CHa)aN-HCI may be an ion pair in the gas phase. I. Inrroducrion Hydrogen-bonded complexes AH . ..B may exist in two possible forms in which the proton is either bound to molecule A (molecular hydrogen-bond form) or to molecule B (ion-pair form). They are related by the proton transfer process: AH...B=A-...HB+. Alternatively there may be a structure, an intermediate form, in which the proton is only partially transferred and shared by A and B. Many experimentat data obtained for hydrogenbonded complexes in solution. as well as in solids. indicate that proton transfer can take place [ I] _ Though rapid progress has been made in the last few years in esperimcntal studies of hydrogen-bonded systems in the gas phase [2.3]. most have dealt with complexes of \veak or medium interaction where the possibility of the existence of an ion-pair form is very small. Very good candidates for ionic pair or intermediate complexes are strong hydrogen-bonded complexes formed by ammonia or siiphatic amines and the hydrogen halides fHC1. HBr or HI).