The mechanism of formation of hydrates of chiral (S) 1,2,3,4-tetrahydro-3-isoquinoline (THIQM) with two water molecules has been investigated in jet-cooled condition by means of resonance-enhanced two-photon ionization and IR–UV double resonance experiments. Quantum chemical calculations reveal that only one isomer of the THIQM is involved in the THIQM-(H2O)2 complex formation, in contrast with what was observed for THIQM-(H2O). Anharmonic vibration calculations allowed unambiguous assignment of THIQM-(H2O)2 to a complex resulting from the addition of a water molecule on the most stable THIQM-(H2O) complex. A sequential mechanism for complex formation has been deduced from these results.
