Structure and intermolecular vibrations of 7-azaindole-water 2:1 complex in a supersonic jet expansion: laser-induced fluorescence spectroscopy and quantum chemistry calculation

Abstract

Laser-induced fluorescence spectra of a 2:1 complex between 7-azaindole and water, known as ‘non-reactive dimer’ of the molecule, have been measured in a supersonic jet expansion. The dispersed fluorescence spectrum of the electronic origin band of the complex shows a very large number of low-frequency vibrational features corresponding to different intermolecular modes of the complex in the ground electronic state. Geometries of several possible isomeric structures of the complex and their vibrational frequencies at harmonic approximation were calculated by electronic structure theory method at MP2/6-31G** level. An excellent agreement is observed between the measured and calculated intermolecular vibrational mode frequencies for the energetically most favoured structure of the complex, where the water molecule is inserted within one of the two N⋯H–N hydrogen bonds of the 7AI dimer.