Pure rotational spectrum and model calculations of indole–water

Abstract

The molecular beam Fourier transform microwave spectra of two isotopomers of the 1:1 complex between indole and water have been measured. The water molecule has been reliably located in the complex from these experimental data. The complex has a Cs symmetry with an N–H⋯O hydrogen bond and the plane of the H2O molecule perpendicular to the indole plane. The two-dimensional potential energy surface of the internal rotation and inversion of water in the complex, evaluated with B3LYP/6-31G** or MP2/6-31G** quantum chemical calculations, suggests the tunneling motion of water to take place with the contribute of both motions. The experimental evidence combined with flexible model calculations, indicate, however, that the tunneling motion is mainly an internal rotation of water around its C2 symmetry axis.