We describe a three-wave mixing experiment using time-separated microwave pulses to detect the enantiomer-specific emission signal of the chiral molecule using Fourier transform microwave (FTMW) spectroscopy. A chirped-pulse FTMW spectrometer operating in the 2-8 GHz frequency range is used to determine the heavy-atom substitution structure of solketal (2,2-dimethyl-1,3-dioxolan-4-yl-methanol) through analysis of the singly substituted (13)C and (18)O isotopologue rotational spectra in natural abundance. A second set of microwave horn antennas is added to the instrument design to permit three-wave mixing experiments where an enantiomer-specific phase of the signal is observed. Using samples of R-, S-, and racemic solketal, the properties of the three-wave mixing experiment are presented, including the measurement of the corresponding nutation curves to demonstrate the optimal pulse sequence.

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The peculiar propensity of water to have a high internal dynamic activity in its molecular complexes with organic molecules is described in this paper. Often, the corresponding large amplitude motions are reflected in the tunnelling splittings of the rotational transitions which, in turn, provide information for the determination of the potential energy surfaces and of the noncovalent interactions of water with a variety of atoms and/or functional groups. A classification of this kind of molecular complexes is given, also in relation to the tunnelling features of the rotational spectra. As a specific example, the rotational spectrum of tert-butylalcohol-water, investigated by Fourier transform microwave spectroscopy, is reported. Details are given of the large amplitude motions which take place in the adduct, the internal rotation of the hydroxyl group and the oscillations of the water molecule, by interpreting the experimental data with a flexible model.