Advancements in Microwave Spectroscopy

About 10 years ago we published two chapters concerning microwave spectroscopy in the first Elsevier book on Frontiers in Molecular Spectroscopy. One of them was concerning the most interesting molecular systems investigated by rotational spectroscopy and the second one the most recent advancements in the related techniques.During the last years, new exciting experiments have been described; probably the most important is the chiral discrimination by double-quantum coherence phase inversion and the diffusion of the chirp techniques.The implementation of "broadband chirp excitation" spectrometers and further development of "single-tone excitation" Fourier transform microwave spectroscopy, most favorably combining with supersonic-jet expansion techniques that make use of various pulse sources, most notably laser ablation sources, allowed for an extensive collection of data.Many of the investigated molecular systems are aimed to solve chemical problems or related to the internal dynamics.A great effort has been devoted to the recording of spectra of species of astrochemical interest, and many new chemical compounds have been observed in the interstellar or circumstellar medium and also comets or planetary atmospheres.A number of interesting examples, achieved in the last 10 years, are compiled here