In this part, we are focusing on the fundamental importance of non-covalent interactions in nature by illustrating molecular complexes from chemistry,  physics and the biosciences. High resolution microwave spectroscopy combined with pulse jet technique is used for the study of non-covalent interactions in different kinds of molecular clusters are briefly outlined. The roles of structure and geometry, stabilization energy, internal dynamics for molecular clusters are extensively discussed.

The knowledge of conformational behaviors and geometries is essential to understand, from the molecular level, the change of their physicochemical characteristics and biological activity upon halogenation. High resolution rotational spectra of certain series of flexible molecules are proposed to be investigated using pulse-jet Fourier transform microwave spectroscopic technique combining with theoretical calculation. Precise information on their shapes, geometries, conformational equilibria and internal dynamics will be obtained. Furthermore, it would shed light on the nature and discipline of the factors impacting molecular conformational behaviours, which will be very helpful to tune, more rationally, the organic compounds.

The presence of interstellar molecules would provide the important information for the revolution of interstellar gas and stars.By mimicking the environment of interstellar space with low molecular density in the laboratory, the potential astronomical molecules will be produced on line via the collision under the DC discharge. With pulse jet-Fourier transform microwavespectroscopic technique, the high resolution rotational spectra of potential interstellar molecules will be investigated. The typical pattern of their rotational spectra will be identified. The obtained precise spectroscopic and structural parameters, and the deduced mechanics upon formation are essential to their observation in the interstellar space.