PRESENT STATE OF SUBMILLIMETERWAVE SPECTROSCOPY AT THE NIZHNII-NOVGOROD LABORATORY

A review of recent developments in microwave spectroscopy techniques i n the Terahertz range and some examples of molecular spectra achieved at the Nizhnii Novogorod Microwave Spectroscopy Laboratory are present ed. Techniques and methodics developed include: development (jointly w ith the KVARZ Institute of Electronic Measurements, Nizhnii, Novogorod ) of a unique series of commercial frequency synthesizers covering the 53-178 GHz range, which are now used in several Western Laboratories; development of laboratory versions of synthesizers up to frequencies exceeding 500 GHz; development (jointly with the Physical Institute of the University of Cologne, Germany) of precise microwave broadband sc anning spectrometers covering a range exceeding 1 THz; development of alternative (non-synthesizer based) techniques of microwave spectrosco py in the submillimeter range; extension of the range of microwave spe ctroscopy up to 1.5 THz by multipication of frequency of the submillim eter backward wave oscillators. New objects of submillimeter microwave spectroscopic studies include: spectra of molecular complexes in equi librium and in supersonic jets; spectra of some light molecules; studi es of effects connected with high excitation of vib-rot states: cluste ring of energy livels in asymmetric tops: development of new methods f or describing the spectra of non-rigid molecules and their application s.Further studies of molecular interactions (pressure line shifts and broadenings) include: achievement of new measurement accuracy limits; study of the shape of strongly shifted lines; studies of the temperatu re dependence of shift and broadening and its applications; study of s ome new effects: experimental demonstration of the existence of non-ad ditivity of pressure lineshifts in the system of molecular transitions ; experimental demonstration of the absence of non-additivity of press ure lineshifts in mixtures of gases. The studies of molecular spectra and molecular interactions were carried out, in part, jointly with the University of Cologne, University of Giessen, Kiel University, Wupper tal University, Molecular Physics Division of the National Institute o f Standards and Technology, and London University. Some perspectives f or the development of submillimeter microwave spectroscopy techniques discussed in this paper include: further extension of the range of mic rowave spectroscopy well beyond 1.5 THz; extension of the range of fre quency synthesizers; some non-spectroscopical applications of the tech niques and methods developed.