ROTATIONAL SPECTRA OF SYMMETRIC TOP MOLECULES: CORRELATION-FREE REDUCED FORMS OF HAMILTONIANS, ADVANCES IN MEASURING TECHNIQUES, AND DETERMINATION OF MOLECULAR PARAMETERS FROM EXPERIMENTAL DATA

A theory is discussed in detail of the unitary transformations of the effective rotation and vibration-rotational Hamiltonians of axially symmetric molecules leading to correlation-free reduced forms of these Hamiltonians. Various aspects are discussed of the use of reduced Hamiltonians in fitting the highly accurate data of the rotational and vibration-rotational spectroscopy for the ground as well as excited vibrational molecular states. Advances in measuring techniques in the sub-millimeter-wave spectroscopy and in one-dimensional and two-dimensional microwave Fourier transform spectroscopy are described and their applications are presented on numerous examples of the determination of molecular parameters for the ground and excited vibrational states. The high precision and accuracy of the submillimeter-wave and especially microwave Fourier transform spectroscopy make it possible to verify theoretical conclusions and to use novel approaches like fitting the experimental data with unitary equivalent sets of parameters.