Ilyushin V. Radiospectroscopy of nonrigid molecules in millimeter and submillimeter wave ranges.

Object of investigation: nonrigid molecules with intramolecular large amplitude motions and their rotational spectra. Purpose of investigation: development of theoretical approaches to the description of rotational spectra of nonrigid molecules. Methods of investigation: experimental methods of radiospectroscopy, method of effective Hamiltonian built on the basis of analysis of molecular symmetry group. Theoretical and practical results, novelty: In the dissertation work a substantial progress was achieved for the actual scientific direction of high-precision investigation of rotational spectra of non-rigid molecules complicated with tunneling splittings. The new as well as existing methods of theoretical and numerical analysis of molecular rotational spectra which have substantial complication due to high level of molecular nonrigidity and presence of intramolecular large amplitude motions have been developed and improved. The cases of molecules with torsion vibration of a C3v group attached to the molecular frames of Cs and C2v symmetries are considered as well as the cases of molecules of C2v symmetry with torsion motions of two equivalent C3v groups, and molecules with a combination of torsion vibration of C3v group with vibration of inversion type. In the framework of testing of the developed models the experimental and theoretical investigation of the spectra of the following molecules have been carried out: CH3COOH, CH3CONH2, CH3NH2, HCOOCH3, (CH3)2CO, H2NC(O)OCH3, CH3CCCOOH, CH3C3H2(O)OH, CH3C7H4(O)OH, CH3OH-H2CO, CH3OH-C2O, CH3C6H5, CF3C6H5, CH3CHO. For these molecules a vast amount of new high precision experimental data has been obtained using methods of radiospectroscopy. The results of laboratory investigations of rotational spectra of CH3CONH2 and HCOO13CH3 molecules gave an opportunity to detect these species in interstellar medium.