1. Assignment of transitions from high resolution IR spectra of molecules of large amplitude motions (LAM).
The spectrum analysis is based on the coupled vibration-rotation Hamiltonian which can take account of the Coriolis, Fermi, etc. perturbations. The investigated molecules have been methyl amine and formamide. In the case of methyl amine periodic K quantum number dependences were observed for the upper wagging levels which are perturbed by the second overtone levels of internal rotation. An extremely high resonance and some smaller resonances were found in the spectrum of formamide caused by Coriolis and Fermi couplings. The resolution of IR spectra was 0.001- 0.002 cm-1. MW and MWW data have been also used for the analysis.
2. Treatment of hindered LAM motions for methyl amine.
The treatment of hindered LAM molecules requires elaboration of special theoretical models and programs. The goal is the determination of the potential surface from experimental spectrum data which requires the knowledge of the flexible geometry surface of the molecule. It is not possible to determine simultaneously both surfaces. The resolution of the problem is a combination of the high resolution spectra with the geometry surface calculated by quantum chemical methods. The procedure was applied to methyl amine. Unfortunately the potential surface determined by this way shows some dependence from the applied quantum chemical method and basis set.