Internal rotation in symmetric top molecules

Abstract Internal rotation in symmetric top molecules offers an excellent opportunity to investigate large amplitude motion in a relatively simple intramolecular environment. Due to specific symmetry characteristics of a symmetric top molecular frame, the internal rotation degree of freedom is in the zeroth order approximation separable from the small amplitude vibrations and the overall rotation, thus enabling to characterize the vibrational-torsional-rotational energy structure with a relatively simple Hamiltonian. Lessons from symmetric internal rotor studies may be applied to more complex systems, such as asymmetric internal rotors and macromolecules. This thesis deals with internal rotation in CH3SiH3, CH3SiD3, CH3CF3 which have become a prototype of symmetric internal rotors. The thesis presents high resolution vibration-torsion-rotation spectra and detailed analysis of these molecules. Particular attention is focused on torsion-mediated interactions, such as Coriolis-type interactions and Fermi-type interactions, coupling the internal rotation and the small amplitude vibrational motion. The studies show that the expansion of the data to the small amplitude vibrations and inclusion of the torsion-mediated interactions play a crucial role in order to obtain an appropriate characterization of the vibrational-torsional-rotational energy level structure and physically meaningful molecular parameters