High-resolution molecular spectroscopy provides us with the most detailed information of the structure and properties of molecules. In this seminar, I will give a brief introduction to high-resolution molecular spectroscopy and then focus on one of the molecules that I have been studying, the methoxy radical (CH₃O). In CH₃O, spin and orbital angular momenta of electrons and vibrational motion of nuclei are coupled to each other in the Jahn-Teller and spin-orbit interactions. To decouple these interactions, different spectroscopic techniques - laser-induced fluorescence (LIF), stimulated-emission pumping (SEP), and microwave spectroscopy - are combined to determine the spin-rovibronic (rotational, vibrational and electronic) structure of CH₃O as well as its deuterium isotopomers (CH₂DO, CHD₂O, and CD₃O), which reveals geometry and dynamics of these intriguing molecules. The same spectroscopic techniques have also been applied to molecules with lower or no symmetry. In low-symmetry molecules such as ethoxy (C₂H₅O) and isopropoxy (i-C₃H₇O), the Jahn-Teller effect reduces to pseudo-Jahn-Teller effect. For larger molecules, different isomers and conformers can be identified in high-resolution spectroscopy studies. The obtained and analyzed spectra can be used both as a diagnostic tool in the investigation of chemical kinetics and as a test for quantum chemical calculations.

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