The B2A'-X2A' and B2A'-A2A� laser-induced fluorescence (LIF) spectra of jet-cooled isopropoxy radical (i-C3H7O) have been recorded. The observed rotational and fine structure of the B-X origin band can be well simulated with rotational constants for both the X and B states and the effective electron spin-rotation constants of the X state. The line intensities of the B-X transition are well reproduced using the asymmetric top model, while the rotational contour of the B-A transition deviates from the simulation. The fit values of the effective spin-rotation constants, particularly the large magnitude for ?aa with a-axis perpendicular to the Cs plane, are anomalous, indicating strong coupling between the two near degenerate electronic states, separated by ~60.7(7) cm-1 in energy. The rotational and fine structure of both X and A states can be reproduced in a two-state coupling model that includes the Coriolis interaction, spin-orbit interaction and the vibronic energy separation between the two states (?EA-X). Hamiltonian matrix elements and transition intensities formulae have been derived in both Hund's case (a) and Hund's case (b) basissets. The two-state coupling model has been implemented to simulate previously obtained high-resolution spectra of ethoxy (B2A'-X2A�) and cyclohexoy (B2A'-X2A� and B2A'-A2A'), with A-X separation of ~364 cm-1 and ~62 cm-1, respectively. Rotational and fine-structure analysis using this model has proven to be an effective method to decouple the spin-orbit splitting (a?ed) and the vibronic energy separation (?E), both of which contribute to the experimentally observed energy separation between the two coupled states. The studied free radicals in their nearly degenerate electronic states provide unique cases bridging the gap from symmetrically degenerate states, e.g., ground X2E state of methoxy, and the Born-Oppenheimer limit of unperturbed electronic states.

High-resolution laser-induced fluorescence spectroscopy of ethoxy, isopropoxy and cyclohexoxy: Rotational and fine structure of molecules in nearly degenerate electronic states

246th National Meeting (2013)

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