HIGH-RESOLUTION LASER-INDUCED FLUORESCENCE SPECTROSCOPY OF CYCLOHEXOXY: ROTATIONAL AND FINE STRUCTURE OF MOLECULES IN NEARLY DEGENERATE ELECTRONIC STATES

Abstract

The previously obtained $\tilde B ^2$A$'-\tilde X ^2$A$''$ and $\tilde B ^2$A$'-\tilde A ^2$A$'$ laser-induced fluorescence (LIF) spectra of jet-cooled cyclohexoxy radical ($c$-C$_6$H$_{11}$O)\footnote{"Jet-cooled laser spectroscopy of the cyclohexoxy radical'', L. Zu, J. Liu, G. Tarczay, P. Dupr\'e, and T. A. Miller, \emph{J. Chem. Phys.} \textbf{120}, 10579 (2004).} have been analyzed and simulated using the coupled-two-state model presented in the preceding talk. The rotational and fine structure of the nearly degenerate $\tilde X ^2$A$''$ and $\tilde A ^2$A$'$ states is reproduced using one set of molecular constants including rotational constants, spin-rotation constants, effective spin-orbit constants ($a \zeta _e d$) and the vibronic energy separation between the two states ($\Delta E$). While the energy level structure could be reproduced by only \emph{effective} spin-rotation constants (without the spin-orbit constant), the spin-orbit interaction introduces transitions that have no intensity using the separate-states asymmetric rotor model. Rotational and fine-structure analysis using the two-state model has proven to be an effective method to separate the first order electron-spin-molecular-rotation constants from the effective spin-rotation constants, and to decouple the spin-orbit splitting ($a \zeta _e d$) and the vibronic energy separation ($\Delta E$), both of which contribute to the experimentally observed energy separation between the two coupled states ($\Delta E ^{\tilde A -\tilde X}$). Isopropoxy (discussed in the preceding talk), cyclohexoxy, and other molecules in nearly degenerate electronic states provide unique cases bridging the gap from symmetrically degenerate states, e.g., ground $\tilde X ^2$E state of methoxy, and the Born-Oppenheimer limit of unperturbed electronic states.