Knowledge Bank

Among the members of the vibrational progressions assigned to the four components of the first s Rydberg transitions of methyl $iodide1-3$ are bands assigned to singly excited e ($C3v$ point group) vibrations. Vibronic coupling is assumed responsible for the intensity of these nominally forbidden transitions. Three of the electronic states involved are of e symmetry; therefore, these vibronic interactions result in Jahn-Teller splitting into e, $a1$, and $a2$ component vibronic states. Investigations have been made to determine symmetries of the vibronic transitions and several bands assigned to the $\nu 6$ vibration were found to be $perpendicular4$ We have investigated the magnetic circular dichroism spectrum of methyl iodide in the region of these Rydberg bands (ca. 1700-2000 \AA) in an effort to determine which symmetry component(s) is/are observed in absorption. Results of this study will be presented in light of MCD theory and of a perturbation vibronic-coupling model.