MOLECULAR RYDBERG TRANSITIONS. MULTI-CHANNEL APPROACHES TO ELECTRONIC STATES: $CH_{3}I$

We have previously presented a single-channel quantum defect theory (QDT) analysis of the Rydberg states of $CH_{3}I$, up to the $^{2}E_{1/2}$ ionization limit [1]. The purpose of the present paper is to extend our earlier analysis to incorporate multi-channel effects. Feasibility of a multi-channel QDI treatment of molecular Rydberg states is dependent upon the existence of high-resolution VUV data. We have recently published [2] such a spectrum for $CH_{3}I$ (3m vacuum spectrograph, University of Bonn Synchrotrom source, $\\pm 0.003$ {\\AA} resolutions). Our QDT analysis of this data follows the Lu-Fano [3] graphical method. Among our results are the following: --- We have identified a new $CH_{3}I$ d-series converging on the $^{2}E_{3/2}$ ionization limit. --- We have provided a consistent Lu-Fano plot of effective quantum numbers for $CH_{3}I$. Indeed, construction of this plot led to the new assignment mentioned above and vindicates the multi-channel approach for molecular Rydberg states. --- We find a striking similarity in the Rydberg Structures of Xe [4] and $CH_{3}I$ which serves as a confirmation of those similarities discussed in [1].