Multichannel quantum defect treatment of the Rydberg states of CH3I

An analysis of the observed electronic structure of the high-resolution absorption spectrum of CH3I is presented for the energy regions above and below the first ionization limit. We show that the electronic effects of spin--orbit coupling and l mixing for Rydberg states built on a doublet ion core account for nearly all major features of the spectrum. The present results substantiate a recent ab initio calculation of the electronic multichannel quantum defect theory (MQDT) parameters for HI [H. Lefebvre-Brion, A. Guisti-Suzor, and G. Raseev, J. Chem. Phys. 83, 1557 (1985)]; they also illustrate an important feature of MQDT, namely, the ability to extrapolate channel mixing across threshold from the autoionization region into the discrete region