BÉRENGER GANS, MONIKA GRÜTTER AND FRÉDÉRIC MERKT, Laboratorium für Physikalische Chemie, ETH Zürich, CH-8093 Zürich, Switzerland.
PFI-ZEKE photoelectron spectra of the \mathrmX+ 2 \mathrmX 1 + transition of HC2I and of the \mathrmX+ 2\mathrmE3/2 \mathrmX 1\mathrmA1 transition of CH3I have been recorded at a resolution sufficiently high to observe, at least partially, their rotational structure. The spin-rovibronic energy-level structures of HC2I+ and CH3I+ could be determined at low energies and enabled us to study the Renner-Teller and Jahn-Teller effects in molecular cations subject to a very large spin-orbit coupling with unprecedented details.
In the case of HC2I, the nominally forbidden 510 band has been observed in addition to the origin band and allowed us to determine a splitting of 2~cm-1 between the two Renner-Teller components of the 51 vibrational level of the cation. In the case of CH3I, the rotational structure of the origin and of the 210 and 310 bands are dominated by satellite bands of spin-rovibronic origin. The 510 and 610 bands reveal an additional splitting corresponding to the separation between the two Jahn-Teller components of j=1/2 and j=3/2 symmetry of the 51 and 61 levels of the cation.