15min:

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}\mathrmE_3/2 \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.