Among larger systems, a focus in the literature has been on benzene and its radical cation, as well as on their halo (especially fluoro) derivatives. Already in the early 1980s, a wealth of information emerged from the detailed analysis of experimental emission spectra of 1,3,5- trifluoro- and hexafluoro (and chloro) benzene radical cations. The Jahn–Teller effect in the 1,3,5-trifluoro benzene radical cation is discussed in Section 13.4.2 of the textbook by Bunker and Jensen. For the parent benzene cation one has to rely on photoelectron spectra with comparatively lower resolution because this species does not fluoresce (see also section § Spectroscopy and reactivity). Rather detailed ab initio calculations have been carried out which document the JT stabilization energies for the various (four) JT active modes and also quantify the moderate barriers for the JT pseudorotation.