AbstractThe molecular cations of 1,3,5‐cyclooctatriene (COT+·) and bicyclo[4.2.0]octa‐2,4‐diene (BCO+·) can be observed intact in γ‐irradiatedFreonglasses, as opposed to Ar matrices where ionization is accompanied by extensive rearrangements. This proves the superiority of theFreon‐glass method for the generation of metastable primary cations. The electronic absorption (EA) spectra reveala) that a previous analysis of the BCO+·electronic structure on the basis of the ultraviolet photoelectron (UP( spectrum of BCO was incomplete, andb) that COT undergoes planarization upon ionization, in accord with qualitative expectations and MNDO calculations. A previously proposed LCBO model was used to assess the influence of the above geometry change on the electronic struc