Vacuum Ultraviolet Fingerprints as a New Way of Disentangling Tropylium/Benzylium Isomers.

The two inseparable companions, tropylium ( Tr + ) and benzylium ( Bz + ), were interrogated by vacuum ultraviolet (VUV) radiation from 4.5 to 7.0 eV in an ion trap. These new fingerprints provide a new means of distinguishing these two intertwined C 7 H 7 + isomers. In particular, the singular spectral signature of Tr + in the VUV consists of a single strong electronic transition at ≈6 eV. To illustrate this diagnostic tool, we shed light on the structure of the C 7 H 7 + intermediate that is ubiquitous when using commercial atmospheric pressure photoionization (APPI) sources. We have identified its structure as the 7-membered ring Tr + , which contradicts some previous beliefs.