Photoionization mass spectrometry

Dissociative Photoionization of the C7H8 Isomers Cycloheptatriene and Toluene: Looking at Two Sides of the Same Coin Simultaneously

“…Because of their ubiquity in the mass spectra of aromatic compounds, the decomposition of gaseous C 7 H 8 + ions is one of the most widely studied ion reactions. These investigations were carried out by techniques including, but not limited to, collisional activation, , photoionization, − ion cyclotron resonance mass spectrometry, − infrared spectroscopy, , and photoelectron photoion coincidence spectroscopy (PEPICO). − Hydrogen abstraction from C 7 H 8 +• ions leads to the formation of C 7 H 7 + cations with more than 30 different possible isomeric structures, with benzyl (Bz + ), tropylium (Tr + ), and tolyl (Tl + ) being the most important ones among them. One of these, Tr + , has received special attention since Hückel predicted it to be a stable seven-membered ring with high aromaticity in 1931 .…”

“…was studied first (see Figure3), which is the first isomerization step connecting the Tol cation to the most stable Tr + fragment ion. The mechanism for(Tol ) [1] → CHT +• [7] → Tr + [9] + H begins with a H migration from the CH 3 -carbon via a tight TS [2] ‡ at 1.66 eV relative to Tol +•[1] and leads to the first intermediate[3] at 1.49 eV. Two more lower lying saddle points,[4] ‡ and [6] ‡ , were located on the PES along with one intermediate structure,[5], leading to ring expansion and CHT +•[7] formation at 0.80 eV.…”