Tunable photoionization chemical monitoring (TPI‐CM)—A means to probe molecular ion structures and monitor unimolecular processes through bimolecular ion–molecule reactions: Past, present, and future

Abstract

The way in which molecules can arrange themselves is at the root of organic chemistry and elucidating the structures present in isomeric mixtures remains a major challenge nowadays. A tantalizing question for chemists is how molecules transform from one structural configuration to another one. This review introduces in details a technique—tunable photoionization chemical monitoring—that couples tandem mass spectrometry and photoionization enabling to answer the two aforementioned questions for molecular ions. It is based on tracking reactivity changes in bimolecular ion–molecule reactions as a function of the internal energy of the ions. This is illustrated with (i) the structural elucidation of ortho‐benzyne distonic cation within a C 6H4+ population and (ii) the tracking of the isomerization from azulene radical cation as it gets gradually energized to naphthalene cation. In both cases, charge transfer reactions have been primarily used because of their universality. Finally, a state‐of‐the‐art of the TPI‐CM technique using the CERISES mass spectrometer is given, indicating current limitations as well as prospects of improvement.

New light on the imbroglio surrounding the C8H+6 isomers formed from ionized azulene and naphthalene using ion–molecule reactions

“…A more detailed discussion of this effect can be found in ref. 31 . It is known that the Franck–Condon factor of the photoionizing origin band of PA is very strong as can be seen in the sharp threshold behavior of PA + ion in Fig.…”

“…The present study focuses on the reactivity of C 8 H + 6 structures with allene and propyne, where the C 8 H + 6 structures are generated either by direct photoionization of phenylacetylene (PA) or dissociative photoionization of Naph and Azu molecules. We employ the tunable photoionization chemical monitoring technique, 31 an approach that has been successful in elucidating the structures of ionic fragments from dissociative ionization 32 and uncovering isomerization pathways. 33 The data set obtained from the current study provides chemical reference for one of the expected C 8 H + 6 species, specifically PA + , facilitating the data interpretation from dissociative ionization of C 10 H 8 species.…”