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

AbstractThe 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 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.