The Generation and Characterization of Molecules by Neutralization‐Reionization Mass Spectrometry (NRMS). New Analytical Methods (33)

The diluted gas phase within a mass spectrometer is ideally suited for performing collision experiments of fast moving ions with thermalized target atoms. One important reaction which can be brought about with a given cation is its selective reduction, i. e. its neutralization. This allows the synthesis in tailored experiments of a variety of unusual chemical species, which because of intermolecular processes cannot be prepared or studied in solution or in a matrix. Among the molecules which have been generated in this way are hypervalent species (Rydberg radicals) like H   3 ⊙ , van der Waals complexes like He 2 , mono‐ or disubstituted acetylene derivatives XCCY (X H, Y OH, NH 2 ; X Y OH, NH 2 ), and elusive compounds like carbonic acid (H 2 CO 3 ) or carbamic acid (NH 2 CO 2 H). Collision experiments can also be used advantageously for the structural analysis of the neutral molecule N generated in unimolecular dissociation reactions of the type m   1 ⊕→ m   2 ⊕ + N . The dissociation of ionized aniline for example yields, besides C 5 H   6 ⊙⊕cations, neutral isocyanic acid, HNC, and not cyanic acid, HCN. The technique of Neutralization Reionization Mass Spectrometry (NRMS) is performed in the diluted gas phase, a medium where intermolecular interactions are entirely absent. The method may therefore increasingly be applied to the study of molecular species whose reactivity precludes their characterization in matrices. Molecules in specific excited states and fragments of organometallic compounds with unsaturated valencies are two examples of systems which could fruitfully be studied.