Neutralization‐reionization mass spectrometry (NRMS). Structural information from vertical neutralization and reionization efficiencies

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Abstract
The neutralization‐reionization mass spectra of alkane radical ions indicate significant differences between the structures and geometries of alkane molecules and their molecular ions, confirming recent ab initio predictions. Ionic isomers that are indistinguishable by collisionally‐activated dissociation because of easy interconversion can be characterized by neutralization‐reionization if the corresponding neutrals show different reactivities, as is demonstrated for the [C2H5]+/C2H5˙ system and for [C2H4O2]+˙ isomers. For identification of mixtures of more than one neutral species, the relative efficiency for reionizing each neutral must be determined; e.g. the O2 reionization efficiency of ˙CH2OH radicals is ∼4 times greater than that of CH3O˙. This information and reference reionization spectra of CH3O˙ and ˙CH2OH show that metastable or collisionally activated methyl acetate cations lose CH3O˙, not ˙CH2OH as previously reported; the newly‐formed CH3O˙ undergoes partial (∼20%) isomerization to ˙CH2OH in the ∼10−6s before reionization. Similar results are obtained for [B(OCH3)3]+˙.