Neutralization-Reionization Mass Spectrometry (NRMS). Structural Information from Vertical Neutralization and Reionization Efficiencies

摘要

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 oxygen reionization efficiency of CH2OH radicals is approx. 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 (approx. 20%) isomerization to CH2OH in the approx. .00001 before reionization. Similar results are obtained for (B(OCH3)+.