Collisionally induced dissociative ionization of neutral products from unimolecular ion fragmentations. 1—Neutral product structures

Abstract A method is described for the investigation of the structure of neutral products from the unimolecular (metastable) dissociative ionizations of mass selected ions, by means of the collisionally induced dissociative ionization of the neutral species themselves. The neutral species, with kilovolt translational energies, enter a positively charged collision cell situated in the second field free region of a standard ZAB‐2F mass spectrometer. Dissociative ionization of the neutrals results therein from their collisions with He target gas. The resulting ions are analysed by means of the electric sector and the relative ion abundances are shown to be structure characteristic. For such experiments the neutral flux should be c . ≥ 0.5% of the selected precursor ion flux; the collision gas pressure must be insufficient to cause significant precursor ion fragmentation in the field free region preceding the collision cell. It was shown that HNC is generated in the fragmentation of aniline molecular ions, whereas HCN is the neutral product in the dissociative ionizations of pyridine, benzonitrile and benzyl cyanide. The neutral radical [C, H 3 , O˙] formed together with [CH 3 CO] + from ionized methyl acetate has the structure ˙CH 2 OH, but that from the analogous fragmentation of the methyl propanoate molecular ion has the structure CH 3 O˙. Allyl radicals were shown to be generated from [(CH 3 ) 2 CHCH 2 OH] + ˙ together with [CH 3 OH 2 ] + ions.