The behavior of oxygen as a collision-induced dissociation target gas

The unusual and unique ability of O 2 as target gas in kV collision-induced dissociations, to enhance a specific fragmentation of a mass selected ion, has been examined in detail. The affected dissociations studied were the loss of CH 3 · from CH 3CH +X (X = OH, CH 3, NH 2, SH); CH 3 · and Cl · loss from CH 3C +(Cl)CH 3; C 2H 5 · loss from CH 3CH 2CH +X (X = OH and NH 2); H · loss from +CH 2OH and +CH 2NH 2; O · loss from 1,2-, 1,3-, and 1,4-C 6H 4(NO 2) 2 +·; CH 3NO 2 +·; C 6H 5NO 2 +·; C 5H 5NO +· (pyridine N-oxide); 3- and 4-CH 3C 5H 4NO +·. A general explanation of the phenomena, which was semiquantitatively tested in the present work, can be summarized as follows: the ion – O 2 encounter excites the target molecules to their 3Σ g − state which resonantly return this energy to electronic state(s) in the ion. The excited ion now contains a sharp excess of a narrow range of internal energies, thus significantly and only enhancing fragmentations whose activation energies lie within this small energy manifold.