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 CH3. from CH3CH+X (X = OH, CH3, NH2, SH); CH3. and Cl-. loss from CH3C+(Cl)CH3; C2H5. loss from CH3CH2CH+X (X = OH and NH2); H-. loss from +CH2OH and +CH2NH2; O-. loss from 1,2-, 1,3-, and 1,4-C6H4(NO2)(2)(+.); CH3NO2+. C6N5NO2+.; C5H5NO+. (pyridine N-oxide); 3- and 4-CH3C5H4NO+.. 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 (3)Sigma (-)(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. (C) 2001 American Society for Mass Spectrometry.