Do the O2 Schumann–Runge Bands Participate in keV Collision-Induced Dissociation Experiments?

In high-energy (keV) CID experiments, oxygen has the unique ability to enhance specific ion fragmentation pathways that lie within a relatively narrow band of activation energy. It has been previously proposed that this oxygen-enhanced dissociation phenomenon is due to the participation of the \( {{\hbox{O}}_{{2}}}\;{\hbox{B}}{\,^{{3}}}{\Sigma_{\rm{u}}}^{ + } - {\hbox{X}}{\,^{{3}}}{\Sigma_{\rm{g}}}^{ - } \) (Schumann–Runge) system in the collision complex. During the collision, oxygen is first excited to its \( {\hbox{B}}{\,^{{3}}}{\Sigma_{\rm{u}}}^{ + } \) state before it returns this energy to the projectile ion. This energy drives the nonstatistical dissociation of the projectile provided there is an energetically accessible pathway in resonance with the absorbed radiation. To probe the validity of this hypothesis, a modified VG-ZAB mass spectrometer was used to observe the photon emissions from keV collisions of a selection of projectile ions with O2 target gas. By studying the resulting collision-induced emission (CIE) spectra, a second potential mechanism came to light, one that involves the near-isoenergetic O2+. A 2Πu→X 2 Πg state transition.