Mass Spectrometric Observations on Reactions of Excited Ions

Reactions have been observed between excited ions of carbon disulfide and carbon disulfide, water, iodine and ethylene. The ions CS3\ C,S,+, C2S3\ H2OS+, CSI+, SI+, C2H : iS+ and C2H4S+ are formed in these reactions. An additional contribution to the C2S2+ ion results from reaction of CS+ with CS2 • The reaction of I2+ with CS2 leads to the ion CS2I+. Reactions of excited molecular ions have also been found in benzonitrile, chlorobenzene, bromobenzene and iodobenzene. Ions of the C12 series such as C12H9CN+, C12H10+ and C12Ha+ are formed in these processes. In all cases, the appearance potential of the secondary ion is lower than the first dissociation limit of the molecular ion. It is therefore concluded that the excited ions are stable towards unimolecular decomposition. Repeller field studies show that they must be metastable towards decay by photon emission. In the case of aromatic ions this is explained by fast internal conversion of electronically excited ions into high vibrational levels of their electronic ground states. The form of the ionization efficiency curves of the secondary ions at high electron energies corresponds to what is expected if the excited precursors are formed in optically allowed transitions.