Knowledge Bank

Metal ion-acetylene complexes of the general form $M+-(C2H2)n$ are synthesized in the gas phase by a pulsed nozzle laser ablation cluster source. These ions are then mass selected in a reflectron time-of-flight mass spectrometer where they are excited and undergo multiphoton absorption from a tunable infrared OPO/OPA laser system. Efficient fragmentation occurs by the loss of whole $C2H2$ units and this process is enhanced on vibrational resonances near the symmetric and asymmetric C-H stretch frequencies of acetylene. Infrared photofragmentation spectra are obtained by monitoring the fragment yield versus energy of the tunable infrared laser in the $3000cm-1$ to $3400cm-1$ region. the observed infrared band positions are red-shifted from those of free acetylene consistent with the weakening of the carbon-carbon bond energy by $\pi$ electron withdrawal. Interpretation of the spectra for $M+=Ni+$ and $Co+$ will be discussed.