The kinetics and equilibria of clustering reactions (CO)+nminus;1+CO=(CO)+n(n=3ndash;18) were studied, using a pulsed electronhyphen;beam highhyphen;pressure mass spectrometer. It was found that there are two isomers for the tetramer (CO)+4. The energy barrier for the isomerization reaction was measured to be 6.1 kcal/mol. Anomalous vanrsquo;t Hoff plots for the clustering reactions were obtained withn=8ndash;10, probably due to the existence of several isomeric cluster ions. The structures of the cluster ions (CO)+nwithn=2ndash;5 were examined byabinitioMO calculations. Two core ions ofn=3, sgr; and pgr; radical cations, are found to give different clustering patterns.
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