Guided ion beam studies of the reactions of Crn+ (n=1–18) with CO2: Chromium cluster oxide bond energies

The kinetic energy dependence of the reactions of Crn+ (n=1–18) with CO2 are studied in a guided ion beam mass spectrometer. The primary product ions are CrnO+, which then decompose by sequential loss of chromium atoms as the kinetic energy is increased. Simple collision-induced dissociation to form the Crn−1+ product ions is also observed. Large cluster ions, n⩾9, form the CrnCO2+ adduct at low kinetic energies. For many cluster sizes, the cross section for the primary reaction, Crn++CO2→CrnO++CO, exhibits an interesting bimodal energy behavior that is discussed in some detail. Crn+–O bond energies are measured and found to compare well with measurements obtained from guided ion beam studies of the Crn++O2 systems. The trends in this thermochemistry are discussed and compared to bulk phase oxidation values.