Oxidative Degradation of Small Cationic Vanadium Clusters by Molecular Oxygen:  On the Way from V<i>_n</i>⁺ (<i>n</i> = 2−5) to VO<i>_m</i>⁺ (<i>m</i> = 1, 2)

Ion-cyclotron resonance mass-spectrometric experiments are used to examine the reactions of small cationic vanadium clusters Vn+ and vanadium-oxide clusters VnOm+ (n ≤ 5, m ≤ 3) with molecular oxygen. Most of these reactions are very fast (k ≥ 3 × 10-10 cm3 molecule-1 s-1) and strongly exothermic. Oxidative degradation of the clusters (decreasing n) is generally more favored than oxygen-transfer resulting in VnOm+ cations (constant n). Consequently, the mononuclear oxide ions VO+ and VO2+ evolve as the major final products at the end of a reaction cascade. For V2+ and V3+, the complete network of elementary steps is explored by MS/MS experiments. Furthermore, some thermochemical brackets are derived, e.g., for the enthalpies of formation of the ions V2Om+ (m = 1−3): 920 kJ/mol ≤ ΔfH (V2O+) ≤ 1130 kJ/mol; 670 kJ/mol ≤ ΔfH (V2O2+) ≤ 880 kJ/mol, and 420 kJ/mol ≤ ΔfH (V2O3+) ≤ 630 kJ/mol.