Oxidative Degradation of Small Cationic Vanadium Clusters by Molecular Oxygen: On the Way from Vn+ (n = 2−5) to VOm+ (m = 1, 2)

Ion-cyclotron resonance mass-spectrometric experiments are used to examine the reactions of small cationic vanadium clusters V n + and vanadium-oxide clusters V n O m + ( n ≤ 5, m ≤ 3) with molecular oxygen. Most of these reactions are very fast (k ≥ 3 × 10 -10 cm 3 molecule -1 s -1 ) and strongly exothermic. Oxidative degradation of the clusters (decreasing n ) is generally more favored than oxygen-transfer resulting in V n O m + cations (constant n ). Consequently, the mononuclear oxide ions VO + and VO 2 + evolve as the major final products at the end of a reaction cascade. For V 2 + and V 3 +, 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 V 2 O m + ( m = 1−3): 920 kJ/mol ≤ Δ f H (V 2 O + ) ≤ 1130 kJ/mol; 670 kJ/mol ≤ Δ f H (V 2 O 2 + ) ≤ 880 kJ/mol, and 420 kJ/mol ≤ Δ f H (V 2 O 3 + ) ≤ 630 kJ/mol.