DIOXYGEN COMPLEXES OF 3D TRANSITION-METAL ATOMS - FORMATION REACTIONS IN THE GAS-PHASE

Reactions of ground-state 3d transition-metal atoms including Ti, Mn, Co, Ni, and Cu with molecular oxygen in Ar buffer gas have been investigated in the pressure range 5-700 Torr at 296 K. Attention has been given to termolecular association reactions in which mono(dioxygen) complexes are formed. A pulsed laser photolysis-laser fluorescence technique is used where metal atoms are produced by visible multiphoton dissociation of a volatile organometallic precursor in a static pressure reaction cell, and reactions of metal atoms are monitored by resonance fluorescence excitation at variable time delay following the photolysis pulse. The present study completes a survey of the reactions of 3d transition-metal atoms with O2 under room temperature conditions, from which it emerges that reactivity with respect to complex formation is correlated with a d(n)s1 valence electron configuration of the metal atom. Simplified RRKM calculations have been used to interpret termolecular rate constants for the association reactions in terms of a trend in the binding energies of the dioxygen complexes.