EXPERIMENTAL AND THEORETICAL-STUDY OF THE REACTION FE+O-2+N-2-]FEO2+N-2

The recombination reaction between Fe and O-2, has been studied by the pulsed photodissociation at 193.3 nm of ferrocene vapour to produce Fe atoms in an excess of O-2, and N-2, bath gas, followed by time-resolved laser-induced fluorescence spectroscopy of atomic Fe at 248.3 nm [Fe(x F-5(5)0-a D-5(4))]. This yields k(288 < T/K < 592) = (4.34 +/- 0.96) x 10(-30) exp[-(16.94 +/- 0.67) kJ mol(-1)/RT] cm(6) molecule(-2) s(-1), where the quoted uncertainty is 2 sigma. Ab initio quantum calculations on FeO2, indicate that the ground electronic state is a superoxide with an isosceles triangular geometry, FeO2((7)A(1)). The bond energy, D-0(Fe-O-2), is estimated to be 180 +/- 50 kJ mol(-1). These calculations, combined with RRKM theory, demonstrate that the positive temperature dependence of this recombination reaction is caused by barriers in the entrance channels of the manifold of potential-energy surfaces that arise from the interaction of Fe(a D-5(i)) and O-2((3) Sigma(g)(-)). The recommended rate coefficient between 150 and 2000 K is given by log(k/cm6 molecule(-2) s(-1)) = - 161.87 + 119.32x - 36.057x(2) + 3.6303x(3), where x = log(T), and the uncertainty in k is estimated to be +/- 25%. The implications of this result for the chemistry of meteor-ablated Fe in the upper atmosphere are then considered.