M. Helmer et Jmc. Plane, EXPERIMENTAL AND THEORETICAL-STUDY OF THE REACTION FE-2+N-2-]FEO2+N-2(O), Journal of the Chemical Society. Faraday transactions, 90(3), 1994, pp. 395-401
Citations number
57
Categorie Soggetti
Chemistry Physical","Physics, Atomic, Molecular & Chemical
The recombination reaction between Fe and O-2, has been studied by the
pulsed photodissociation at 193.3 nm of ferrocene vapour to produce F
e atoms in an excess of O-2, and N-2, bath gas, followed by time-resol
ved 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 calc
ulations on FeO2, indicate that the ground electronic state is a super
oxide with an isosceles triangular geometry, FeO2((7)A(1)). The bond e
nergy, D-0(Fe-O-2), is estimated to be 180 +/- 50 kJ mol(-1). These ca
lculations, combined with RRKM theory, demonstrate that the positive t
emperature dependence of this recombination reaction is caused by barr
iers in the entrance channels of the manifold of potential-energy surf
aces 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 gi
ven 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 m
eteor-ablated Fe in the upper atmosphere are then considered.