A KINETIC-STUDY OF THE REACTIONS OF FE(A D-5) AND FE-6) WIFH N2O OVERTHE TEMPERATURE-RANGE 294-850 K((A D)

The reaction between Fe and N2O has been studied by the pulsed two-pho ton dissociation at 193 nm of ferrocene vapour to produce Fe atoms in an excess of N2O and N-2 bath gas, followed by time-resolved laser ind uced fluorescence (LIF) spectroscopy of atomic Fe at 248.3 nm [Fe(x(5) F(5)(0)-a D-5(4))]. This yielded k(487 < T/K < 850) = (2.3(-1.0)(+1.8) ) x 10(-10) exp[-(49.4+/-3.0) kJ mol(-1)/ RT] cm(3) molecule(-1) s(-1) , where the quoted uncertainty is 2 sigma. The large activation energy can be explained by the high ionization potential of atomic Fe and th e substantial energy required to promote the valence 4s electron to th e virtual 4p orbital, in accord with the theory of Futerko and Fontijn . The reaction between Fe+ and N2O was studied by the pulsed four-phot on dissociation at 248 nm of ferrocene vapour, producing Fe+ in an exc ess of N2O and He bath gas. The Fe+ ions were then monitored by time-r esolved LIF at 260.0 nm [Fe+(z(6)D(9/2)(0)-a(6)D(9/2))], yielding k(29 4 < T/K < 773) = (5.3(-1.6)(+2.3)) x 10(-10) exp[-(6.2 +/- 1.3) kJ mol (-1)/RT] cm(3) molecule(-1) s(-1). The form of this Arrhenius expressi on can be reconciled with the excitation function measured in an ion-b eam gas experiment if it is assumed that the reaction is activated by vibrational excitation of N2O.