Kinetic study of the reaction of Ru(a 5F5) with N2O and O2 from 296 to 623 K

Abstract

The gas-phase reactivity of Ru(a 5F5) with N2O and O2 in the temperature range 296–623 K is reported. Ruthenium atoms were produced by the photodissociation of ruthenocene and detected by laser-induced fluorescence. The reaction rate of the ground a 5F5 state with N2O is very slow and temperature dependent. The bimolecular rate constant exhibits marked non-Arrhenius behaviour. The rate constants are described by the empirical relation ln(k)=(– 54.4 ± 0.2)+(3.95 ± 0.04)ln T or, alternatively, by the biexponential relation k(T)=(1.3 ± 0.3)× 10–12 exp(– 11.1 ± 0.5 kJ mol–1/RT)+(1.9 ± 1.9)× 10–10 exp(– 37.8 ± 5.7 kJ mol–1/RT) cm3 s–1 where the uncertainties are ±σ. The disappearance rates in the presence of N2O are independent of buffer gas identity (Ar or N2) and total pressure indicating a bimolecular abstraction mechanism. The reaction rate of the a 5F5 state with O2 is pressure dependent and decreases with increasing temperature indicating adduct formation. The limiting low-pressure third-order, k0, and limiting high-pressure second-order, k∞, room-temperature rate constants in argon buffer are (5.2 ± 0.7)× 10–29 cm6 s–1 and (2.8 ± 0.2)× 10–11 cm3 s–1, respectively. In N2, k0 and k∞ are (1.1 ± 0.2)× 10–28 cm6 s–1 and (6.3 ± 0.3)× 10–11 cm3 s–1, respectively. An upper limit of 498 kJ mol–1 is established for the bond energy of RuO(g) based on the lack of a bimolecular reaction for Ru(g) with O2.