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.