Kinetic study of the reaction of Ru(a F-5(5)) with N2O and O-2 from 296 to 623 K

The gas-phase reactivity of Ru(a F-5(5)) with N2O and O-2 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 F-5(5) 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) x 10-(12) exp(-11.1 +/- 0.5 kJ mol(-1)/RT) + (1.9 +/- 1.9) x 10(-10) exp(-37.8 +/- 5.7 kJ mol(-1)/RT) cm(3) s(-1) where the uncertainties are +/-sigma. The disappearance rates in the presence of N2O are independent of buffer gas identity (Ar or N-2) and total pressure indicating a bimolecular abstraction mechanism. The reaction rate of the a F-5(5) state with O-2 is pressure dependent and decreases with increasing temperature indicating adduct formation. The limiting low-pressure third-order, k(0), and limiting high-pressure second-order, k(infinity), room-temperature rate constants in argon buffer are (5.2 +/- 0.7) x 10(-29) cm(6) s(-1) and (2.8 +/- 0.2) x 10(-11) cm(3) s(-1), respectively. In N-2, k(0) and k(infinity) are (1.1 +/- 0.2) x 10(-28) cm(6) s(-1) and (6.3 +/- 0.3) x 10(-11) cm(3) 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 O-2.