Kinetic study of the recombination reaction of gas phase Pd(a1S0) with O2 from 294 to 523 K

The gas-phase removal rate constants for the reaction of ground-state palladium (a(1)S(0)) with oxygen in argon buffer are reported as a function of temperature and pressure. Palladium atoms were produced by the photodissociation of palladium(II) trifluoroacetate and detected by laser-induced fluorescence. The reaction is pressure dependent, indicating recombination to form PdO2. Falloff behavior is observed at pressures above about 20 Torr. Quantum calculations indicate that the reaction proceeds on a triplet surface to form bent PdO2((3)A"), which has a low frequency bending mode of only 129 cm(-1) and a bond energy D-0 = 95 kJ mol(-1). RRKM theory, fitted to the experimental data, shows that D-0 should lie below 155 kJ mol(-1) and predicts the following expression for the rate coefficient from 200 to 600 K: k(rec,0) = 1.09 x 10(-30) (T/300 K)(-2.76) cm(6) molecule(-2) s(-1), k(rec,infinity) = 2.52 x 10(-10) exp(-69.3/T) cm(3) molecule(-1) s(-1), and F-c = 0.61.