KINETIC-STUDY OF THE REACTION OF IR(A(4)F(9 2)) WITH CH4, O-2, AND N2O/

The gas-phase reactivity of ground-state Ir(a(4)F(9/2)) with CH4, O-2, and N2O is reported. Iridium atoms were produced by the photodissocia tion of [Ir(CO)(2)(acac)] and detected by laser-induced fluorescence. The reaction rate of the a(4)F(9/2) state with CH4 is very slow and te mperature-dependent. The methane reaction is pressure-independent indi cating a bimolecular reaction. The bimolecular rate constant from 398 to 398 K is described in Arrhenius form by (7 +/- 5) x 10(-11) exp(-37 +/- 3 kJ/mol/RT) where the uncertainties represent +/-2 sigma. The re action rates of the a(4)F(9/2) state with O-2 and N2O are pressure-dep endent, indicating adduct formation. The limiting low-pressure third-o rder, k(0), and limiting high-pressure second-order, k(infinity), room -temperature rate constants with O-2 in nitrogen buffer are (4.8 +/- 1 .6) x 10(-30) cm(6) s(-1) and (3.6 +/- 0.4) x 10(-12) cm(3) s(-1), res pectively. For N2O, k(0) and k(infinity) are (2.2 +/- 0.5) x 10(-33) c m(6) s(-1) and (5.9 +/- 0.8) x 10(-15) cm(3) s(-1), respectively. A lo wer limit for the activation energy for the abstraction of an oxygen a tom from N2O to produce IrO is estimated at 45 kJ/mol.