Kinetic study of the reactions of gas-phase V(a4F3/2), Cr(a7S3), Co(a4F9/2), Ni(a3F4, a3D3) and Zn(4s2 1S0) atoms with nitrous oxide

The reactivity of gas-phase V(a(4)F(3/2)), Cr(a(7)S(3)), Co(a(4)F(9/2)), Ni(a(3)F(4). a(3)D(3)), and Zn(4s(2) S-1(0)) with N2O as a function of temperature and pressure is reported. The transition metal atoms were produced by the photodissociation of an appropriate precursor molecule and detected by laser-induced fluorescence. The vanadium, chromium, and cobalt rate constants are independent of total pressure indicating bimolecular abstraction reactions. The bimolecular rate constants (in molecule(-1) cm(3) s-(1)) are described in Arrhenius form by k[V(a(4)F(3/2))] = (4.7 +/- 0.7) x 10(-11) exp(-10.8 +/- 0.5 kJ mol(-1)/RT), Cr(a(7)S(3)), (5.0 +/- 1.0) x 10(-11) exp-(-21.1 +/- 0.7 kJ mol(-1)/RT), and Co(a(4)F(9/2)), (1.9 +/- 0.3) x 10(-10) exp(-48.8 +/- 0.8 kJ mol(-1)/RT) where the uncertainties represent +/-2 sigma. The reactions of nickel with N2O are pressure dependent indicating adduct formation; however, the reaction also has a bimolecular component. The room-temperature-limiting low-pressure third-order and limiting high-pressure second-order rate constants are (8.2 +/- 2.4) x 10(-32) molecule(-2) cm(6) s(-1) and (1.3 +/- 1.2) x 10(-12) molecule(-1) cm(3) s(-1) in N-2 buffer, respectively. The second-order rate constant for the abstraction channel for the reaction of nickel with N2O at 298 K is (9.3 +/- 1.3) x 10(-14) molecule(-1) cm(3) s(-1). The reaction of zinc with N2O is very slow; at 623 K an upper limit of 1 x 10(-16) molecule(-1) cm(3) s(-1) is set for this reaction. An assessment of the semiempirical configuration interaction model used by Fontijn and co-workers to estimate barrier heights in these reactions is made.