The gas phase depletion kinetics of Nb(a6D J ,a4F J ) in the presence of O2, SO2, CO2, N2O, and NO are reported. Niobium atoms were produced by the 248 nm photodissociation of Nb(C5H5)(CO)4 and detected by laser-induced fluorescence. The ground term of Nb(4d45s a6D J ) reacts at or above the collision rate with all of the aforementioned oxidants. The first excited term, Nb(4d35s a4F J ), is not as reactive with these oxidants. Results are interpreted in terms of long-range attractions and valence interactions. Additionally, we report reaction rate constants for ground state Nb interacting with N2, CH4, and SF6. Nb(a6D J ) is unreactive toward CH4. Nb(a6D J ) + N2 is pressure dependent at 297 K with k 0 = (2.6 ± 0.3) × 10-32 cm6 s-1 and k ∞ = (4.1 ± 0.5) × 10-13 cm s-1. Nb(a6D J ) + SF6 is temperature dependent with the rate constants given by k(T) = (1.2 ± 0.3) × 10-10 exp[−(4.8 ± 0.2) kcal mol-1/RT] cm3 s-1. Depletion of the aF J term by N2, SF6, and CH4 is J-dependent.

No abstract

The reactivity of gas-phase V(a4F3/2), Cr(a7S3), Co(a4F9/2), Ni(a3F4, a3D3), and Zn(4s2 1S0) 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 cm3 s-1) are described in Arrhenius form by k[V(a4F3/2)] = (4.7 ± 0.7) × 10-11 exp(−10.8 ± 0.5 kJ·mol-1/RT), Cr(a7S3), (5.0 ± 1.0) × 10-11 exp(−21.1 ± 0.7 kJ·mol-1/RT), and Co(a4F9/2), (1.9 ± 0.3) × 10-10 exp(−48.8 ± 0.8 kJ·mol-1/RT) where the uncertainties represent ±2σ. 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) × 10-32 molecule-2 cm6 s-1 and (1.3 ± 1.2) × 10-12 molecule-1 cm3 s-1 in N2 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) × 10-14 molecule-1 cm3 s-1. The reaction of zinc with N2O is very slow; at 623 K an upper limit of 1 × 10-16 molecule-1 cm3 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.

No abstract