title: Rate constant and thermochemistry for K + O2 + N2 = KO2 + N2.
abstract: The addition reaction of potassium atoms with oxygen has been studied using the collinear photofragmentation and atomic absorption spectroscopy (CPFAAS) method. KCl vapor was photolyzed with 266 nm pulses and the absorbance by K atoms at 766.5 nm was measured at various delay times with a narrow line width diode laser. Experiments were carried out with O2/N2 mixtures at a total pressure of 1 bar, over 748-1323 K. At the lower temperatures single exponential decays of [K] yielded the third-order rate constant for addition, kR1, whereas at higher temperatures equilibration was observed in the form of double exponential decays of [K], which yielded both kR1 and the equilibrium constant for KO2 formation. kR1 can be summarized as 1.07 × 10(-30)(T/1000 K)(-0.733) cm(6) molecule(-2) s(-1). Combination with literature values leads to a recommended kR1 of 5.5 × 10(-26)T(-1.55) exp(-10/T) cm(6) molecule(-2) s(-1) over 250-1320 K, with an error limit of a factor of 1.5. A van't Hoff analysis constrained to fit the computed ΔS298 yields a K-O2 bond dissociation enthalpy of 184.2 ± 4.0 kJ mol(-1) at 298 K and ΔfH298(KO2) = -95.2 ± 4.1 kJ mol(-1). The corresponding D0 is 181.5 ± 4.0 kJ mol(-1). This value compares well with a CCSD(T) extrapolation to the complete basis set limit, with all electrons correlated, of 177.9 kJ mol(-1).
authors.affiliation: †Optics Laboratory, Department of Physics, Tampere University of Technology, P.O. Box 692, FI-33101 Tampere, Finland.
authors.forename: Tapio
authors.initials: T
authors.lastname: Sorvajärvi
authors.affiliation: †Optics Laboratory, Department of Physics, Tampere University of Technology, P.O. Box 692, FI-33101 Tampere, Finland.
authors.forename: Jan
authors.initials: J
authors.lastname: Viljanen
authors.affiliation: †Optics Laboratory, Department of Physics, Tampere University of Technology, P.O. Box 692, FI-33101 Tampere, Finland.
authors.forename: Juha
authors.initials: J
authors.lastname: Toivonen
authors.affiliation: ‡Department of Chemistry and Center for Advanced Scientific Computing and Modeling (CASCaM), University of North Texas, 1155 Union Circle #305070, Denton, Texas 76203-5017, United States.
authors.forename: Paul
authors.initials: P
authors.lastname: Marshall
authors.affiliation: §Department of Chemical and Biochemical Engineering, Technical University of Denmark, DK-2800 Kgs. Lyngby, Denmark.
authors.forename: Peter
authors.initials: P
authors.lastname: Glarborg