Rate Constant and Thermochemistry for K + O2 + N2 = KO2 + N2

• Published in: The journal of physical chemistry. A, Molecules, spectroscopy, kinetics, environment, & general theory Vol. 119; no. 14; pp. 3329 - 3336
• Main Authors: Sorvajärvi, Tapio, Viljanen, Jan, Toivonen, Juha, Marshall, Paul, Glarborg, Peter
• Format: Journal Article
• Language: English
• Published: United States American Chemical Society 09.04.2015
• ISSN: 1089-5639; 1520-5215
• DOI: 10.1021/acs.jpca.5b00755

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, k R1, whereas at higher temperatures equilibration was observed in the form of double exponential decays of [K], which yielded both k R1 and the equilibrium constant for KO2 formation. k R1 can be summarized as 1.07 × 10–30(T/1000 K)−0.733 cm6 molecule–2 s–1. Combination with literature values leads to a recommended k R1 of 5.5 × 10–26 T –1.55 exp­(−10/T) cm6 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 ΔS 298 yields a K–O2 bond dissociation enthalpy of 184.2 ± 4.0 kJ mol–1 at 298 K and Δf H 298(KO2) = −95.2 ± 4.1 kJ mol–1. The corresponding D 0 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.