Experimental Study of the Rate of OH + HO₂ → H₂O + O₂ at High Temperatures Using the Reverse Reaction

Abstract

The rate constant of the reaction OH + HO(2) --> H(2)O + O(2) (1) can be inferred at high temperatures from measurements of the rate of its reverse reaction H(2)O + O(2) --> OH + HO(2) (-1). In this work, we used laser absorption of both H(2)O and OH to study the reverse reaction in shock-heated H(2)O/O(2)/Ar mixtures over the temperature range 1600-2200 K. Initial H(2)O concentrations were determined using tunable diode laser absorption near 2.5 microm, and OH concentration time-histories were measured using UV ring dye laser absorption near 306.7 nm. Detailed kinetic analysis of the OH time-history profiles yielded a value for the rate constant k(1) of (3.3 +/- 0.9) x 10(13) [cm(3) mol(-1) s(-1)] between 1600 and 2200 K. The results of this study agree well with those reported by Srinivasan et al. (Srinivasan, N.K.; Su, M.-C.; Sutherland, J.W.; Michael, J.V.; Ruscic, B. J. Phys. Chem. A 2006, 110, 6602-6607) in the temperature regime between 1200 and 1700 K. The combination of the two studies suggests only a weak temperature dependence of k(1) above 1200 K. Data from the current study and that of Keyser (Keyser, L.F. J. Phys. Chem. 1988, 92, 1193-1200) at lower temperatures can be described by the k(1) expression proposed by Baulch et al. (Baulch, D.L.; Cobos, C.J.; Cox, R.A.; Esser, C.; Frank, P.; Just, Th.; Kerr, J.A.; Pilling, M.J.; Troe, J.; Walker, R.W.; Warnatz, J. J. Phys. Chem. Ref. Data 1992, 21, 411), k(1) = 2.89 x 10(13) exp(252/T) [cm(3) mol(-1) s(-1)]. However, it should be noted that some previous studies suggest a k(1) minimum around 1250 K (Hippler, H.; Neunaber, H.; Troe, J. J. Chem. Phys. 1995, 103, 3510-3516) or 1000 K (Kappel, C.; Luther, K.; Troe, J. Phys. Chem. Chem. Phys. 2002, 4, 4392-4398).

Comprehensive H2/O2 kinetic model for high‐pressure combustion

“…Substitution of different proposed expressions [75][76][77] that give higher weighting to the other set of intermediate data from Troe and coworkers [69] degrades flame predictions for lean, high-pressure flames. None of the proposed expressions [75][76][77] that incorporate the intermediate data [22,69], as well as the expression from [78], reproduce the more direct, recent measurements of Hong et al [71] on the reverse reaction at high temperatures. Given the lack of consistency among experimental data regarding this reaction at intermediate temperatures, lack of theoretical support for the pronounced rate constant minimum, and the incompatibility of the expressions from [75][76][77] with the set of other rate parameters used in the present model, the present model retains the rate constant expression proposed by Keyser [63], which is used in our previous model [12].…”

“…The data of Srinivasan et al [70] over the temperature range from 1200 to 1700 K do not exhibit a strong temperature dependence. More recent determinations of (R13) from 1600 to 2200 K by Hong et al [71] based on rate constant measurements of the reverse reaction reveal a slight negative temperature dependence. Their more direct determinations of k 13 [71] are a factor of two lower than previous high-temperature determinations from flame studies [72,73].…”

“…More recent determinations of (R13) from 1600 to 2200 K by Hong et al [71] based on rate constant measurements of the reverse reaction reveal a slight negative temperature dependence. Their more direct determinations of k 13 [71] are a factor of two lower than previous high-temperature determinations from flame studies [72,73]. In addition, their measurements are well described by the rate expression proposed by Keyser [63] based solely on atmospheric temperature measurements.…”

“…The validation set here includes the full validation set from our previous models [12,47] as well as more recent measurements that have become available since the publication of the model of Li et al [12]; many of these newly available measurements focus on high-pressure, low-temperature conditions. For example, new measurements have become available for speciation during H 2 oxidation [42], H 2 O reaction with O 2 [71], and H 2 O 2 decomposition [87,92]; ignition delay times in shock tubes [10] and rapid compression machines (RCM) [11]; and flame speeds and mass burning rates [5][6][7][8][9].…”

IR laser absorption diagnostic for C2H4 in shock tube kinetics studies

“…In future work, the H 2 O concentration during hydrocarbon oxidation could be measured directly and accurately using tunable diode laser absorption near 2.5 μm, a method which has been developed and widely applied in shock tube studies of H 2 /O 2 combustion system in our laboratory [13,23,24]. Alternatively, a second CO 2 line (i.e., the P(28) transition at 10.675 μm), which is away from the peak ethylene absorption, could be selected to account for the H 2 O interfering absorbance.…”