Pressure and temperature dependence of the gas-phase recombination of hydroxyl radicals

Abstract

Rate constants for the reaction OH + OH + M -H202 + M (M = N2, H20) have been determined by using flash photolysis of H20 vapor in combination with quantitative OH resonance spectrometry. For M = N2 experiments were performed at 253, 298, and 353 K and at pressures between 26 and 1100 mbar. Under these conditions the reaction is found to be primarily in the low-pressure limit with £1iN2°( T = 298 K) = (6.9*lf) x 10~31 cm6/s and a temperature dependence of T~o i. Both the absolute value of k^N°a nd its temperature variation are in very satisfactory agreement with theoretical predictions and extrapolations from high-temperature dissociation data. A pressure falloff of £1N2 is also observed. On the basis of a theoretical analysis of the falloff behavior, a high-pressure limiting rate coefficient of kf = 1.5 X 10"" cm3/s, independent of temperature, is predicted. From experiments in N2/H20 mixtures with xHl0 = 0.11 at pressures up to 140 mbar a low-pressure limiting rate coefficient for H20 as a third body of ki,H2o°( T = 298 K) = (4.022o) x 10'30 cm6/s is obtained.

An improved H2/O2 mechanism based on recent shock tube/laser absorption measurements

“…Both theoretical calculations resulted in much larger k 3,1 values than the one recommended by Kappel et al [58]. The larger k 3,1 values from these two theoretical studies [13,14] are supported by high-pressure studies at room temperature [59,61].…”

“…In the current mechanism, the O 2 collider efficiency is set equal to that of N 2 . Suggested values for the collider efficiencies of H 2 O relative to N 2 have been estimated to be 6 or 9 relative to Ar based on early roomtemperature studies by Zellner et al [59] and Forster et al [60].…”

An optimized kinetic model of H2/CO combustion

“…The trial model was based on a careful review of recent kinetics literature, considering both direct data and compilations. A large number of GRI 3.0 rate parameters [8] were 1540 For OH + OH(+M) = H 2 O 2 (+M), the k 0 expression, given in the reverse direction by Baulch et al [12], was refitted based on the new heat of formation of the OH radical along with the low temperature data of Zellner et al [11]. The k rec,1 expression and the b value of H 2 O (6) were taken from [11] while the Troe fall-off parameters [22] were the same as those in GRI 3.0.…”

“…A large number of GRI 3.0 rate parameters [8] were 1540 For OH + OH(+M) = H 2 O 2 (+M), the k 0 expression, given in the reverse direction by Baulch et al [12], was refitted based on the new heat of formation of the OH radical along with the low temperature data of Zellner et al [11]. The k rec,1 expression and the b value of H 2 O (6) were taken from [11] while the Troe fall-off parameters [22] were the same as those in GRI 3.0. The rate expressions for H 2 O 2 + OH = HO 2 + H 2 O were taken directly from [15], though the high-temperature expression was refitted using a modified Arrhenius expression to avoid the rate constant values exceeding the collision limit when extrapolated to high temperatures.…”

Measurement of the Rate of Hydrogen Peroxide Thermal Decomposition in a Shock Tube Using Quantum Cascade Laser Absorption Near 7.7 μm

“…The reverse recombination reaction (OH + OH) has also been investigated experimentally by flash photolysis of OH precursors to produce OH radials . Trainer and von Rosenberg performed experiments at room temperature and subatmospheric pressure.…”