Absolute Rate Constant Measurements of OH Reactions Under Atmospheric Conditions by Laser Photolysis/Dye Laser Fluorescence

Summary

Absolute rate constants of OH reactions have been measured under tropospheric conditions by applying the sensitive pulsed dye laser induced fluorescence technique for monitoring OH radicals as a function of reaction time. The results of test measurements with simple alkanes and alkenes at a total pressure of 1 atm of air were found to be in good agreement with literature data. Detailed measurements were performed on the reaction of OH with acetylene at 295 K. Similar pressure dependences of the reaction rate were measured for inert buffer gases (He, Ar, N₂) between 0.8 and 1053 mbar with rate constants in the range (0.9² − 8.0) · 10⁻¹³ cm³ s⁻¹. In the presence of O₂, the effective disappearance rate of OH was diminished at all total pressures by about a factor of four due to reproduction of OH by fast secondary processes. Besides the decay of OH, the formation and decay of vinoxy radicals as intermediates and the formation of glyoxal as a major product of the reaction in the presence of O₂ could be followed with the LIF technique.

For the reaction of SO₂ with OH at 1 atm total pressure a rate constant of (8.6 ± 2.0²) · 10⁻¹³ cm³ s⁻¹ was measured in Ar as well as in synthetic air as diluent gases excluding a major effect of O₂ on the reaction rate.