Kinetics of the reactions of HO with methanol (210–351 K) and with ethanol (216–368 K)

Abstract

Absolute rate coefficients for the reaction of hydroxyl radicals (HO) with methanol, HO + CH₃OH → products (R1), and with ethanol, HO + C₂H₅OH → products (R2) were measured over a range of temperatures using pulsed laser photolytic generation of HO coupled to its time resolved detection by pulsed laser induced fluorescence. The accuracy of the rate constants obtained was enhanced by on-line optical absorption measurements of the alcohol concentration. The temperature dependence of the rate coefficients is given by: k₁(210–351 K) = 6.67 × 10⁻¹⁸T² exp(140/T) cm³ molecule⁻¹ s⁻¹ with a rate coefficient at room temperature of (9.3 ± 0.7) × 10⁻¹³ cm³ molecule⁻¹ s⁻¹. For k₂ we obtained: k₂(216–368 K) = 4.0 × 10⁻¹² exp(−42/T) and a room temperature rate coefficient of (3.35 ± 0.17) × 10⁻¹² cm³ molecule⁻¹ s⁻¹. The total error (at 95% confidence) associated with the rate coefficients derived from the expressions describing the temperature dependence is estimated as 7% at all temperatures. The present results, which extend the database on these reactions to cover temperatures relevant for the upper troposphere, are compared to previously published measurements, and values of k₁ and k₂ are recommended for atmospheric modelling.