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The HO 2 + CH 3 C(O)O 2 reaction consists of three product channels: CH 3 C(O)OOH + O 2 (R1a), CH 3 C(O)OH + O 3 (R1b), and OH + CH 3 C(O)O + O 2 (R1c). The overall rate constant ( k 1 ) and product yields (α 1a , α 1b , and α 1c ) were determined over the atmospherically relevant temperature range of 230-294 K at 100 Torr in N 2 . Time-resolved kinetics measurements were performed in a pulsed laser photolysis experiment in a slow flow cell by employing simultaneous infrared (IR) and ultraviolet (UV) absorption spectroscopy. HO 2 and CH 3 C(O)O 2 were formed by Cl-atom reactions with CH 3 OH and CH 3 CHO, respectively. Heterodyne near- and mid-infrared (NIR and MIR) wavelength modulation spectroscopy (WMS) was employed to selectively detect HO 2 and OH radicals. Ultraviolet absorption at 225 and 250 nm was used to detect various peroxy radicals as well as ozone (O 3 ). These experimental techniques enabled direct measurements of α 1c and α 1b via time-resolved spectroscopic detection in the MIR and the UV, respectively. At each temperature, experiments were performed at various ratios of initial HO 2 and CH 3 C(O)O 2 concentrations to quantify the secondary chemistry. The Arrhenius expression was found to be k 1 ( T) = 1.38 -0.63  +1.17 × 10 -12  exp[(730 ± 170)/ T] cm 3 molecule -1 s -1 . α 1a was temperature-independent while α 1b and α 1c decreased and increased, respectively, with increasing temperatures. These trends are consistent with the current recommendation by the IUPAC data evaluation. Hydrogen-bonded adducts of HO 2 with the precursors, HO 2 ·CH 3 OH and HO 2 ·CH 3 CHO, played a role at lower temperatures; as part of this work, rate enhancements of the HO 2 self-reaction due to reactions of the adducts with HO 2 were also measured.

the journal of physical chemistry a

Temperature Dependence Study of the Kinetics and Product Yields of the HO2 + CH3C(O)O2 Reaction by Direct Detection of OH and HO2 Radicals Using 2f-IR Wavelength Modulation Spectroscopy