A. C. NOELL, L. S. ALCONCEL, D. J. ROBICHAUD AND M. OKUMURA, Department of Chemistry, California Institute of Technology, Pasadena, CA 91125; S. P. SANDER, Jet Propulsion Laboratory, Pasadena, CA 91109.
Reactions between RO2 and HO2 are important in the gas phase oxidation of volatile organics in the atmosphere. The rate constants for the reactions of HO2 + C2H5O2, and C2H5O2 + C2H5O2 were measured using a novel approach to radical radical reactions that employs two independent spectroscopic probes. HO2 was monitored at 6638.2 cm-1 using near-IR diode laser WM spectroscopy, and C2H5O2 was monitored at 250 nm using UV absorption. Experiments were run under conditions relevant to the upper troposphere (221-298 K and 50-400 Torr). Measurements of the rate constants for both reactions as well as a measurement of the branching fraction leading to the alkoxy channel of the C2H5O2 self reaction will be discussed. Preliminary results are: kHC = (6.4\pm1.4)×10-13 cm3 molec-1 s-1 Exp((601\pm120)/ T ), kCC = (1.10\pm0.20)× 10-13 cm3 molec-1 s-1 independent of temperature, and a branching fraction of 0.32\pm0.13.