The self-reactions and cross reactions of the peroxy radicals C 2H5O2 and HO2 were monitored using simultaneous independent; spectroscopic probes to observe each radical species. Wavelength modulation (WM) near-infrared (NIR) spectroscopy was used to detect HO 2, and UV absorption monitored C2H2O 2. The temperature dependences of these reactions were investigated over a range of interest; to tropospheric chemistry, 221-296 K. The Arrhenius expression determined for the cross reaction, k2(T) = (6.01 +1.95 -1.47) x 10-13 exp((638 ± 73)/T) cm3 molecules-1 s-1 is in agreement with other work from the literature. The measurements of the HO2 self-reaction agreed with previous work from, this lab and were not further refined. The C2H5O2 self-reaction is complicated by secondary production of HO2. This experiment performed the first direct measurement of the self-reaction rate constant, as well as the branching fraction to the radical channel, in part; by measurement of the secondary HO2. The Arrhenius expression for the self-reaction rate constant is k3(T) = (1.29 +0.34 -0.27) x 10-13 exp((-23 ± 61)/T) cm3 molecules-1 s- and the branching fraction value is α = 0.28 ± 0.06, independent of temperature. These values are in disagreement with previous measurements based on end product studies of the blanching fraction. The results suggest that better characterization of the products from RO2 self-reactions are required.
ASJC Scopus subject areas
- Physical and Theoretical Chemistry