Continuous wave CEMOR for measurement of HO_2

摘要

Current combustion chemistry models are lacking detail in the low and intermediate temperature region where hydroxyl (OH), hydroperoxy (HO_2), and alkylperoxy (RO_2) radicals control the oxidation chemistry. Measurement of these radicals is difficult in combustion systems because of spectral overlap with stable products of combustion, such as CO_2 and H_2O. Therefore, there is a need for sensitive and selective diagnostics which can quantitatively measure these weakly absorbing small peroxy radicals in combustion systems. The authors have approached this need by applying a sensitive and selective laser diagnostic technique called Cavity Enhanced Magneto-Optic Rotation (CEMOR) for quantitative measurement of paramagnetic species, specifically HO_2 radicals. CEMOR combines the sensitivity of cavity ringdown spectroscopy (CRDS) and the selectivity of magneto-optic rotation (MOR) spectroscopy. This work presents a novel design of CEMOR with a continuous wave laser source for measurement of HO_2. The narrower bandwidth of continuous wave lasers offers increased spectroscopic resolution over the pulsed Nd:YAG/OPO laser used for previous CEMOR development. Continuous wave cavity ringdown spectroscopy (cw-CRDS) is integrated with MOR in order to make high-resolution scans of the HO_2 spectra. The present method can easily be adapted for alkyl peroxy (RO_2) radicals. Demonstration of the effect of magnetic field strength on the MOR signal is presented. Remaining challenges are discussed.