An OH Monitoring Method Using Infrared-Ultraviolet Double Resonance Laser-Induced Fluorescence

摘要

We have applied an infrared-ultraviolet double resonance laser-induced fluorescence (IR-UV LIF) technique to the measurment of OH concentrations in the troposphere. This OH exists in extremely low concentrations, ca. 10~6 molecules cm~(-3), and plays a central role in the atmospheric chemistry. The detection limit of this new technique using our laser and detection system was experimentally determined to be 1.3 x 10~9 molecules cm~(-3) at 9.2 mTorr in Ar buffer gas. We have found that the method is free from chemical interferences but less sensitive than the single photon LIF method. A simple model is formulated and differential equations are numerically solved after the selection and determination of necesary physical constants. The method leads to the simulated (single photon LIF)/(IR-UV LIF) sensitivity ratio of 1.4 x 10~3, comparable with the experimental value of 2.2 x 10~3. On the basis of the proposed kinetic model, we discuss the optimum experimental parameters (sample pressure, IR and UV laser powers, and delay time) in this IR-UV LIF method by taking account of rotational energy transfer, fluorescence quenching, and saturation of absorption.