Laboratory spectroscopic studies of atmospherically important radicals using fourier transform spectroscopy |
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| Authors: | P T Wassell R P Wayne Ballard W B Johnston |
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| Institution: | (1) Physical Chemistry Laboratory, South Parks Road, OX1 3QZ Oxford, U.K.;(2) Rutherford Appleton Laboratory, Chilton, OX11 0QX Oxford, U.K. |
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| Abstract: | This paper describes laboratory experiments designed to obtain the infrared spectra of some atmospherically important radical species and related compounds. A Fourier transform spectrometer was used that was capable of yielding resolutions as great as 0.0024 cm-1, and optical paths of up to 512 m were employed. The objective of the experiments was to obtain the spectra for subsequent application to remote sounding measurements in the atmosphere.Radicals were generated by a variety of chemical reactions involving atoms or other highly reactive precursors. Spectra of the  3 band of NO3, at ca. 1500 cm-1, were obtained with up to 0.005 cm-1 resolution using the reaction between NO2 and O3 to produce the radical. The most satisfactory source of ClO was found to be the reaction between Cl and O3, and the (1-0) vibration-rotation band in the region 829–880 cm-1 was recorded at a resolution of 0.02 cm-1. We were unable to observe infrared absorption of HO2 with any of the radical sources that we tested. High-resolution survey spectra were obtained of compounds used as reactants, or formed as side-products in the radical-generating processes. These compounds included N2O5, HNO3, ClONO2, FNO2, Cl2O, HO2NO2, and probably FO2.The ability to monitor concentrations of the NO3 radical in the visible region of the spectrum as well as the concentrations of reactants and other products in the infrared region allowed us to undertake a study of the time-dependent interactions occurring when NO2 reacts with O3. The results indicate the importance of heterogeneous processes, especially when traces of water are present, and lend credence to suggestions that heterogeneous mechanisms in the NO3–N2O5–H2O system might be a viable source of HNO3 in the atmosphere. |
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| Keywords: | Fourier transform nitrate ozone spectroscopy radicals |
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