Temperature dependence of UV absorption cross sections and atmospheric implications of several alkyl iodides
Abstract
The ultraviolet absorption spectra of a number of alkyl iodides which have been found in the troposphere, CH_3I, C_2H_5I, CH_3CH_2CH_2I, CH_3CHICH_3, CH_2I_2, and CH2_ClI, have been measured over the wavelength range 200–380 nm and at temperatures between 298 and 210 K. The absorption spectra of the monoiodides C_H3I, C_2H_5I, CH_3CH_2CH_2I, and CH_3CHICH_3 are nearly identical in shape and magnitude and consist of single broad bands centered near 260 nm. The addition of a chlorine atom in CH_2ClI shifts its spectrum to longer wavelengths (σ_(max) at 270 nm). The spectrum of CH_2I_2 is further red‐shifted, reaching a maximum of 3.85×10^(−18) cm^2 molecule^(−1) at 288 nm and exhibiting strong absorption in the solar actinic region, λ>290 nm. Atmospheric photolysis rate constants, J values, have been calculated assuming quantum efficiencies of unity for different solar zenith angles as a function of altitude using the newly measured cross sections. Surface photolysis rate constants, calculated from the absorption cross sections measured at 298 K, range from 3×10^(−6) s^(−1) for CH)3I to 5×10^(−3) s^(−1) for CH)2I)2 at a solar zenith angle of 40°.
Additional Information
© 1997 by the American Geophysical Union. (Received November 14, 1996; revised February 12, 1997; accepted February 12, 1997.) Research at MPI was funded through the Max-Planck-Gesellschaft. The work at NOAA was funded in part by NASA's Upper Atmospheric Research Program.Attached Files
Published - Roehl_et_al-1997-Journal_of_Geophysical_Research_3A_Atmospheres.pdf
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Additional details
- Eprint ID
- 91291
- Resolver ID
- CaltechAUTHORS:20181128-113208441
- Max-Planck-Gesellschaft
- NASA
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2018-11-28Created from EPrint's datestamp field
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2021-11-16Created from EPrint's last_modified field