The ultraviolet absorption cross sections of CH3I temperature dependent gas and liquid phase measurements Original Research Article

The absorption cross section for methyl iodide (CH3I) have been measured in the gas phase from 160 to 335 nm and in the liquid phase from 330 to 400 nm over the temperature range 223–333 K. The liquid phase results were converted into effective gas phase cross sections using a wavelength shift procedure described and verified in earlier works. In the extremely strong discrete absorption system between 160 and about 210 nm the absorption cross sections decrease with decreasing temperature. In the continuous absorption region from about 210 to 270 nm the cross sections increase with decreasing temperature with the change being most pronounced near the peak at 258.5 nm. At wavelengths longer than about 270 nm the across sections once again decrease with decreasing temperature, with more pronounced changes occurring in the long wavelength tail of the absorption band. The use of these temperature dependent absorption cross sections should lead to improved accuracy of and confidence in atmospheric lifetime calculations for CH3I.