THE ULTRAVIOLET-ABSORPTION CROSS-SECTIONS OF CH3I TEMPERATURE-DEPENDENT GAS AND LIQUID-PHASE MEASUREMENTS

The absorption cross sections for methyl iodide (CH3I) have been measu red in the gas phase from 160 to 335 nm and in the liquid phase from 3 30 to 400 nm over the temperature range 223-333 K. The liquid phase re sults were converted into effective gas phase cross sections using a w avelength 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 temperat ure. In the continuous absorption region from about 210 to 270 nm the cross sections increase with decreasing temperature with the change be ing most pronounced near the peak at 258.5 nm. At wavelengths longer t han about 270 nm the cross sections once again decrease with decreasin g temperature, with more pronounced changes occurring in the long wave length tail of the absorption band. The use of these temperature depen dent absorption cross sections should lead to improved accuracy of and confidence in atmospheric lifetime calculations for CH3I.