Measurements of infrared absorption cross-sections for chloroiodomethane and 2-iodopropane from 305 to 340 K

Iodocarbons, such as chloroiodomethane (CH 2 ICl) and 2-iodopropane ( ), contribute to the cycling of iodine between the ocean and the atmosphere. Atmospheric iodine can lead to the formation of atmospheric aerosol and contribute to ozone loss. Chloroiodomethane and 2-iodopropane, in particular, are produced from biogenic sources, such as marine algae, and, together with other methylated halogens, have been proposed as capstone biosignatures to help confirm the presence of the primary biosignatures oxygen and methane. There exist limited infrared spectral data for both these compounds; we provide absorption cross-sections between 305 and 340 K at 0.01 cm − 1 resolution in the range 535–1600 and 850–1600 cm − 1 for chloroiodomethane and 2-iodopropane, respectively. These are the first infrared cross-section measurements of chloroiodomethane, to our knowledge. Density functional theory calculations are performed to determine the optimal density functional-basis set pair for chloroiodomethane and 2-iodopropane calculations, and to supplement experimental data. Integrated cross-sections and radiative efficiency values are calculated using both experimental and density functional theory cross-sections to verify the accuracy of density functionals and to compare results with literature data. Neither of these metrics shows any trend in temperature, and both agree with values from literature and density functional theory. Our best estimate for the radiative efficiency is 0.036 ± 0.008 and 0.031 ± 0.007 W m −2 ppbv −1 for chloroiodomethane and 2-iodopropane, respectively. • New and cross-sections from 305 to 340 K at 0.01 cm − 1 resolution. • First measurements of infrared absorption cross-sections. • Performed DFT calculations to find ideal functional-basis set for & . • Derived REs of 0.036 ± 0.008 for and 0.031 ± 0.007 W m −2 ppbv −1 for . • Showed temperature-independence of integrated cross-sections and climate metrics.