High-temperature measurements of VUV-absorption cross sections of CO sub(2)and their application to exoplanets

Ultraviolet (UV) absorption cross sections are an essential ingredient of photochemical atmosphere models. Exoplanet searches have unveiled a large population of short-period objects with hot atmospheres, very different from what we find in our solar system. Our goal is to provide high-temperature absorption cross sections and their temperature dependency for important atmospheric compounds. This study is dedicated to CO[sub 2], which is observed and photodissociated in exoplanet atmospheres. We performed these measurements with synchrotron radiation as a tunable VUV light source for the 115-200 nm range at 300, 410, 480, and 550 K. In the 195-230 nm range, we used a deuterium lamp and a 1.5 m Jobin-Yvon spectrometer and we worked at seven temperatures between 465 and 800 K. The model predicts that accounting for this temperature dependency of CO[sub 2] cross section can affect the computed abundances of NH[sub 3], CO[sub 2], and CO by one order of magnitude in the atmospheres of hot Jupiter and hot Neptune. This effect will be more important in hot CO[sub 2]-dominated atmospheres.