Measurements of temperature-dependent absorption cross sections of C2H2 inthe VUV-UV region

Using a synchrotron radiation as a continuum light source, we have carried out laboratory measurements of the temperature-dependent photoabsorption cr oss sections of C2H2 from 120 to 230 nm region at 295 K and from 120 to 215 nm region at 150 K with a spectral resolution of 0.007 nm. In the presentl y studied spectral region the cross section values vary by 6 orders of magn itude, and the absorption features vary from sharp rovibronic structure, sh aded bands, to diffuse bands. High-temperature cross sections of C2H2 in th e 120-140 nm region has also been measured for the purpose of identifying p ossible hot bands. The previous assignments: of Several hot bands in the 13 0-140 nm region were crucial in the determination of the electronic structu re of a valence E state. However, we find that the previously assigned hot bands at 135.09 and 136.24 nm are not hot bands at all because they are ins ensitive to temperature change from 150 to 370 K. The Galileo spacecraft ha s made incredibly successful observations of the Jovian system including th e prominent C2H2 auroral features, and the Jupiter flyby of the Cassini spa cecraft is yet to come. Equipped with higher-resolution spectrometers the C assini mission promises to provide higher scientific returns regarding the Jovian amoral observations. Solar and stellar occultation experiments at Sa turn by the Cassini spacecraft will provide more detailed observations of t he Saturnian upper atmosphere than ever before. The data presented in the p resent work are an extension of our effort to provide the required data to the scientific community and will have a significant impact on our understa nding of the atmospheres of Jupiter and Saturn, in particular, and other ou ter planets and satellites, in general.