High‐resolution, low‐temperature photoabsorption cross sections of C2H2, PH3, AsH3, and GeH4, with application to Saturn's atmosphere

Abstract

Using synchrotron radiation as a continuum background light source, the VUV absorption cross sections of (1) C2H2 and PH3 have been obtained under physical conditions approximating the stratosphere of Saturn and (2) AsH3 and GeH4 have been obtained under room temperature conditions. We have combined these new laboratory measurements with International Ultraviolet Explorer observations of the albedo of Saturn, for which improved data reduction techniques have been used, to produce new models for that atmosphere. When the effects of C2H2 absorption are accounted for, additional absorption by other molecules is required. The best fitting model also includes absorption by H2O, CH4, C2H6, PH3, and GeH4. The abundance of H2O is reduced by a factor of 2 as a direct consequence of the new low‐temperature cross section data of C2H2. The model abundance distributions of PH3 and GeH4 on Saturn decrease with increasing altitude, suggesting a possible consequence of UV photolysis.