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

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 H₂ 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.