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) C 2 H 2 and PH 3 have been obtained under physical conditions approximating the stratosphere of Saturn and (2) AsH 3 and GeH 4 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 C 2 H 2 absorption are accounted for, additional absorption by other molecules is required. The best fitting model also includes absorption by H 2 O, CH 4 , C 2 H 6 , PH 3 , and GeH 4 . The abundance of H 2 O is reduced by a factor of 2 as a direct consequence of the new low‐temperature cross section data of C 2 H 2 . The model abundance distributions of PH 3 and GeH 4 on Saturn decrease with increasing altitude, suggesting a possible consequence of UV photolysis.