The surfaces of icy Solar System bodies are predominantly water ice, with small amounts of methane, carbon monoxide, carbon dioxide, nitrogen, and ammonia. The outer surfaces are constantly subject to photon irradiation and particle bombardment, the solar wind, cosmic rays, and chemical reactions on surfaces, in addition to thermal cycling. In this project, the collaborating team will continue, with renewed NSF support, their laboratory experiments on the physics of extreme ultraviolet (EUV)-vacuum ultraviolet (VUV) photolysis of cosmic ice analogs. They plan simultaneous investigations of photon-induced chemical reactions and photodesorption in ice analogs containing water and other relevant species. A tunable intense synchrotron radiation light source available at the National Synchrotron Radiation Research Center (NSRRC), Taiwan, will provide the required EUV-VUV photons. The team will identify the type of molecules that form in the ice samples, and those that come off the ice surfaces, quantify their production yields, understand their production mechanisms, the destruction yields (lifetimes or stabilities) of the parent ice molecule(s), and ascertain their significance in astronomical environments. Much of the sophisticated equipment and advanced experimental techniques required for the proposed work have been developed by the team with prior NSF funding. The results will be particularly relevant to understanding of the water-rich icy satellites of the giant planets, comets, the interstellar medium, molecular clouds, and protostellar regions. The research results will also be incorporated into teaching materials for advanced undergraduate and graduate courses. The project will train a postdoctoral associate and a graduate student, with an emphasis on working with a synchrotron radiation facility.