The results of 4.2-K photodesorption experiments in two quasiclosed geometries are reported, (1) a simple tube and (2) a tube with a coaxial perforated linear. These experiments were designed to measure separately the desorption coefficients of tightly bound and physisorbed molecules. The results are important for the beam tube vacuum of the next generation of superconducting proton colliders that have been contemplated-the 20-TeV Superconducting Super Collider in the United States and the 7.3-TeV Large Hadron Collider at CERN.