Molecular desorption by synchrotron radiation and sticking coefficient temperatures for H$_{2}$, CH$_{4}$, CO and CO$_{2}$

A cryogenic vacuum system has been used to study both the surface pumping of gases and the molecular photodesorption yield from OFE copper in the temperature range from 5 K to 300 K. The sticking coefficient on a `bare surface´ was found to increase with decreasing temperature of the substrate and below 20 K, to be in the range of a few percent for all gas species studied. The molecular photodesorption yield for the `bare surface´ was found to decrease with decreasing temperature and below 20 K, after an accumulated photon dose of 3.1 1022 photons m-1, to be in the range of 10-4 molecules photon-1 for H2 and 10-5 molecules photon-1 for the other gas species. These measured values are used to predict the evolution of the gas densities in the LHC. Implications to the LHC are discussed.