The adsorption of CO and O 2 on Ni(111) at 8 K is studied by molecular beam techniques coupled with high resolution electron energy loss spectroscopy and work function measurements. The work functions are measured by a retarding potential technique using the HREEL spectrometer. The cryogenic crystal temperatures are attained by use of a liquid helium cryostat described in detail. The total and normal components of the translational energy of the incident molecules are lowered to 0.3 and 0.02 kcal mol −1, respectively. No evidence for a trapped, physisorbed CO molecule or a physisorbed molecular O 2 species is observed in the limit of zero coverage.