The technique of infrared emission spectroscopy has been developed in order to observe vibrational modes of molecules adsorbed on clean, single crystal metal surfaces. A novel apparatus has been constructed which measures the emission from a single crystal sample in thermal equilibrium at room temperature. The apparatus consists of a liquid helium cooled infrared grating spectrometer coupled to an ultrahigh vacuum system equipped with surface preparation and characterization facilities. The system is capable of measuring over the frequency range from 330 to 3000 cm-1with a resolution of 1 to 15 cm-1. Using this technique, we have measured the linewidths of both the carbon-metal and carbon-oxygen stretching vibrations of monolayer coverage of CO on Ni(100). © 1984, American Vacuum Society. All rights reserved.