ELIMINATION OF SERIOUS ARTIFACTS IN TEMPERATURE-PROGRAMMED DESORPTION SPECTROSCOPY

Regurgitation and wall displacement processes are often encountered in temperature programmed desorption measurements. Such effects can lead to misleading interpretations of the surface reaction and desorption products. A simple and useful pumping scheme is described which overcomes this problem by using a cryogenically cooled titanium sublimation pump (TSP) for differential pumping of the mass spectrometer. It is demonstrated that minor wall displacement effects (mainly CO, H2O, and H-2) are present in temperature programmed desorption spectroscopy and are insensitive to the mode of differential pumping. In comparison to ion pumping, however, serious methane (CH4) regurgitation and displacement effects can be completely eliminated when the TSP is employed.