LOW-TEMPERATURE INTERACTION OF HYDROGEN WITH METHANE-PRECOVERED THIN PALLADIUM FILMS

The interaction of hydrogen with methane-precovered thin palladium fil ms at 78 K has been studied by means of a combination of thermal desor ption mass spectrometry (TDMS) and surface potential change (DELTASP) measurements. The results show that preadsorption of methane under hig h pressure (almost-equal-to 1 Torr) strongly hinders the adsorption an d incorporation of hydrogen atoms into the bulk of Pd films. Only expo sure to a pressure of H-2 greater-than-or-equal-to 10(-3) Torr leads t o PdH(x) formation. Decomposition of the bulk PdH(x) is limited by the preadsorbed CH4. The TD spectra point to a significant enrichment of subsurface and surface states of hydrogen due to interaction with prea dsorbed methane.