ELECTRON-STIMULATED DESORPTION OF NO FROM STEP SITES ON PT(112) - THEROLE OF CHEMISORPTION SITE GEOMETRY ON THE CROSS-SECTION

The electronic excitation of adsorbed NO on Pt(112) has been observed to cause mainly desorption. Species-specific total desorption cross se ctions of terminally bound and bridged-bound NO present exclusively on the step sites of Pt(112) have been measured using Fourier transform infrared reflection absorption spectroscopy (FT-IRAS) as a sensitive d etector of the surface coverage of various chemisorbed NO species.' Ot her electron stimulated processes which might influence the measuremen t of these cross sections, such as electron stimulated fragmentation, site-exchange, and occupied site density effects have been found to be unimportant. It was found for 275 eV electrons that terminally bound NO desorbs with a larger cross section (2.3 X 10(-18) cm(2)) than brid ged-bound NO, which has a desorption cross section of 8.7 X 10(-19) cm (2). This is the expected relationship between the total desorption cr oss sections for these two species, with the smaller cross section bei ng observed for the bridged NO.