THE PRECURSOR STATE TO DISSOCIATION OF CO ADSORBED ON THE W(110) SURFACE - SOME ASPECTS OF CO ADSORPTION ON W(110) AT LOW COVERAGE

The work function change versus exposure for CO on W(110) at various temperatures has been measured via the Kelvin method. We find essentially linear rise with coverage at T(s) less-than-or-equal-to 200 K in agreement with a previous determination by Wang and Gomer [C. Wang and R. Gomer, Surf. Sci. 74 (1978) 389] but in disagreement with a recent measurement by Houston [J.E. Houston, Surf. Sci. 225 (1991) 303] based on changes in secondary electron emission with CO coverage for 2000 eV incident electrons. We have also measured the ratio of 4sigma to (5sigma + 1pi) peaks in UPS at 21.2 and 40.8 eV photon energies at relative CO coverages of 1 of 0.3-0.25. For 21.2 eV photons the 4sigma peak virtually disappears at theta = 0.3, but at 40.8 eV 4sigma/(5sigma + 1pi) is greater at theta = 0.25 than at theta = 1. The present results do not contradict the tilted CO configuration at low coverage suggested by Houston's C-O stretch results, but do not lend it direct support.