CO ADSORPTION-ISOTHERMS ON CU(100) AT ELEVATED PRESSURES AND TEMPERATURES USING INFRARED REFLECTION ABSORPTION-SPECTROSCOPY

Infrared reflection-absorption spectroscopy (IRAS) has been used to study the adsorption of carbon monoxide on a Cu(100) surface. Adsorption isotherms were determined at CO pressures from 10(-6) to 10 Torr, and at temperatures from 115 to 340 K, and the isosteric heats of adsorption (DELTA-E(ads)) evaluated as a function of CO coverage. For increasing CO coverages between 0-0.15 monolayers (ML), DELTA-E(ads) decreases sharply from 16.7 to 12.7 kcal/mol. From 0.15 to 0.35 ML, DELTA-E(ads) remains approximately 12.7 kcal/mol and exhibits little coverage dependence. These results are in excellent agreement with previously reported data for the CO/Cu(100) system acquired at much lower pressures (< 10(-4) Torr) and temperatures (< 275 K). At substrate temperatures above 240 K and at pressures > 10(-4), significant bathochromic shifts of the CO stretch frequency to lower wavenumbers are observed.