ADSORPTION ISOBARS FOR CO ON PD TA(110) AT ELEVATED PRESSURES AND TEMPERATURES USING INFRARED REFLECTION-ABSORPTION SPECTROSCOPY/

Infrared reflection-absorption spectroscopy (IRAS) has been used to st udy the adsorption of carbon monoxide on a Pd/Ta(110) surface. IRAS sp ectra were collected at pressures from 1 x 10(-9) to 1.0 Torr and at t emperatures from 90 to 500 K, Adsorption isobars were constructed from the IRAS spectra that allowed the determination of isosteric heats of adsorption as a function of CO coverage. The heats of adsorption (DEL TAH) for CO on Pd/Ta(110) were determined to be approximately 15 kcal/ mol lower than for CO adsorbed on a Pd(111) surface while the differen tial surface entropies (S(s)) were comparable. The high coverage adsor ption isosteres have a pronounced break that indicates that at high CO coverages and low substrate temperatures, the CO surface structures a re not fully equilibrated.