Heat of Adsorption of Propyne on Cu(111) from Isotherms Measured by Reflection Absorption Infrared Spectroscopy

Reflection absorption infrared spectroscopy (RAIRS) has been used to show that under pressures of 5-100 nTorr, propyne adsorbs reversibly at room temperature on the Cu(111) surface. The pressure dependence of the propyne coverage, based on RAIRS peak areas, was found to follow a Langmuir isotherm. From fits of the isotherms, the equilibrium constants for the adsorption were determined at temperatures from 300.0 to 307.5 K. From van't Hoff plots of the temperature dependence of the equilibrium constant, a heat of adsorption of -120 +/- 27 kJ mol(-1) and an entropy change of adsorption of -171 +/- 88 J mol(-1) K-1 were determined. These values are consistent with the corresponding literature values of similar systems.