Propene adsorption on Ag(1 1 1): a TPD and RAIRS study

We have investigated the interactions of propene with Ag(1 1 1) by means of temperature programmed desorption (TPD) and reflection adsorption infrared spectroscopy (RAIRS). At 100 K, propene reversibly adsorbs, with desorption peaks at 161 K (α1 state), 145 K (α2 state) and 123 K (α3 state) sequentially populated as the coverage increases. These are ascribed to two slightly different adsorption states involving Ag (α1 and α2) and multilayer (α3), respectively. Repulsive interactions drive a change from α1- to α2-propene during adsorption and desorption. The three adsorption states are distinguished by RAIRS on the basis CH2 wagging vibration frequencies at 924, 918 and 908 cm−1, respectively. Relative intensities demonstrate that the plane containing the three carbon atoms lies nearly parallel to the Ag(1 1 1) surface for the α1 and α2 adsorption states but is tilted away for the multilayer α3 adsorption state.