Propene adsorption on Ag(111): a TPD and RAIRS study

We have investigated the interactions of propene with Ag(I 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 (alpha(1) state), 145 K (alpha(2) state) and 123 K (alpha(3) state) sequentially populated as the coverage increases. These are ascribed to two slightly different adsorption states involving Ag (alpha(1) and alpha(2)) and multilayer (alpha(3)), respectively. Repulsive interactions drive a change from alpha(1)- to alpha(2)-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(I 1 1) surface for the alpha(1) and alpha(2) adsorption states but is tilted away for the multilayer alpha(3) adsorption state. (C) 2002 Elsevier Science B.V. All rights reserved.