Control and FTIR Analysis of CO Diffusion on Pt(997) Surface

Abstract

Using collision with energy-controlled rare gas atoms, the control and analysis of the diffusion of molecules on the surface was performed in an ultra high vacuum chamber with Fourier-transform infrared (FTIR) spectrometer and a supersonic molecular beam apparatus. A stepped Pt(997) surface was exposed to CO molecules and subsequently to energy-controlled Ne or Ar atoms. There was no change in the CO stretching mode region of the FTIR spectrum of the Pt(997) surface after Ne atoms having an average translational energy of 0.23 eV were collided with it. However, when Ne atoms having an average translational energy of 0.56 eV were collided with the surface, the intensity of the peak assigned to the CO stretching mode at terrace sites decreased, while that at step sites increased with increasing the exposure to the Ne atoms. This indicates that CO molecules adsorbed at the terrace sites migrate laterally to the step sites upon collision with high-energy Ne atoms. In addition, it was shown that the direction of diffusion can be controlled, the diffusion of the molecule in particular chemisorbed state can be activated, and the activation energy of diffusion can be estimated. A new method to examine the diffusion of adsorbates by the use of the collision with energy-controlled atoms is proposed.