Atomic chemisorption of chlorine on Ag(110) studied by high-resolution electron energy loss spectroscopy

We have studied atomic chemisorption at room temperature of chlorine on Ag(110) using high-resolution electron energy loss spectroscopy (HREELS), supplemented by XPS and LEED. The Cl-Ag vibration energy (around 25 meV) and the line-width of this loss peak show well resolved variations with both chlorine coverage and substrate temperature T. The observed shift with Tis related to the anharmonicity of the potential. Based on the Morse potential we derive an anharmonicity parameter chi(a)= 6.2 x 10(-2) for the (2 x 1)Cl-overlayer. This indicates that the anharmonicity is enhanced by about a factor of two as compared to the bulk. In contrast, we find chi(a)< 0.2 x 10(-2) for c(4 x 2)Cl. By comparison to other data we conclude that the (2 x 1)Cl-phase is a simple overlayer, with no significant reconstruction of the topmost substrate layer.