Experimental and theoretical STM imaging of xylene isomers on Pd „ 111 ...

We have performed a theoretical and experimental study of the three isomers of xylene, C6H4~CH3!2, adsorbed on Pd~111!. Using scanning tunneling microscopy ~STM!, we imaged the characteristic surface structures and investigated the molecular ordering for meta-, para-, and ortho-xylene adsorbed on Pd~111!. We used extended Hückel theory to predict the characteristic features of individual xylene molecules and to perform binding energy calculations for the preferred molecular orientations. STM observations of the surface features showed good agreement with the predictions, and the binding energy preferences correlated well with experiment.