Studies of the effects of hydrogen bonding on monolayer structures of C18H37X (X = OH, SH) on HOPG

Based on Scanning tunneling microscopy (STM) observations of 1-C18H37X (X = OH, SH) adsorbed on HOPG, the hydrogen bonded complexes were studied using density functional theory (DFT) and molecular mechanics (MM). At, B3LYP/6- 31g and B3LYP/6-311g** levels, molecular dimers connected by hydrogen bond were obtained. The models of 1-C18H37X monolayer were optimized by consiste nt valence force field (CVFF), whose structures and interaction energies ag ree well with DFT calculations. It is noticed that due to the stronger hydr ogen bond interactions between C18H37OH molecules, C18H37OH adsorbed on HOP G shows only one kind of molecular arrangement, while C18H37SH exhibits two kinds of packing induced by alkyl-alkyl and adsorbate-substrate interactio ns. (C) 2001 Published by Elsevier Science B.V.