Dipole-dipole interactions among CH_3Cl molecules on Ru(001): Correlation between work function change and thermal desorption studies

摘要

Work function change measurements (#DELTA##PHI#) combined with temperature programmed desorption (TPD) were employed to study layer growth mechanism and the CH_3Cl dipole-dipole interactions on Ru(001), over the temperature range of 97 K-230 K. The activation energy for desorption (E_a) and the molecular dipole moment (#mu#) both decrease from 55.9 kJ/mol and 2.44 D, at the zero coverage limit, to 38.6 kJ/mol and 1.27 D, at one monolayer. This coverage dependence originates from strong dipolar lateral repulsion among neighbor CH_3Cl molecules. Using a model introduced by Maschhoff and Cowin (MC) [J. Chem. Phys. 101, 8138 (1994)], the isolated adsorbed molecule's dipole moment, #mu#_0 (2.35 D) and polarizability #alpha#(8.1 * 10~(-24) cm~3), were extracted from TPD data. These values agree very well with #mu#_0 (2.12 D) and #alpha#(9.2 * 10~(-24) cm~3) obtained from work function change measurements by employing the same MC model. The ability to simulate both TPD and work function change data over a wide coverage range within the framework of a single electrostatic model has been demonstrated. It enabled better understanding of fine details of surface dipolar interactions.