Dipole–dipole interactions among CH3Cl molecules on Ru(001): Correlation between work function change and thermal desorption studies

Abstract

Work function change measurements (ΔΦ) combined with temperature programmed desorption (TPD) were employed to study layer growth mechanism and the CH3Cl dipole–dipole interactions on Ru(001), over the temperature range of 97 K–230 K. The activation energy for desorption (Ea) and the molecular dipole moment (μ) 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 CH3Cl molecules. Using a model introduced by Maschhoff and Cowin (MC) [J. Chem. Phys. 101, 8138 (1994)], the isolated adsorbed molecule’s dipole moment, μ0 (2.35 D) and polarizability α(8.1×10−24 cm3), were extracted from TPD data. These values agree very well with μ0 (2.12 D) and α(9.2×10−24 cm3) 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.