Sticking probabilities in adsorption from liquid solutions: Alkylthiols on gold

The sticking probability, defined as the rate of adsorption per molecular collision with the surface, directly expresses the difficulty encountered by a molecule in scaling the barrier to adsorption. Its prior use has been restricted to adsorption of gases. A method extending this concept to adsorption from liquid solutions is applied to transient measurements of alkylthiol adsorption onto Sold from ethanol solutions. The initial sticking probability increases from similar to 10(-8) to similar to 10(-6) with alkyl chain length, implying a stabilization of the transition state by similar to 0.65 kJ/mol per CH2. Since their sticking probabilities in the gas phase are similar to 1.0, the solvent increases the activation free energy by similar to 40 kJ/mol.