The sticking probability, defined as the rate of adsorption per molecular c
ollision with the surface, directly expresses the difficulty encountered by
a molecule in scaling the barrier to adsorption. Its prior use has been re
stricted to adsorption of gases. A method extending this concept to adsorpt
ion from liquid solutions is applied to transient measurements of alkylthio
l adsorption onto Sold from ethanol solutions. The initial sticking probabi
lity 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 0.6
5 kJ/mol per CH2. Since their sticking probabilities in the gas phase are s
imilar to 1.0, the solvent increases the activation free energy by similar
to 40 kJ/mol.