Radiation-induced conductivity in polymeric dielectrics can be significantly reduced by the incorporation of small-molecule traps (Kurtz and Arnold, JAP 57 (1985) 2532). In the appropriate concentration range, small molecules consisting of aromatic rings and strongly electron-withdrawing groups can reduce radiation-induced conductivity by more than 95 percent. Here, we investigate the doping of poly(ethylene terephthalate) films with several fluorenone dopants from solution. The dopant concentrations in the films, measured as a function of time and temperature, were fit by a combined adsorption-diffusion model that was solved analytically. Agreement between experimental data and the model is excellent, and physically meaningful parameters were obtained for all dopants under consideration, including the number of adsorption sites on the film, the equilibrium rate of adsorption, and the rate of diffusion. These parameters are also understood in the context of the chemical makeup of the dopants and the polymer.