The polymerization of ethylene on surfaces sequentially dosed with TiCl4 and trimethylaluminum was studied by Fourier transform infrared spectroscopy. The polymer film was observed in situ as a function of time and under the influence of 254-nm cw radiation. The rate of polyethylene are strongly dependent on the order of dosing and the partial pressure of the reactants that demonstrated to occur through two seperate photochemical channels; gas-phase photolysis of the reactants and solid-phase chemical transformation of a noncatalytic thin film.