TEMPERATURE-CONTROLLED LASER-INDUCED POLYMERIZATION OF FORMALDEHYDE ON AG(111)

The UV-laser-induced polymerization of submonolayer formaldehyde on Ag(111) in UHV was investigated at temperatures between 35 and 85 K using electron energy loss spectroscopy. The yield of polymer decreases sharply as the sample temperature decreases, at approximately the same rate for H2CO as for D2CO. Below approximately 60 K, the photochemical initiation step of the polymerization process is still efficient, but the rate-determining, thermally controlled step cannot proceed, resulting in no observable polymer at these low temperatures. The initiator species is stable on the Ag(111) surface at 35 K; polymerization of formaldehyde can be induced long after UV irradiation at 35 K by heating the sample to above 65 K. The overall polymerization yield of formaldehyde on the surface can be controlled by varying the substrate temperature.