Substrate-mediated photodesorption from multilayers of CH₃I on TiO₂(110) at 90 K

The substrate-mediated photodesorption of CH₃I on TiO₂(110) for low fluence irradiation at 257 and 320 nm has been investigated using time-of-flight quadrupole mass spectrometry. The photodesorption of CH₃I in contact with TiO₂(110) results from resonant electron transfer from photoexcited TiO₂(110) to CH₃I, followed by an Antoniewicz-type desorption process. Overlayers of 2~4 monolayer (ML) suppress this resonant desorption process due to collisional interactions. For thick films (>5 ML), photoexcitation of the TiO₂(110) can lead to solvation of an electron ejected from the substrate into the film, which can then induce desorption of molecules from the surface of the film.