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.