The ultraviolet (UV) photon induced photodecomposition of 1,1,1-trifluoroacetone (TFA) adsorbed on the rutile TiO2(110) surface has been investigated with photon stimulated desorption (PSD) and thermal programmed desorption (TPD). TFA adsorbed on the reduced surface (8% oxygen vacancies) showed a molecular desorption peak at 260 K that shifts to 220 K with increasing TFA coverage, indicative of inter-adsorbate repulsion in the adsorbed layer. Adsorption of TFA on a reduced TiO2 surface pre-exposed to 20 L O2 leads to the formation of a TFA peak at 350 K accounting for 2/3rd ML coverage. A second peak at 250 K (1/3rd ML) completes the monolayer. Irradiation of the TFA covered oxidized surface by UV light at 90 K reduces the intensity of the 350 K TPD peak, with the 250 K state unaffected. Post-irradiation TPD shows evidence of the formation of small amounts of acetate (evolving as ketene at 650 K) as a surface bound decomposition product. UV irradiation of TFA causes the near complete photodecomposition of the photoactive species, leading to PSD of CH3, CF3, and CO during irradiation. This result is in contrast to the photochemical behavior of acetone, butanone and acetaldehyde on TiO2(110), where the gas phase ejection of only one of the two carbonyl substituent groups is observed and a stoichiometric amount of carboxylate is left on the surface. We conclude that fluorination alters the electronic structure of adsorbed carbonyls on TiO2(110) in such a way as to promote complete fragmentation of the adsorbed carbonyl complex.

  

(This work was supported by the DOE Office of Basic Energy Sciences, Division of Chemical Sciences and performed in the Environmental Molecular Sciences Laboratory at PNNL.)