X-ray Induced Reorganization/Polymerization of Resorcinol on the TiO$_{2}$ Rutile (110) Surface

The room-temperature adsorption of resorcinol (1, 3 benzenediol, C$_{6}$H$_{4}$(OH)$_{2})$ on the (110) surface of rutile TiO$_{2}$ was investigated with STM and x-ray photoemission (XPS). The saturation coverage of resorcinol is smaller as compared to catechol (1,2 benzenediol) with a C1s/Ti2p$_{3/2}$ ratio of $\sim $ 7.3{\%} and 12{\%}, respectively. This indicates that resorcinol occupies on average more than two Ti sites on the surface. STM suggests that resorcinol molecules are mobile at lower coverage, whereas a weakly-ordered overlayer with a periodicity of 3 unit-cells along [001] is observed at higher coverages. Interestingly, exposure of resorcinol-saturated TiO$_{2}$ surface to an XPS Mg-K$\alpha $ beam (1253.6 eV) induces a reorganization of adsorbed resorcinol molecules. STM shows well-resolved double chains that run across [001]-oriented rows of TiO$_{2}$(110) surface. These results suggest that irradiation induces a polymerization reaction of adsorbed resorcinol molecules, where neighboring aromatic rings are arranged in a zig-zag configuration.