High Transient Mobility of Chlorine on ${\mathrm{TiO}}_2\left(110\right)$: Evidence for ``Cannon-Ball'' Trajectories of Hot Adsorbates

Scanning tunneling microscopy was used to study the initial stages of $\mathrm{Cl}{}_2$ adsorption on $\mathrm{TiO}{}_2\left(110\right)$. Cl atoms adsorb on the rows of fivefold coordinated surface Ti atoms, and mostly form well separated pairs (average distance $26Å$, atoms can be two or three rows apart). Abstractive adsorption results in 10% single Cl adatoms. We propose that $\mathrm{Cl}{}_2$ dissociates in an approximately upright position. The outer Cl atom is emitted along the bond axis and can surmount the substrate bridging oxygen rows in a “cannon-ball”-like trajectory. Channeling along the Ti rows leads to large average Cl-Cl distances.