  Defects in the surface region of a reducible oxide, as TiO2, have a profound
effect on applications, while their nature is very much influenced by the
possibility of small polaron formation. Here, we probe rutile (110) and anatase
(101) single crystals via high-resolution ultraviolet photoelectron
spectroscopy and resolve multiple components of the well-known defect state in
the band gap. In rutile, we find two at VBM+2.1 eV and VBM+1.4 eV, which we
assign to subsurface polaron traps and vacancy-bound states, respectively,
confirming the predicted partial suppression of polaron formation at high
vacancy concentration. New defects are created in situ on the anatase surface
by the synchrotron beam. We assign a component at VBM+2.3 eV, which can be
removed by annealing, to polaron states associated with surface oxygen
vacancies. We also identify a second component at VBM+1.6 eV, which can not be
removed by annealing, and is too deep to be associated with oxygen vacancies.
