  We have determined the electronic and atomic structure of N doped TiO2 using
a combination of hard x-ray photoelectron spectroscopy (HAXPES) and first-
principles density functional theory calculations. Our results reveal that N
doping of TiO2 leads to the formation of oxygen vacancies and the combination
of both N impurity and oxygen vacancies accounts for the observed visible light
catalytic behavior of N doped TiO2.
