Reorientation kinetics of hydroxyl groups in anatase TiO₂

The reorientation kinetics of hydrogen in a variety of complexes in the anatase polymorph of TiO₂ was investigated by means of stress-induced dichroism. For the hydrogen-defect resulting in an O-H vibrational mode with a frequency of 3389 cm^-1, the energy barrier separating adjacent equivalent in-plane sites of hydrogen was determined to be independent of the isotope and equal to 0.74 ± 0.02 eV, whereas the attempt frequency was found to be (1.10 ± 0.20) × 10¹² and (0.75 ± 0.15) × 10¹² s^-1 for hydrogen and deuterium, respectively. The defect with vibrational modes at 3412 and 3417 cm^-1 previously assigned to isolated hydrogen did not reveal alignment under the stress up to room temperature, which indicates that the barrier of hydrogen motion is above 0.9 eV.