Infrared absorption on hydrogen in anatase TiO 2

IR absorption study of natural single‐crystalline anatase TiO 2 has been performed. It was found that as‐received material reveals absorption lines at 3357.8, 3359.3, 3372.5, and 3389.3 cm −1 , whose intensity grows if the sample is hydrogenated from the H 2 ambient at 450 °C. In addition, hydrogenation results in the appearance of two lines at 3412.4 and 3416.9 cm −1 . Isotope substitution experiments have shown that all six lines are due to the stretch local vibrational modes (LVMs) of O–H bonds, which are preferentially aligned parallel to the c ‐axis of TiO 2 . The group of LVMs at 3357.8, 3359.3, 3372.5, and 3389.3 cm −1 retains the same relative intensities and is stable against thermal treatments up to 450 °C, whereas the hydrogen‐related complex(es) responsible for the 3412.4 and 3416.9 cm −1 lines disappear(s) after annealing at 250 °C. The nature of the defects resulting in these vibrational modes is discussed.