1 California Institute of Technology, Pasadena, California 91125, United States
2 Division of Chemistry and Chemical Engineering, California Institute of Technology, Pasadena, California 91125, United States
Under reducing conditions, rutile TiO2 develops O vacancies (VO) coupled to Ti3+ centers. It is favorable for H atoms to enter this system, either forming OH groups or occupying vacancy sites (denoted HO) that bond to two Ti next to the vacancy. OH defects are well documented by the presence of infrared modes at ~3300 cm‑1, while HO is relatively under investigated. We report the energies, geometries, and vibrational frequencies of hydrogen defects in rutile predicted from Quantum Mechanics calculations, focusing on the coexistence of OH and HO. We find that HO is more stable than OH by 1.42 eV, leading to an infrared mode at ~1200 cm‑1. Introducing a second H forms an OH bond with an infrared mode at ~3300 cm-1. These results suggest that assessments of the hydrogen storage in mantle phases of rutile and similar minerals based on OH bands may significantly underestimate H concentrations.