Fig. 2: Observation of the oxygen exchange between H₂¹⁸O and α-Fe₂¹⁶O₃ by TPD and LEIS.

a TPD spectrum (1 K/s) after a dose of ≈1.9 H₂¹⁸O/u.c. at 120 K. The β peak is observed mostly in the m/e = 20 signal, while the γ peak desorbs in two channels of similar intensity, indicating substantial oxygen exchange with the α-Fe₂¹⁶O₃ substrate. b Oxygen exchange observed during 2.7 × 10⁻⁸ mbar H₂¹⁸O exposure at 350 K. Upon opening of the molecular beam shutter, roughly 1/3 of the signal is observed in the m/e = 18 channel. After ca. 360 s, almost all the signal is contained in the m/e = 20 channel due to the saturation of the surface with ¹⁸O. The overall water signal remains constant. c LEIS characterization (1 keV He⁺, scattering angle 90°) of the α-Fe₂¹⁶O₃ as prepared (top), after the H₂¹⁸O exposure as shown in b (middle) and after a single H₂¹⁸O TPD experiment (bottom). The latter two spectra show substantial enrichment of the α-Fe₂¹⁶O₃ surface with ¹⁸O. Source data are provided as a Source Data file.