Intrinsic defects of Ti${\mathrm{O}}_2$(110): Interaction with chemisorbed ${\mathrm{O}}_2$, ${\mathrm{H}}_2$, CO, and C${\mathrm{O}}_2$

The interaction of Ti${\mathrm{O}}_2$(110) with ${\mathrm{O}}_2$, ${\mathrm{H}}_2$, CO, and C${\mathrm{O}}_2$ was studied by means of low-energy electron diffraction, x-ray photoelectron spectroscopy, electron energy-loss spectroscopy, thermal desorption, electron paramagnetic resonance, and measurements of changes in surface conductivities, $\Delta \sigma$, and work functions, $\Delta \varphi$, for $300\le T\le 1000$ K with particular emphasis on surface reactions involving intrinsic surface defects $2{\mathrm{Ti}}^{3+}·V_O^{}{}_{}{}^{\mathrm{}(+)\mathrm{}}$. The defects are thermodynamically stable at high temperatures and act as donors and specific adsorption sites for ${\mathrm{H}}_2$ and CO. Surface and subsurface reactions involving ${\mathrm{O}}_2$, ${\mathrm{H}}_2$, CO, and C${\mathrm{O}}_2$ can be separated from each other by analyzing the $\Delta \sigma$ and $\Delta \varphi$ effects in a charge-transfer model, which takes into account surface and bulk electronic states in the band gap attributed to the different defects formed during the interaction.