Rossi T C, Grolimund D, Cannelli O, Mancini G F, Bacellar C, Kinschel D, Rouxel J R, Ohannessian N, Pergolesi D, Chergui M
Laboratory of Ultrafast Spectroscopy, Ecole Polytechnique Fédérale de Lausanne SB-ISIC-LSU and Lausanne Centre for Ultrafast Science (LACUS), CH-1015 Lausanne, Switzerland.
Laboratory for Femtochemistry - MicroXAS Beamline Project, Paul Scherrer Institute, CH-5232 Villigen, Switzerland.
J Synchrotron Radiat. 2020 Mar 1;27(Pt 2):425-435. doi: 10.1107/S160057752000051X. Epub 2020 Feb 14.
X-ray absorption linear dichroism of rutile TiO at the Ti K-edge provides information about the electronic states involved in the pre-edge transitions. Here, linear dichroism with high energy resolution is analyzed in combination with ab initio finite difference method calculations and spherical tensor analysis. It provides an assignment of the three pre-edge peaks beyond the octahedral crystal field splitting approximation and estimates the spatial extension of the corresponding final states. It is then discussed for the first time the X-ray absorption (XAS) of pentacoordinated titanium atoms due to oxygen vacancies and it is found that, similarly to anatase TiO, rutile is expected to exhibit a transition on the low-energy side of peak A3. Its apparent absence in the experiment is related to the degree of p-d orbital mixing which is small in rutile due to its centrosymmetric point group. A recent XAS linear dichroism study on anatase TiO single crystals has shown that peak A2 has an intrinsic origin and is due to a quadrupolar transition to the 3d energy levels. In rutile, due to its centrosymmetric point group, the corresponding peak A2 has a small dipole moment explaining the weak transition. The results are confronted with recent picosecond X-ray absorption spectroscopy on rutile TiO nanoparticles.
金红石型TiO₂在Ti K边的X射线吸收线性二色性提供了有关前边缘跃迁中涉及的电子态的信息。在此，结合从头算有限差分法计算和球张量分析，对具有高能量分辨率的线性二色性进行了分析。它给出了超越八面体晶体场分裂近似的三个前边缘峰的归属，并估计了相应末态的空间扩展。然后首次讨论了由于氧空位导致的五配位钛原子的X射线吸收（XAS），并且发现，与锐钛矿型TiO₂类似，金红石型预计在峰A3的低能侧会出现一个跃迁。实验中其明显缺失与p-d轨道混合程度有关，由于其中心对称点群，金红石型中的p-d轨道混合程度较小。最近对锐钛矿型TiO₂单晶的XAS线性二色性研究表明，峰A2有其内在起源，是由于向3d能级的四极跃迁。在金红石型中，由于其中心对称点群，相应的峰A2偶极矩较小，这解释了跃迁较弱的原因。将这些结果与最近对金红石型TiO₂纳米颗粒的皮秒X射线吸收光谱进行了对比。
