X-ray absorption spectroscopy at the L-edge of 3d transition metals is widely used for probing the valence electronic structure at the metal site via 2p–3d transitions. Assessing the information contained in L-edge absorption spectra requires systematic comparison of experiment and theory. We here investigate the Cr L-edge absorption spectrum of high-spin chromium acetylacetonate Cr^III(acac)₃ in solution. Using a transmission flatjet enables determining absolute absorption cross sections and spectra free from X-ray-induced sample damage. We address the challenges of measuring Cr L absorption edges spectrally close to the O K absorption edge of the solvent. We critically assess how experimental absorption cross sections can be used to extract information on the electronic structure of the studied system by comparing our results of this Cr^III (3d³) complex to our previous work on L-edge absorption cross sections of Mn^III(acac)₃ (3d⁴) and Mn^II(acac)₂ (3d⁵). Considering our experimental uncertainties, the most insightful experimental observable for this d³(Cr^III)–d⁴(Mn^III)–d⁵(Mn^II) series is the L-edge branching ratio, and we discuss it in comparison to semiempirical multiplet theory and ab initio restricted active space calculations. We further discuss and analyze trends in integrated absorption cross sections and correlate the spectral shapes with the local electronic structure at the metal sites.

中文翻译：

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含测量和计算的绝对吸收截面的溶液中Cr ^III（acac）_3的Cr L边X射线吸收光谱

3d过渡金属L边的X射线吸收光谱被广泛用于通过2p–3d过渡来探测金属位点的价电子结构。评估L边吸收光谱中包含的信息需要对实验和理论进行系统的比较。我们在这里研究高纺丝乙酰丙酮铬Cr ^III（acac）₃的Cr L-edge吸收光谱在解决方案中。使用透射式平板喷气发动机可以确定绝对的吸收截面和无X射线引起的样品损伤的光谱。我们解决了在光谱上靠近溶剂的OK吸收边缘测量Cr L吸收边缘的挑战。通过将我们对这种Cr ^III（3d ³）配合物的结果与我们先前对Mn ^III（L边）的L边吸收截面的研究结果进行比较，我们严格地评估了实验吸收截面如何可用于提取所研究系统的电子结构信息。acac）₃（3d ⁴）和Mn ^II（acac）₂（3d ⁵）。考虑到我们的实验不确定性，此d ³（Cr ^III）–d ⁴（Mn ^III）–d ⁵（Mn ^II）系列最能观察到的实验是L边分支比率，我们将其与半经验多重峰进行比较理论和从头开始限制活动空间的计算。我们将进一步讨论和分析集成吸收截面中的趋势，并将光谱形状与金属部位的局部电子结构相关联。