Analyzing the Intensities of K-Edge Transitions in X Molecules (X = F, Cl, Br) for Use in Ligand K-Edge X-ray Absorption Spectroscopy.

Ligand K-edge X-ray absorption spectroscopy (XAS) is regularly used to determine the ligand contribution to metal-ligand bonds. For quantitative studies, the pre-edge transition intensities must be referenced to an intensity standard, and pre-edge intensities obtained from different ligand atoms cannot be compared without standardization due to different cross sections at each absorption edge. In this work, the intensities of the 1s → σ* transitions in F, Cl, and Br are analyzed for their use as references for ligand K-edge XAS. We show that the intensities of these transitions are equal to the intensities of the 1s → p transitions in the unbound halogens. This finding is supported by a comparison between the normalized experimental intensities for the molecules and the calculated oscillator strengths for the atoms. These results highlight the potential for these molecules to be used as intensity standards in F, Cl, and Br K-edge XAS experiments.