Chromophore Analysis of Near-Edge X‑ray Absorption Spectra: Application to Four-Coordinate Phosphorus

• Published in: Journal of physical chemistry. C Vol. 128; no. 35; pp. 14750 - 14760
• Main Authors: East, Allan L. L., Pushie, M. Jake, Zhang, Nicole J.-Y., Sterenberg, Brian T.
• Format: Journal Article
• Language: English
• Published: American Chemical Society 05-09-2024
• Subjects: C: Spectroscopy and Dynamics of Nano, Hybrid, and Low-Dimensional Materials
• ISSN: 1932-7447; 1932-7455
• DOI: 10.1021/acs.jpcc.4c03887

This paper reports X-ray chromophore behavior: the substituents of an X-ray-absorbing atom (here phosphorus) were found to contribute consistent absorptions, in intensity and in relative peak position (transition energy). Linear relations for absolute peak position, as a function of the sum of the phosphorus neighbor-atom electronegativities (Σχ), have been found for ten chromophore peaks: P–F, P–O, P–Cl, P–N, P–CI, P–WI, P–CII(Ph), P–CII(pyr) P–CII(Fc), P–WII. The discovery was made by finding (i) surprisingly rich phosphorus K-edge X-ray absorption spectra [P X-ray absorption spectroscopy (XAS)] for several four-coordinate-phosphorus compounds, including four new ones involving the W­(CO)5 substituent, (ii) a vastly improved time-dependent (linear-response-based) density-functional-theory prediction method for P XAS which provides unprecedented XAS peak-assignment ability, and (iii) a fresh antibonding-orbital-based interpretive framework. The discovery, that selective X-ray excitation of substituents is possible, opens the door for studies of chemical reactivity implications (X-ray photochemistry), and improved studies of X-ray radiation exposure effects and damage.