Shrinking the Synchrotron: Tabletop Extreme Ultraviolet Absorption of Transition-Metal Complexes

Abstract

We show that the electronic structure of molecular first-row transition-metal complexes can be reliably measured using tabletop high-harmonic XANES at the metal M2,3 edge. Extreme ultraviolet photons in the 50-70 eV energy range probe 3p → 3d transitions, with the same selection rules as soft X-ray L2,3-edge absorption (2p → 3d excitation). Absorption spectra of model complexes are sensitive to the electronic structure of the metal center, and ligand field multiplet simulations match the shapes and peak-to-peak spacings of the experimental spectra. This work establishes high-harmonic spectroscopy as a powerful tool for studying the electronic structure of molecular inorganic, bioinorganic, and organometallic compounds.

Sub-100 fs Intersystem Crossing to a Metal-Centered Triplet in Ni(II)OEP Observed with M-Edge XANES

“…The computational framework used in this work does not include 3p photoionization above the absorption edge, which causes this discrepancy at high energy. 18 The experimental NiO spectrum in in Figure 2B contains two main peaks at 66.8 and 69.9 eV. As in the case of NiOEP, the simulated spectrum is a good match for the experimental data.…”

“…Experimental and simulated M-edge XANES spectra of singlet NiOEP are shown in Figure 2A, with those of NiO in Figure 2B as an example of a triplet Ni II system. The spectra are shown after subtraction of a power-law background signal caused by photoionization of valence electrons; 18 the raw spectra are given in Figure S1. The experimental spectrum of NiOEP shows three major peaks centered at 68.2 eV, 73.4 eV, and 79.6 eV.…”

“…M-edge XANES measures transitions between the 3p and 3d orbitals of first-row transition metals, and we recently showed that it provides comparable element-, ligand field-, oxidation state-, and ligand field specificity to synchrotron-based L-and K-edge XANES. 18 This technique has been used recently to resolve ultrafast photophysics of heme model complex iron(III)tetraphenylporphyrin chloride 19 as well as carrier photophysics in metal oxide semiconductors such as α-Fe 2 O 3 , Co 3 O 4 , and NiO. [20][21][22][23][24]…”

Phase matching of noncollinear sum and difference frequency high harmonic generation above and below the critical ionization level

“…HHG is an ideal source for many applications, including nanoscale imaging [6], studies of nanoscale transport [7], ultrafast photoelectron spectroscopy [8][9][10][11][12], and element specific characterizations of ultrafast dynamics [13][14][15][16][17].…”

Competition Between Intersystem Crossing and Vibrational Cooling in Photoinduced Valence Tautomerism of a Cobalt-Dioxolene Complex Revealed with Femtosecond M-Edge XANES

“…The 3p → 3d dipole-allowed transitions lying between 30-100 eV contain information about the oxidation state, spin state, and coordination geometry of the metal center, and can be predictably reproduced using ligand-field multiplet (LFM) simulations. [28][29][30][31] The development of ultrafast XUV light sources based on high-harmonic generation (HHG) has extended the applicability of M 2,3 -edge spectroscopy to study the dynamics of 3d transition metal complexes. Femtosecond M-edge XANES has been used to measure excited-state relaxation dynamics in Fe and Ni complexes 30,32,33 and in transition metal oxide semiconductors, [34][35][36][37][38] but its applicability to molecular cobalt complexes has not yet been demonstrated.…”