Improved charge transfer multiplet method to simulateM- andL-edge X-ray absorption spectra of metal-centered excited states

Abstract

Charge transfer multiplet (CTM) theory is a computationally undemanding and highly mature method for simulating the soft X-ray spectra of first-row transition metal complexes. However, CTM theory has seldom been applied to the simulation of excited-state spectra. In this article, the CTM4XAS software package is extended to simulate M- and L-edge spectra for the excited states of first-row transition metals and also interpret CTM eigenfunctions in terms of Russell-Saunders term symbols. These new programs are used to reinterpret the recently reported excited-state M-edge difference spectra of photogenerated ferrocenium cations and to propose alternative assignments for the electronic state of these cations responsible for the spectroscopic features. These new programs were also used to model the L-edge spectra of Fe compounds during nuclear relaxation following photoinduced spin crossover and to propose spectroscopic signatures for their vibrationally hot states.

Photoinduced Valence Tautomerism of a Cobalt-Dioxolene Complex Revealed with Femtosecond M-Edge XANES

“…M-edge spectra of transition metal complexes are simulated using ligand field multiplet (LFM) theory. 29,30,32 Briefly, the metal center is modeled using a parametric Hamiltonian containing electron-nuclear and electron-electron coulomb terms, spin-orbit coupling and an electrostatic crystal field. Slater-Condon electron-electron repulsion and mixing parameters were reduced to 60-100% of their free ion values to account for electron delocalization.…”

“…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. [29][30][31][32] The development of ultrafast XUV light sources based on high-harmonic generation (HHG) has extended the applicability of M-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 31,33,34 and in transition metal oxide semiconductors, [35][36][37][38][39] but its applicability to molecular cobalt complexes has not yet been demonstrated.…”

Tracking the Metal-Centered Triplet in Photoinduced Spin Crossover of Fe(phen)32+ with Tabletop Femtosecond M-edge XANES

“…These results illustrate the utility and power of X-ray absorption near edge structure (XANES) spectroscopy at the Fe M2,3-edge, a technique that is sensitive to the oxidation state and spin-state of the metal center as well as the ligand field symmetry and strength. [11][12][13][14][15] Experimental XUV Transient Absorption: The XUV probe is produced by high harmonic generation using a tabletop instrument described previously. 11,16 Briefly, a Ti:sapphire driving laser (800 nm, 4 mJ, 35 fs, 1 kHz) is focused into a semi-infinite gas cell filled with 120 Torr of neon, where the intense electric field at the focal point generates a ~15 fs XUV pulse with a broad spectrum spanning 50 to 90 eV.…”

Tracking the Metal-Centered Triplet in Photoinduced Spin Crossover of Fe(phen)32+ with Tabletop Femtosecond M-edge XANES

“…These results illustrate the utility and power of X-ray absorption near edge structure (XANES) spectroscopy at the Fe M 2,3 -edge, a technique that is sensitive to the oxidation state and spinstate of the metal center as well as the ligand field symmetry and strength. [11][12][13][14][15] Kinetic slices at select energies are shown in Figure 2D, with the data shown as open symbols and fits with and without the 3 T intermediate (discussed below) shown as solid and dashed lines. Both the 57.0 eV peak and 54.5 eV shoulder show clear oscillations with a period of ~250 fs.…”