THz spectroscopy & THz EPR

THz Spectroscopy & THz Electron Paramagetic Resonance (EPR)

Electron paramagnetic resonance (EPR) provides unique information on the magnetic structure-function relationship of materials containing unpaired electron spins. Combining this method with coherent synchrotron radiation, THz-EPR detects EPR excitations over a very broad energy and magnetic field range in a single spectrometer.

• determine spin state energies and interaction parameters of electron spins in the THz/FIR range for transition metal ion and lanthanide complexes and materials (e.g. molecular magnets, spin-crossover materials, catalysts)
• investigate spin-phonon couplings
• study (magnetic) phase transitions

THz spectroscopy and EPR - Scientific Applications

Methods

IR Spectroscopy, Time-resolved absorption, Polarimetry, Reflectometry

Remote access

depends on experiment - please discuss with Instrument Scientist

BESSY II THz-EPR Setup

Motivation

Main science drivers are investigations in spin coupling energies of high-spin transition metal and rare earth ions. Spin coupling energies are sensitive probes of the electronic structure and determine magnetic properties of compounds with unpaired electron spins. The latter are highly desired pieces of information, as high-spin paramagnetic ions determine the function of many vital catalytic processes in proteins and synthetic complexes, as well as the properties of systems with large exchange couplings, e.g. single-molecule magnets (SMMs), energy materials or strongly correlated solids.

Frequency-Domain Fourier-Transform THz-EPR (FD-FT THz-EPR)

EPR is capable of providing unique information on magnetic structure-function relationships of materials containing unpaired electron spins. However, conventional single frequency EPR frequently fails in cases where spin transition energies exceed the quantum energy of the spectrometer (typically <4 cm^-1). Employing very short electron bunches (low-α), we have demonstrated that coherent synchrotron radiation (CSR) [1, 2]-based FD-FT THz-EPR [3] provides a unique tool to overcome this restriction. Our approach allows for EPR excitations over a broad energy (3 cm^-1 – 700 cm^-1) and magnetic field range (-12 T – +12 T) in a single spectrometer. FD-FT THz-EPR has been successfully applied to high-spin ions in SMMs [4], single-chain magnets (SCMs) [5], catalytically relevant integer and non-integer high-spin transition metal ion complexes [6, 7], as well as in proteins [8] and strongly correlated solid-state systems [9].

Remote access

Remote access & control available for mail-in samples, possibly also staff-assisted experiments upon request.

References

[1] M. Abo-Bakr, J. Feikes, K. Holldack, P. Kuske, W. B. Peatman, U. Schade, G. Wustefeld and H. W. Hubers
Brilliant, coherent far-infrared (THz) synchrotron radiation
Phys. Rev. Lett. 90 (9), 094801 (2003)

[2] K. Holldack, S. Khan, R. Mitzner and T. Quast
Femtosecond terahertz radiation from femtoslicing at BESSY
Phys. Rev. Lett. 96 (5), 054801 (2006)

 [3] A. Schnegg, J. Behrends, K. Lips, R. Bittl and K. Holldack
Frequency domain Fourier transform THz-EPR on single molecule magnets using coherent synchrotron radiation
Phys. Chem. Chem. Phys. 11 (31), 6820-6825 (2009)

 [4] J. Nehrkorn, J. Telser, K. Holldack, S. Stoll and A. Schnegg
Simulating Frequency-Domain Electron Paramagnetic Resonance: Bridging the Gap between Experiment and Magnetic Parameters for High-Spin Transition-Metal Ion Complexes
J. Phys. Chem. B 119 (43), 13816-13824 (2015)

 [5] J. Nehrkorn, A. Schnegg, K. Holldack and S. Stoll
General magnetic transition dipole moments for electron paramagnetic resonance
Phys. Rev. Lett. 114 (1), 010801 (2015)

[6] J. Nehrkorn, K. Holldack, R. Bittl and A. Schnegg
Recent progress in synchrotron-based frequency-domain Fourier-transform THz-EPR
J. Magn. Reson. 280, 10-19 (2017)

[7] M. Rams, A. Jochim, M. Bohme, T. Lohmiller, M. Ceglarska, M. M. Rams, A. Schnegg, W. Plass and C. Nather
Single-Chain Magnet Based on Cobalt(II) Thiocyanate as XXZ Spin Chain
Chem. Eur. J. 26 (13), 2765 (2020)

[8] M. Tarrago, C. Romelt, J. Nehrkorn, A. Schnegg, F. Neese, E. Bill and S. Ye
Experimental and Theoretical Evidence for an Unusual Almost Triply Degenerate Electronic Ground State of Ferrous Tetraphenylporphyrin
Inorg. Chem. 60 (7), 4966-4985 (2021)

 [9] J. C. Ott, E. A. Suturina, I. Kuprov, J. Nehrkorn, A. Schnegg, M. Enders and L. H. Gade
Observability of Paramagnetic NMR Signals at over 10 000 ppm Chemical Shifts
Angew. Chem. Int. Ed. 60 (42), 22856-22864 (2021)

[10] T. Lohmiller, C. J. Spyra, S. Dechert, S. Demeshko, E. Bill, A. Schnegg and F. Meyer
Antisymmetric Spin Exchange in a mu-1,2-Peroxodicopper(II) Complex with an Orthogonal Cu-O-O-Cu Arrangement and S = 1 Spin Ground State Characterized by THz-EPR
JACS Au 2 (5), 1134-1143 (2022)

[11] T. Al Said, D. Spinnato, K. Holldack, F. Neese, J. Cornella and A. Schnegg
Direct Determination of a Giant Zero-Field Splitting of 5422 cm⁻¹ in a Triplet Organobismuthinidene by Infrared Electron Paramagnetic Resonance
J. Am. Chem. Soc. 147 (1), 84-87 (2025)

 [12] M. C. Neben, N. Wegerich, T. A. Al Said, R. R. Thompson, S. Demeshko, K. Dollberg, I. Tkach, G. P. Van Trieste, 3rd, H. Verplancke, C. von Hanisch, M. C. Holthausen, D. C. Powers, A. Schnegg and S. Schneider
Transient Triplet Metallopnictinidenes M-Pn (M = Pd(II), Pt(II); Pn = P, As, Sb): Characterization and Dimerization
J. Am. Chem. Soc. 147 (6), 5330-5339 (2025)

 [13] W. Chen, N. Kochetov, T. Lohmiller, Q. Liu, L. Deng, A. Schnegg and S. Ye
A Spectroscopic Criterion for Identifying the Degree of Ground-Level Near-Degeneracy Derived from Effective Hamiltonian Analyses of Three-Coordinate Iron Complexes
JACS Au 5 (2), 1016-1030 (2025)