61 research outputs found
Magnetism and lattice dynamics of FeNCN compared to FeO
Three-dimensional non-oxidic extended frameworks offer the possibility to design novel materials with unique properties, which can be different from their oxide analogues. Here, we present first experimental results concerning unusual magnetic properties of FeNCN, investigated using Mössbauer spectroscopy and magnetometry between 5 and 380 K. This study reveals an unconventional behaviour of the magnetic parameters below the Néel temperature of 350 K, i.e., the hyperfine field on iron decreases with decreasing temperature. At room temperature, quadrupole and hyperfine magnetic field interaction energies are comparable in magnitude, which leads to a rare five-line absorption spectrum. We suggest that these features in the hyperfine field are caused by the combination of a small Fermi contact term and a temperature-dependent contribution from the orbital momentum and the dipole term. One additional spectral component is observed, which exhibits a magnetic relaxation behaviour and slows down at low temperatures to yield a sextet. The magnetometry data suggest that the antiferromagnetic FeNCN is rich in structural distortions, which results in a splitting of the field-cooled and zero-field-cooled curves. The lattice dynamics of FeNCN were investigated using nuclear inelastic scattering. The comparison of the obtained data with literature data of iron monoxide reveals very similar iron phonon modes with a small softening and a slightly reduced sound velocity
Proton Quantization and Vibrational Relaxation in Nonadiabatic Dynamics of Photoinduced Proton-Coupled Electron Transfer in a Solvated Phenol-Amine Complex
Nonadiabatic dynamics simulations
of photoinduced proton-coupled
electron transfer (PCET) in a phenol–amine complex in solution
were performed. The electronic potential energy surfaces were generated
on-the-fly with a hybrid quantum mechanical/molecular mechanical approach
that described the solute with a multiconfigurational method in a
bath of explicit solvent molecules. The transferring hydrogen nucleus
was represented as a quantum mechanical wave function calculated with
grid-based methods, and surface hopping trajectories were propagated
on the adiabatic electron–proton vibronic surfaces. Following
photoexcitation to the excited S<sub>1</sub> electronic state, the
overall decay to the ground vibronic state was found to be comprised
of relatively fast decay from a lower proton vibrational state of
S<sub>1</sub> to a highly excited proton vibrational state of the
ground S<sub>0</sub> electronic state, followed by vibrational relaxation
within the S<sub>0</sub> state. Proton transfer can occur either on
the highly excited proton vibrational states of S<sub>0</sub> due
to small environmental fluctuations that shift the delocalized vibrational
wave functions or on the low-energy proton vibrational states of S<sub>1</sub> due to solvent reorganization that alters the asymmetry of
the proton potential and reduces the proton transfer barrier. The
isotope effect arising from replacing the transferring hydrogen with
deuterium is predicted to be negligible because hydrogen and deuterium
behave similarly in both types of proton transfer processes. Although
an isotope effect could be observed for other systems, in general
the absence of an isotope effect does not imply the absence of proton
transfer in photoinduced PCET systems. This computational approach
is applicable to a wide range of other photoinduced PCET processes
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