5 research outputs found
Density Functional Theory Assessment of Molecular Structures and Energies of Neutral and Anionic Al<sub><i>n</i></sub> (<i>n</i> = 2–10) Clusters
We report the results of a benchmarking
study on hybrid, hybrid-meta,
long-range-corrected, meta-generalized gradient approximation (meta-GGA),
and GGA density functional theory (DFT) methods for aluminum (Al)
clusters. A range of DFT functionals, such as B3LYP, B1B95, PBE0,
mPW1PW91, M06, M06-2X, ωB97X, ωB97XD, TPSSh, BLYP, PBE,
mPWPW91, M06-L, and TPSS, have been used to optimize the molecular
structures and calculate the vibrational frequencies and four energetic
parameters for neutral and anionic Al<sub><i>n</i></sub> (<i>n</i> = 2–10) clusters. The performances of
these functionals are assessed systematically by calculating the vertical
ionization energy for neutral Al clusters and the vertical electron
detachment energy for anionic Al clusters, along with the cohesive
energy and dissociation energy. The results are compared with the
available experimental and high-level ab initio calculated results.
The calculated results showed that the PBE0 and mPW1PW91 functionals
generally provide better results than the other functionals studied.
TPSS can be a good choice for the calculations of very large Al clusters.
On the other hand, the B3LYP, BLYP, and M06-L functionals are in poor
agreement with the available experimental and theoretical results.
The calculated results suggest that the hybrid DFT functionals like
B3LYP do not always provide better performance than GGA functionals
Time-Resolved X‑ray Spectroscopy in the Water Window: Elucidating Transient Valence Charge Distributions in an Aqueous Fe(II) Complex
Time-resolved
nitrogen-1s spectroscopy in the X-ray water window
is presented as a novel probe of metal–ligand interactions
and transient states in nitrogen-containing organic compounds. New
information on ironÂ(II) polypyridyl complexes via nitrogen core-level
transitions yields insight into the charge density of the photoinduced
high-spin state by comparing experimental results with time-dependent
density functional theory. In the transient high-spin state, the 3d
electrons of the metal center are more delocalized over the nearest-neighbor
nitrogen atoms despite increased bond lengths. Our findings point
to a strong coupling of electronic states with charge-transfer character,
facilitating the ultrafast intersystem crossing cascade in these systems.
The study also highlights the importance of local charge density measures
to complement chemical interaction concepts of charge donation and
back-bonding with molecular orbital descriptions of states
Electronic and Molecular Structure of the Transient Radical Photocatalyst Mn(CO)<sub>5</sub> and Its Parent Compound Mn<sub>2</sub>(CO)<sub>10</sub>
We present a time-resolved
X-ray spectroscopic study of the structural and electronic rearrangements
of the photocatalyst Mn<sub>2</sub>(CO)<sub>10</sub> upon photocleavage
of the metal–metal bond. Our study of the manganese K-edge
fine structure reveals details of both the molecular structure and
valence charge distribution of the photodissociated radical product.
Transient X-ray absorption spectra of the formation of the MnÂ(CO)<sub>5</sub> radical demonstrate surprisingly small structural modifications
between the parent molecule and the resulting two identical manganese
monomers. Small modifications of the local valence charge distribution
are decisive for the catalytic activity of the radical product. The
spectral changes reflect altered hybridization of metal-3d, metal-4p,
and ligand-2p orbitals, particularly loss of interligand interaction,
accompanied by the necessary spin transition due to radical formation.
The spectral changes in the manganese pre- and main-edge region are
well-reproduced by time-dependent density functional theory and <i>ab initio</i> multiple scattering calculations
Femtosecond Soft X-ray Spectroscopy of Solvated Transition-Metal Complexes: Deciphering the Interplay of Electronic and Structural Dynamics
We present the first implementation of femtosecond soft X-ray spectroscopy as an ultrafast direct probe of the excited-state valence orbitals in solution-phase molecules. This method is applied to photoinduced spin crossover of [Fe(tren(py)<sub>3</sub>)]<sup>2+</sup>, where the ultrafast spin-state conversion of the metal ion, initiated by metal-to-ligand charge-transfer excitation, is directly measured using the intrinsic spin-state selectivity of the soft X-ray L-edge transitions. Our results provide important experimental data concerning the mechanism of ultrafast spin-state conversion and subsequent electronic and structural dynamics, highlighting the potential of this technique to study ultrafast phenomena in the solution phase
Light-Induced Radical Formation and Isomerization of an Aromatic Thiol in Solution Followed by Time-Resolved X‑ray Absorption Spectroscopy at the Sulfur K‑Edge
We
applied time-resolved sulfur-1s absorption spectroscopy to a
model aromatic thiol system as a promising method for tracking chemical
reactions in solution. Sulfur-1s absorption spectroscopy allows tracking
multiple sulfur species with a time resolution of ∼70 ps at
synchrotron radiation facilities. Experimental transient spectra combined
with high-level electronic structure theory allow identification of
a radical and two thione isomers, which are generated upon illumination
with 267 nm radiation. Moreover, the regioselectivity of the thione
isomerization is explained by the resulting radical frontier orbitals.
This work demonstrates the usefulness and potential of time-resolved
sulfur-1s absorption spectroscopy for tracking multiple chemical reaction
pathways and transient products of sulfur-containing molecules in
solution