7 research outputs found
Effect of Surface Passivation on Nanodiamond Crystallinity
Diamonds
approaching the nanoscale have the potential for use as
probe materials as their optical properties can be sensitive to optical/electric
fields, mechanical stress/pressure, and the configuration of nuclear
spins. The surface of nanodiamonds impacts their optical properties
and sensing capabilities, and examining the nanodiamond surface through
X-ray absorption can give insights into molecular surface structures.
Here, quantum dot models with varying amounts of surface carbon passivation
are prepared, optimized, and compared. The loss of the diamond sp<sup>3</sup> lattice is examined by investigating the bond length and
tetrahedral character of the carbons comprising nanodiamonds for the
appearance of aromatic sp<sup>2</sup> surface domains. Electronic
transitions in the carbon K-edge region, using the energy-specific
time-dependent density functional theory method, as well as vibrational
spectra are computed from the optimized models. The surface reorganization
is shown to affect the electronic characteristics of the nanodiamond.
As a result, there is a distinct absorption peak in the carbon K-edge
region, along with stretching modes in the vibrational spectra, that
can be correlated to the nature of the surface hybridization of the
nanodiamond
Robert F. Little, Class of 1898, joined the firm of White & Case in 1905, becoming one of its earliest associates. He left the firm in 1907 but returned in 1918, becoming a partner in 1921.
Robert F. Little joined the firm of White & Case in 1905, becoming one of its earliest associates. He left the firm in 1907 but returned in 1918, becoming a partner in 1921.https://digitalcommons.nyls.edu/firms/1003/thumbnail.jp
State Interaction Linear Response Time-Dependent Density Functional Theory with Perturbative Spin–Orbit Coupling: Benchmark and Perspectives
Spin–orbit coupling (SOC) is an important driving
force
in photochemistry. In this work, we develop a perturbative spin–orbit
coupling method within the linear response time-dependent density
function theory framework (TDDFT-SO). A full state interaction scheme,
including singlet–triplet and triplet–triplet coupling,
is introduced to describe not only the coupling between the ground
and excited states, but also between excited states with all couplings
between spin microstates. In addition, expressions to compute spectral
oscillator strengths are presented. Scalar relativity is included
variationally using the second-order Douglas-Kroll-Hess Hamiltonian,
and the TDDFT-SO method is validated against variational SOC relativistic
methods for atomic, diatomic, and transition metal complexes to determine
the range of applicability and potential limitations. To demonstrate
the robustness of TDDFT-SO for large-scale chemical systems, the UV–Vis
spectrum of Au25(SR)18– is computed and compared to experiment.
Perspectives on the limitation, accuracy, and capability of perturbative
TDDFT-SO are presented via analyses of benchmark calculations. Additionally,
an open-source Python software package (PyTDDFT-SO) is developed and released to interface with the Gaussian 16 quantum
chemistry software package to perform this calculation
State Interaction Linear Response Time-Dependent Density Functional Theory with Perturbative Spin–Orbit Coupling: Benchmark and Perspectives
Spin–orbit coupling (SOC) is an important driving
force
in photochemistry. In this work, we develop a perturbative spin–orbit
coupling method within the linear response time-dependent density
function theory framework (TDDFT-SO). A full state interaction scheme,
including singlet–triplet and triplet–triplet coupling,
is introduced to describe not only the coupling between the ground
and excited states, but also between excited states with all couplings
between spin microstates. In addition, expressions to compute spectral
oscillator strengths are presented. Scalar relativity is included
variationally using the second-order Douglas-Kroll-Hess Hamiltonian,
and the TDDFT-SO method is validated against variational SOC relativistic
methods for atomic, diatomic, and transition metal complexes to determine
the range of applicability and potential limitations. To demonstrate
the robustness of TDDFT-SO for large-scale chemical systems, the UV–Vis
spectrum of Au25(SR)18– is computed and compared to experiment.
Perspectives on the limitation, accuracy, and capability of perturbative
TDDFT-SO are presented via analyses of benchmark calculations. Additionally,
an open-source Python software package (PyTDDFT-SO) is developed and released to interface with the Gaussian 16 quantum
chemistry software package to perform this calculation
Unveiling Hidden Shake-Up Features in the Uranyl M<sub>4</sub>‑Edge Spectrum
The M4,5-edge high energy resolution X-ray
absorption
near-edge structure (HR-XANES) spectra of actinyls offer valuable
insights into the electronic structure and bonding properties of heavy-element
complexes. To conduct a comprehensive spectral analysis, it is essential
to employ computational methods that accurately account for relativistic
effects and electron correlation. In this work, we utilize variational
relativistic multireference configurational interaction methods to
compute and analyze the X-ray M4-edge absorption spectrum
of uranyl. By employing these advanced computational techniques, we
achieve excellent agreement between the calculated spectral features
and experimental observations. Moreover, the calculations unveil significant
shake-up features, which arise from the intricate interplay between
strongly correlated 3d core-electron and ligand excitations. This
research provides important theoretical insights into the spectral
characteristics of heavy-element complexes. Furthermore, it establishes
the foundation for utilizing M4,5-edge spectroscopy as
a means to investigate the chemical activities of such complexes.
By leveraging this technique, we can gain a deeper understanding of
the bonding behavior and reactivity of heavy-element compounds
Uranium-Mediated Peroxide Activation and a Precursor toward an Elusive Uranium <i>cis</i>-Dioxo Fleeting Intermediate
The activation of chalcogen–chalcogen bonds using
organometallic
uranium complexes has been well documented for S–S, Se–Se,
and Te–Te bonds. In stark contrast, reports concerning the
ability of a uranium complex to activate the O–O bond of an
organic peroxide are exceedingly rare. Herein, we describe the peroxide
O–O bond cleavage of 9,10-diphenylanthracene-9,10-endoperoxide
in nonaqueous media, mediated by a uranium(III) precursor [((Me,AdArO)3N)UIII(dme)] to generate a
stable uranium(V) bis-alkoxide complex, namely, [((Me,AdArO)3N)UV(DPAP)]. This reaction proceeds via
an isolable, alkoxide-bridged diuranium(IV/IV) species, implying that
the oxidative addition occurs in two sequential, single-electron oxidations
of the metal center, including rebound of a terminal oxygen radical.
This uranium(V) bis-alkoxide can then be reduced with KC8 to form a uranium(IV) complex, which upon exposure to UV light,
in solution, releases 9,10-diphenylanthracene to generate a cyclic
uranyl trimer through formal two-electron photooxidation. Analysis
of the mechanism of this photochemical oxidation via density functional
theory (DFT) calculations indicates that the formation of this uranyl
trimer occurs through a fleeting uranium cis-dioxo
intermediate. At room temperature, this cis-configured
dioxo species rapidly isomerizes to a more stable trans configuration through the release of one of the alkoxide ligands
from the complex, which then goes on to form the isolated uranyl trimer
complex
Uranium-Mediated Peroxide Activation and a Precursor toward an Elusive Uranium <i>cis</i>-Dioxo Fleeting Intermediate
The activation of chalcogen–chalcogen bonds using
organometallic
uranium complexes has been well documented for S–S, Se–Se,
and Te–Te bonds. In stark contrast, reports concerning the
ability of a uranium complex to activate the O–O bond of an
organic peroxide are exceedingly rare. Herein, we describe the peroxide
O–O bond cleavage of 9,10-diphenylanthracene-9,10-endoperoxide
in nonaqueous media, mediated by a uranium(III) precursor [((Me,AdArO)3N)UIII(dme)] to generate a
stable uranium(V) bis-alkoxide complex, namely, [((Me,AdArO)3N)UV(DPAP)]. This reaction proceeds via
an isolable, alkoxide-bridged diuranium(IV/IV) species, implying that
the oxidative addition occurs in two sequential, single-electron oxidations
of the metal center, including rebound of a terminal oxygen radical.
This uranium(V) bis-alkoxide can then be reduced with KC8 to form a uranium(IV) complex, which upon exposure to UV light,
in solution, releases 9,10-diphenylanthracene to generate a cyclic
uranyl trimer through formal two-electron photooxidation. Analysis
of the mechanism of this photochemical oxidation via density functional
theory (DFT) calculations indicates that the formation of this uranyl
trimer occurs through a fleeting uranium cis-dioxo
intermediate. At room temperature, this cis-configured
dioxo species rapidly isomerizes to a more stable trans configuration through the release of one of the alkoxide ligands
from the complex, which then goes on to form the isolated uranyl trimer
complex