The Journal of Physical Chemistry A最新文献

Continuous mixed valency involving Eu²⁺ and Eu³⁺ in Eu₄Bi₆Se₁₃ can be induced under applied pressure or at reduced temperatures. The monoclinic structure of Eu₄Bi₆Se₁₃, crystallizing in the P2₁/m space group (No. 11), features linear chains of Eu atoms aligned along the b-axis. Magnetic susceptibility measurements, conducted both parallel and perpendicular to the b-axis and analyzed using Curie-Weiss theory, alongside high-pressure partial fluorescence yield (PFY) data from X-ray absorption spectroscopy (XAS), indicate the material's propensity to adopt a mixed-valent state. Within this state, the trivalent Eu³⁺ configuration becomes increasingly favored as the pressure rises or the temperature decreases.

Despite decades of work on aqueous lead (Pb) adsorption on α-Fe₂O₃ (hematite) and α-Al₂O₃ (alumina), gaps between measurements and modeling obscure molecular-level understanding. Achieving well-matched geometries between theory and experiment for mineral-water interfaces is a hurdle, as surface functional group type and distribution must be accounted for in determining mechanisms. Additionally, computational methods that can describe the substrate are often not appropriate to capture aqueous effects. Progress requires focusing on well-studied and relevant systems, such as key facets (001), (012), and (110) of hematite and alumina, and ubiquitous contaminants such as aqueous Pb. In the past, bulk-parameterized bond-valence principles were used to rationalize Pb(II) adsorption trends. These approaches can break down at surfaces, where flexible bonding environments and adsorption-induced surface relaxations play a critical role. Here, we adapt and apply a density functional theory (DFT) and thermodynamics framework, integrating DFT-calculated energies with experimental data and electrochemical principles, to predict Pb(II) adsorption. Our model results capture trends across the full set of surfaces and predict that inner-sphere Pb(II) sorption on (001) alumina varies from unfavorable to weakly favorable across a range of pH conditions. This aligns with experimental insights that Pb(II) interacts at that surface through outer-sphere interactions. Extending to Fe(II) adsorption, we demonstrate a coverage-dependent site preference, potentially explaining disorder in overlayers grown by the oxidative adsorption of Fe(II) on hematite (001).

The key features of density-functional theory (DFT) within a minimalistic implementation of quantum electrodynamics are demonstrated, thus allowing to study elementary properties of quantum-electrodynamical density-functional theory (QEDFT). We primarily employ the quantum Rabi model that describes a two-level system coupled to a single photon mode and also discuss the Dicke model, where multiple two-level systems couple to the same photon mode. In these settings, the density variables of the system are the polarization and the displacement of the photon field. We give analytical expressions for the constrained-search functional and the exchange-correlation potential and compare them to established results from QEDFT. We further derive a form for the adiabatic connection that is almost explicit in the density variables, up to only a nonexplicit correlation term that gets bounded both analytically and numerically. This allows several key features of DFT to be studied without approximations.

Three new schemes of induced solvent charges for the auxiliary polarization formulation of the fragment molecular orbital method are proposed and compared to the original approach. It is found that the charge balance of the solute and solvent embeddings is crucial for maintaining a proper gap between occupied and virtual orbitals of fragments for zwitterionic systems in solution. The original instability is eliminated with the new scheme of fragment-specific solvent charges. The developed stable embedding method is applied to perform MP2/aug-cc-pVTZ calculations of a protein-ligand complex containing 1102 amino acid residues.

Gaining mechanistic insights into the structure-performance relationship connecting the donor and acceptor is essential to the rational design of high performance nonlinear optics (NLO) materials. Here, intramolecular boron/nitrogen (B/N)-locking strategies in combination with various electron-withdrawing groups, R (R = TXO, DPzS, TTR, DPyS, DTC, DSCZ, DMPS and TXO2), are proposed to address this issue. With the decreasing of torsion angles (θ₁ and θ₂) between donor (TPA) and acceptor (Py-Ph) units, the first hyperpolarizability (β) values are increased 45-65% and 4-27% by intramolecular B/N-locking strategies, respectively. Intriguingly, we also found some good linear correlations between θ₁, θ₂, and lgβ (where the determination coefficient R² ranges from 0.84 to 1.00). Meanwhile, between θ₁, θ₂, and the excited energy (ΔE) of the crucial excited state there have also good correlations, namely, the R² ranges from 0.80 to 1.00. As a result, given the fact of finding results, one can draw some meaningful insights, namely, intramolecular B/N-locking strategies hold good application perspective for enhancing β, and θ₁ and θ₂ can serve as effective descriptors in designing high-performance NLO materials based on the D-A architecture system.

Formaldehyde (HCHO) is an important intermediate in the breakdown of organic molecules in the atmosphere. It is the most abundant atmospheric carbonyl, and a major source of CO and H₂ upon degradation. Isotopic analysis offers valuable insights into molecular processes, deepening our understanding of atmospheric transformations. We present a model of the isotope-dependent photolytic isotopic fractionation of formaldehyde incorporating Rice-Ramsperger-Kassel-Marcus (RRKM) analysis, validate the model with new and pre-existing experimental data, and use it to describe photolytic kinetic isotope effects (KIEs) and their pressure dependencies. RRKM theory was used to calculate decomposition rates of the S₀, S₁, and T₁ states, using CCSD(T)/aug-cc-pVTZ, ωB97X-D/aug-cc-pVTZ, and CASPT2/aug-cc-pVTZ, respectively. We considered isotopologues HCHO, DCHO, DCDO, D¹³CHO, H¹³CHO, HCH¹⁷O, HCH¹⁸O, H¹³CH¹⁷O, and H¹³CH¹⁸O. We find that isotopic substitution notably affects the density of states, influencing rates of unimolecular decomposition and collisional energy transfer. Experimental photolysis rates ranged from $j_{HCHO}/j_{HC{H}^{18}O}$ = 1.027 ± 0.006 at 50 mbar to j_HCHO/j_DCDO = 1.418 ± 0.108 at 1000 mbar using a xenon lamp. The model accurately reproduced experimental pressure trends in KIEs, revealing that altitude-dependent deuterium enrichment in H₂ cannot be explained by pressure effects alone and must also consider wavelength dependence.

Rovibrational spectra of D₂O-CS₂ and HDO-CS₂ van der Waals complexes have been measured in the bending region of D₂O/HDO by direct absorption in a slit supersonic jet expansion. The H₂O-CS₂ dimer is reinvestigated in the bending region of H₂O with a higher rotational temperature compared with the previous study [Barclay, A. J. Phys. Chem. Chem. Phys. 2024, 26, 23053-23061], namely, ∼10 versus ∼2 K. Only the most stable isomer was observed, and precise molecular constants for these three complexes are determined. The HDO-CS₂ complex in the supersonic jet was relaxed into an equilibrated population. But the line intensities for transitions originating from the K_a = 1 levels in the ground state for both D₂O-CS₂ and H₂O-CS₂ are found to be significantly stronger than those predicted with normal nuclear spin statistical weights. This abnormality is likely due to the different yielding rates for the para- and ortho- spin species of D₂O-CS₂ or H₂O-CS₂ in the supersonic jet expansion.

In addition to harboring intense global magnetic fields, neutron stars also have outer envelopes that are subjected to high pressures. The outermost layer of a neutron star's envelope consists of a thin atmosphere, which in turn sits atop an ocean layer of condensed matter. The pressure at the topmost layer of the ocean is generally estimated to be around P ≳ 10³ GPa. The envelope is thought to be dynamic, with mixing between the layers, and this investigation seeks to delineate the energy landscape of neutral atoms from the atmosphere, which can get trapped inside denser surrounding material of the ocean layer below during mixing. The high-pressure environment is modeled as a quantum confined model by means of a spherical cavity using a piecewise potential (V_p) and a confining radius (R_C). A range of pressures and magnetic field strengths ($\sim 10^{6-9}$ T) are considered, and the two most astrophysically relevant atoms (hydrogen and helium) are studied herein, and, to the best of the author's knowledge, this is the first study to investigate the combination of the two effects in neutron star atmospheres. The energies of the first few low-lying states of each of hydrogen and helium atoms are computed (at the Hartree-Fock level of the theory for the latter), and the findings indicate that the binding energies of the states are considerably altered in such an environment. At the pressures relevant to the ocean layer (P ≳ 10³ GPa), it was found that the negative parity states of both hydrogen and helium do not survive as the energy shift introduced by the confinement is large enough to render them unbound. The positive parity states of these atoms do, however, survive at such pressures (albeit with somewhat lesser binding energies, for the case of helium) in neutron star envelopes. At lower pressures P ∼ 10² GPa, representing material in the lower reaches of the atmosphere though not at ocean layer depths, the energy landscape is still found to be appreciably altered for both the positive and the negative parity states of hydrogen and helium. Higher in the atmosphere, the energy shifts were found to diminish to negligible amounts for pressures relevant to the photosphere of the neutron star (P ∼ 10^-1 GPa). Overall, the study reveals that incorporating the effect of high pressure is important when studying the structure of atoms in the intense magnetic fields present in neutron star envelopes, as significant shifts in the computed energies will have bearing on any subsequent computations of oscillator strengths, transition wavelengths, as well as calculations of relative abundance of atoms and ions in atmosphere models. Thus, the results are relevant to understanding the spectra of neutron stars.

Mechanisms of photoinduced electron/energy transfer reversible addition-fragmentation chain transfer (PET-RAFT) polymerizations using zinc tetraphenylporphyrin (ZnTPP) or tetraphenylporphyrin (TPP) as photoredox catalysts (PCs) were studied using density functional theory calculations. To explain the selectivity of ZnTPP for trithiocarbonate compounds, the radical generation mechanisms of two chain transfer agents (CTAs), a trithiocarbonate (BTPA) and a dithiobenzoate (CPADB), were compared. The results suggest that the reaction mechanism (i.e., electron or energy transfer) depends on both the PC and CTA. For the most efficient combination, ZnTPP and BTPA, the reaction proceeds via an electron transfer mechanism. In contrast, TPP reacts with CPADB via an energy transfer mechanism. Furthermore, the formation of a stable complex between intermediates is identified for the reaction of ZnTPP and BTPA. These findings reveal the detailed mechanism and will offer insight into improving the yield and selectivity of PET-RAFT polymerization using porphyrins as PCs.

Singlet fission (SF) is a phenomenon that generates multiple excitons (triplets) on different chromophores from a single exciton (singlet) on one chromophore. Owing to the strong electronic correlation and a complicated excited state manifold of carotenoids (polyenes), the SF mechanism in carotenoids is different from acenes shown in J. Phys. Chem. Lett., 2022, 13, 6800-6805. However, the mechanism is expected to have significant effects of the geometry in the excited state and strong vibronic couplings between these low-lying excited states. Employing high-level state-of-the-art electronic structure methods, we show that the dark A_g states and charge transfer components play a major role in the SF process. The success of the process is strongly dependent on the relative orientation of the monomers. We have also shown that the high-frequency modes involving changes in bond length alternation are strongly coupled to the excited electronic states. These nuclear vibrational modes facilitate the SF process.