The Journal of Physical Chemistry A最新文献

In this work, we present the first derivation and implementation of analytic-gradient methods for the computation of the atomic axial tensors (AATs) required for simulations of vibrational circular dichroism (VCD) spectra using configuration interaction methods including double (CID) and single and double (CISD) excitations. Our new implementation includes the use of noncanonical perturbed orbitals to improve the numerical stability of the gradients in the presence of orbital near-degeneracies, as well as frozen-core capabilities. We validated our analytic CID and CISD formulations against two new finite-difference approaches. Using this new implementation, we investigated the significance of singly excited determinants and the role of CI-coefficient optimization in VCD simulations by comparisons among the Hartree–Fock (HF) theory, second-order Møller–Plesset perturbation (MP2) theory, CID, and CISD theories. For our molecular test set including (P)-hydrogen peroxide, (S)-methyloxirane, (R)-3-chloro-1-butene, (R)-4-methyl-2-oxetanone, and (M)-1,3-dimethylallene, we noted sign discrepancies between the HF and MP2 methods compared with that of the new CID and CISD methods for four of the five molecules as well as similar discrepancies between the CID and CISD methods for (M)-1,3-dimethylallene.

Water dimer is a classical example of an OH···O hydrogen bound complex and plays a critical role in the atmosphere. The bound OH-stretching (OH_b) fundamental transition displays the characteristic wavenumber redshift and intensity enhancement, observed repeatedly under many different experimental conditions. In contrast, the first OH_b-stretching overtone is predicted to be several orders of magnitude weaker in intensity. Recent full-dimensional ro-vibrational calculations have revised earlier theoretical predictions, suggesting that the OH_b-stretching first overtone may exhibit an intensity comparable to that of other observed OH-stretching transitions at these higher wavenumbers. Using jet expansion cavity ring-down spectroscopy in the predicted spectral region, we successfully observed this previously elusive transition. The observed transition wavenumber, intensity, and band shape show excellent agreement with the new theoretical predictions. The overlap of many closely lying ro-vibrational transitions, even at the cold temperature of the jet, gives rise to a relatively unstructured broad band. We determine the experimental OH_b-stretching first overtone vibrational band origin to be 7049 cm^–1 and estimate the lifetime to be about 10 ps.

Hot exciton materials have recently attracted attention for their potential to improve the efficiency of fluorescent organic light-emitting diodes (OLEDs) by harvesting triplet excitons through high-lying reverse intersystem crossing (hRISC). As internal conversion (IC) typically proceeds quite fast, an efficient hRISC pathway will be essential for the device performance. Vibronic coupling is one of the key mechanisms known to enhance RISC in conventional donor–acceptor type thermally activated delayed fluorescence (TADF) molecules. Motivated by this, we evaluate the vibronic correction of spin–orbit coupling (SOC) in 10′-diphenyl-9,9′-bianthracene (PPBA) and its derivatives using a first-order perturbative approach based on time-dependent density functional theory (TDDFT). Although the target states T₃ and S₁ are close in energy, their similar charge-transfer (CT) character results in negligibly small zeroth-order SOC, leading to intrinsically slow hRISC rates in all considered molecules. However, vibronic corrections significantly enhance SOC and increase the hRISC rate by nearly 4 orders of magnitude. At vibrationally distorted geometries, we observe partial mixing of CT and locally excited (LE) character in a nonidentical fashion between the two electronic states, thereby dynamically enhancing SOC. These findings demonstrate the importance of vibronic effects in hot exciton systems with flexible multiple-ring backbones and highlight the useful correction schemes in photophysical analyses of OLED materials.

We develop a two-level theory of the second-order nonlinear X-ray response beyond the electric-dipole approximation, deriving the leading quadrupolar correction originating from interference with the dipolar pathway at the amplitude level. A compact scaling law links the correction to weighted linear-response oscillator strengths, allowing parameter-free estimates across different core edges within the limits of the two-level description. For difference frequency resonant with the core transition, within the two-level description adopted here, the frequency dependence of the observable beyond-dipole correction is set by the electric dipole–quadrupole pathway through field gradients and is controlled by the dimensionless factor (ω₁ + ω₂)²/Ω₀² = (2r – 1)² with r = ω₁/Ω₀, while the underlying dipole–quadrupole interference occurs at the amplitude level and cancels in the isotropically averaged intensity, leaving a small positive quadratic correction whose magnitude is estimated from an isotropic linear-response oscillator-strength ratio. In particular, for a two-color scheme with ω₁ = 4Ω₀ and ω₂ = 3Ω₀, the quadrupolar contribution modifies the difference-frequency intensity by about 1.3% at the O K edge of CO and 5.5% at the S K edge of cysteine, consistent with the (2r – 1)² dependence and the growth of f⁽²⁾ with core energy. In liquids and gases, where the emitted difference-frequency field is strongly reabsorbed at the core edge, the relevant observable is the per-molecule nonlinear conversion efficiency obtained from orientationally averaged single-molecule emission. After isotropic averaging with linear polarizations, the dipole–quadrupole interference term vanishes by symmetry at the intensity level, so the observable correction arises solely from the surviving quadratic beyond-dipole contribution and follows a unified scaling. The same two-level structure carries over to sum-frequency generation with a reduced nondipole prefactor. The model targets molecules in the gas phase or solution and does not address oriented or crystalline systems. These results provide a practical rule for estimating beyond-dipole effects in second-order X-ray mixing and clarify when a dipole-only analysis becomes inadequate.

Methacrolein (MACR) and methyl vinyl ketone (MVK) are the coproducts of Criegee intermediates (CIs) from isoprene ozonolysis, and the reaction between them has potential importance in the atmospheric degradation of volatile organic compounds. This work investigates the reaction mechanism and kinetics of the smallest Criegee intermediate, CH₂OO, with MACR and MVK. 1,3-Cycloaddition of CH₂OO across the C═O double bond forms a secondary ozonide (SOZ), which may decompose to organic acids and carbonyl compounds. The lowest-energy-dissociation pathway for the SOZ involves the formation of a singlet biradical intermediate (BIR) by ring fission, followed by H-shift isomerization and dissociation to products. Master equation (ME) calculations show that the rate constants show a negative temperature effect in the temperature range of 200–500 K for the reaction of CH₂OO with MACR and MVK. The collisionally stabilized SOZ was found to be the main products at 300 K and atmospheric pressure, which tend to decompose to organic acids and carbonyl compounds at high temperatures and low pressures.

Understanding strongly correlated systems is essential for advancing quantum chemistry and materials science, yet conventional methods like Density Functional Theory (DFT) often fail to capture their complex electronic behavior. To address these limitations, we develop a hybrid quantum-classical framework that integrates Multiconfigurational Self-Consistent Field (MCSCF) with the Variational Quantum Eigensolver (VQE). Our initial benchmarks on water dissociation enabled the systematic optimization of key computational parameters, including ansatz selection, active space construction, and error mitigation. Building on this, we extend our approach to investigate the interactions between graphene analogues and water, demonstrating that our framework produces binding energies consistent with high-accuracy quantum methods. Furthermore, we apply this methodology to predict the binding energies of transition metals (Fe, Co, Ni) on both pristine and defective graphene analogues, revealing strong charge transfer effects and pronounced multireference character─phenomena often misrepresented by standard DFT. In contrast to many existing quantum algorithms that are constrained to small molecular systems, our framework achieves chemically accurate predictions for larger, strongly correlated systems such as metal–graphene complexes. This advancement highlights the capacity of hybrid quantum-classical approaches to address complex electronic interactions and demonstrates a practical route toward realizing quantum advantage for real-world materials applications in the Noisy Intermediate-Scale Quantum (NISQ) era.

We report a systematic investigation of the electronic structures and photodetachment dynamics of platinum bromide anions, PtBr_n^– (n = 2–5), using cryogenic anion photoelectron spectroscopy combined with quantum chemical calculations. High-resolution spectra acquired at 193 nm provide accurate adiabatic and vertical detachment energies (ADEs and VDEs), which show excellent agreement with theoretical values. The measured ADEs, corresponding to the electron affinities (EAs) of the neutral species, increase monotonically with increasing bromine coordination, establishing the superhalogen nature of these species. Notably, PtBr₅^– exhibits an unusually broad low energy feature in the photoelectron spectrum, attributed to resonant autodetachment. Complementary analyses–including natural population analysis (NPA), frontier molecular orbital (FMO) mapping, and charge density difference (CDD) visualization–reveal the orbital origins of the observed detachment channels and the associated charge redistribution. Bonding characteristics and relative stabilities are further assessed through fuzzy bond order (FBO) and natural adaptive orbital (NAdO) analyses. These findings provide a more comprehensive understanding of the electronic structures and bonding of platinum halides, offering insights relevant to the stability and ligand-exchange reactivity of transition metal superhalogens.

Enols, the tautomeric forms of carbonyl compounds, are considered to play key roles in the formation of prebiotic molecules in the interstellar medium. Herein, we investigated the possibility of nitrogen-containing molecules in cationic acetone enolization by measuring the infrared spectra of acetone-acetonitrile, acetone-acrylonitrile, and acetone-ammonia binary cationic complexes in the range of 2400–3800 cm^–1 using a vacuum ultraviolet photoionization and infrared dissociation (VUV-IR) scheme. To determine the structures of the complex isomers corresponding to the observed spectra, ab initio electronic structure calculations and infrared spectral simulations were employed. The results suggest that ammonia effectively catalyzes cationic acetone enolization, whereas acetonitrile and acrylonitrile do not exhibit observable catalytic activity in this process. Through reaction pathway searching and microcanonical rate constant calculations, the lack of catalytic activity in the nitrile-containing complexes stems from their low-energy lone-pair electrons and insufficient excess energy acquired during photoionization. These factors collectively hinder the key proton-transfer reaction underlying cationic acetone enolization. These findings provide insights into the multiscale regulatory mechanisms that control enolization pathways in interstellar chemistry.

Biofuels are an appealing alternative to augment conventional fossil fuels, given that traditional fossil fuels are finite in nature despite being the highest-consumed energy source. Furans have been studied as potential biofuels due to their renewability, high energy density, and ability to both blend with existing fossil fuels and serve as a stand-alone fuel. Although promising, more research efforts on the combustion of furan-based biofuels are needed. In this study, the oxidation of 2,3-dimethylfuran (2,3-DMF) initiated by O(³P) was investigated using vacuum-ultraviolet synchrotron radiation from the Advanced Light Source at the Lawrence Berkeley National Laboratory. The reaction was studied at 550 K and 7 Torr. Major reaction products include 3-methyl-3-buten-2-one, 4,5-dimethyl-3(2H)-furanone, and 3-methyl-4-oxo-2(Z)-pentenal, with 3-methyl-3-buten-2-one being the most abundant.

Low-lying valence states of the planar rhombic (D_2h) structure of Co₂O₂ have been computationally studied at density functional theory (DFT) levels, at the singles and doubles coupled-cluster level augmented with a perturbative treatment of the triples (CCSD(T)), at the complete active space self-consistent field (CASSCF) level, and at the second-order complete active space perturbation theory (CASPT2) level. Calculations at the DFT, CCSD(T), and CASSCF levels suggest that the ground state is a high-spin septet state, whereas the CASPT2 calculations yield a singlet ground state (¹A_g). The wave function of the CCSD(T) ground state (⁷B_2u) is dominated by one Slater determinant and is therefore well described using single-reference methods, whereas the configuration interaction coefficient (CI) of the reference determinant (C₀) of the ¹A_g state is only 0.519 at the CASSCF level. High-spin states are stabilized at the DFT level by increasing the amount of Hartree–Fock (HF) exchange in the functional. Static and dynamic correlation effects must be considered to obtain the correct ground state of Co₂O₂. DFT calculations of the magnetically induced current density (MICD) susceptibility of the ¹A_g state using the TPSSh functional show that the molecule sustains a strong diatropic ring current, which has significant contributions from both σ and π orbitals.