The Journal of Physical Chemistry A最新文献

The determination of three-dimensional structures (3D structures) is crucial for understanding the correlation between the structural attributes of materials and their functional performance. X-ray absorption near edge structure (XANES) is an indispensable tool to characterize the atomic-scale local 3D structure of the system. Here, we present an approach to simulate XANES based on a customized 3D graph neural network (3DGNN) model, XAS3Dabs, which takes directly the 3D structure of the system as input, and the inherent relation between the fine structure of spectrum and local geometry is considered during the model construction. It turns out to be faster than the traditional XANES fitting method when the simulation approach and XANES optimization algorithm are combined to fit the 3D structure of the given system. The geometric features of the system are included in the weighted message passing block of XAS3Dabs and their importance is investigated. XAS3Dabs model demonstrates superior accuracy in XANES prediction compared to most machine learning models. By extracting graphs constituted by edges related to the absorbing atom, our model reduces redundant information, thereby not only enhancing the model's performance but also improving its robustness across different hyperparameters. XAS3Dabs model can be generalized to simulate the spectra for the systems with the absorber having the designed absorption edge so as to meet the expectations of online data processing. The method is expected to be the key part of the online 3D structure analysis framework for the XAS-related beamlines of high-energy photon source (HEPS) now under construction.

Understanding how structural modifications affect the photophysics of organic linkers is crucial for their integration into metal-organic frameworks (MOFs) for light-driven applications. This study explores the impact of varying the amine functional group position on two terephthalic acid derivatives─linker 1 and linker 2─by investigating their photophysics through a combination of steady-state and ultrafast laser spectroscopy and time-dependent density functional theory (TD-DFT) calculations. With tetrahydrofuran as the solvent, time-correlated single-photon counting revealed a 2-fold increase in the S₁ excited-state lifetime of the molecule with the amine group at the meta position compared with that of the molecule with the amine group at the ortho position. This phenomenon can be attributed to restricted intramolecular twisting for the molecule with the amine group in the meta position. In this regime, an interplay of high-energy steric and conjugation barriers was revealed for the molecule with the amine group at the meta position by TD-DFT calculations. Moreover, femtosecond/nanosecond transient absorption spectroscopy revealed a reversible excited-state conformational change for the ortho isomer via intramolecular rotation that occurred within ∼110 ps, unlocking a triplet state manifold. This study underscores the importance of modifying organic emitters, either as free linkers or within MOFs, to increase their performance in sensing and light-emitting applications.

Vibronic coupling and multiple electronic states effect play a pivotal role in the molecular spectroscopy of large systems. Herein, we present a detailed theoretical study on the absorption (ABS) and electronic circular dichroism (ECD) spectra of three [7]helicene derivatives in chloroform, with a particular emphasis on the significance of vibronic coupling and the multiple electronic states effect in spectral simulations. The vertical gradient (VG) and vertical Hessian (VH) models, incorporating the Franck-Condon (FC) effect and Herzberg-Teller (HT) contribution, are considered in the vibronic calculations. The results indicate that the simulated vibrationally resolved spectra obtained by the VG model combined with the FC effect are more reliable, showing advantages in the rationality of spectral shapes, the accuracy of the relative heights of absorption peaks, and the correctness of positive and negative signals. Reliable predictions of the three [7]helicene derivatives allowed us to further explore the importance of the multiple electronic states effect in the vibrationally resolved spectra, demonstrating that the high-energy electronic excited states, particularly the fifth (S₅) and sixth (S₆) excited states, are essential for accurately capturing the fine structures observed in the experimental spectra. Our study predicts reliable theoretical reference spectra for the family of [7]helicene derivatives and provides a fundamental understanding of the vibronic coupling of chiral organic molecules with multiple electronic states.

Rate coefficients for ion-polar-molecule reactions between acetonitrile molecules (CH₃CN) and nitrogen molecular ions (N₂⁺), which are of importance to the upper atmospheric chemistry of Saturn's moon Titan, were measured for the first time at low translational temperatures. In the experiments, the reaction between sympathetically cooled N₂⁺ ions embedded in laser-cooled Ca⁺ Coulomb crystals and velocity-selected acetonitrile molecules generated using a wavy Stark velocity filter was studied to determine the reaction rate coefficients. Capture rate coefficients calculated by the Su-Chesnavich approach and by the perturbed rotational state theory considering the rotational state distribution of CH₃CN were compared to the experimental rate coefficients. The results indicate that the present reaction is barrierless and that the rate coefficients are consistent with the capture rate coefficients. The potential energy surface of the reaction product CH₃CN⁺ was calculated by the CCSD(T)/aug-cc-pVQZ level theory to explore possible isomerization and dissociation pathways. Several locally stable structures leading to H₂CCN⁺, HCCNH⁺, HCNCH⁺, and H₂CNC⁺ were found, while no intrinsic reaction coordinate leading to the CHCN⁺ formation pathway accompanied by H₂ abstraction has been identified. The H₂CCN⁺ + H dissociation channel is a major pathway of the reaction product, though theoretical calculations suggest the CHCN⁺ + H₂ dissociation channel is energetically feasible. The present experimental and theoretical studies will contribute to the accurate modeling of nitrile chemistry in interstellar matter and in the upper atmosphere of Titan.

The propensities for sigma hole bonding by halogen atoms bonded to central atoms below period 2 in the periodic table remain to be systematically examined. Using iodine as our reference halogen atom, a comprehensive analysis of the tendencies for halogen and other forms of significant sigma hole bonding by simple compounds of main group atoms from H to At is accomplished. An examination of the structure and bonding of complexes formed by those iodine-substituted main group compounds and sigma donating bases (ammonia and trimethylamine) is performed to probe the viability of halogen bonding by heavy main group R_nM-I compounds in particular, given the historic focus on period 2. We show that propensities for halogen bonding by F_nM-I systems for certain columns of the main group vary anomalously as M gets heavier due to a polarization-induced escalation of the electrostatic potential on I. In certain cases, the positive potential at the sigma hole on I is weaker than that at sigma holes on the central M or geminal R atoms. Previously unexplored cases of strong halogen bonding by the fluoroiodides of heavy group 13 atoms are identified, and prospects for other sigma hole type interactions to polarized (main group) central atoms are elucidated.

This study deals with the understanding of hydrogen atom scattering from graphene, a process critical for exploring C-H bond formation and energy transfer during atom surface collision. In our previous work [Shi, L.; J. Chem. Phys. 2023, 159, 194102], starting from a cell with 24 carbon atoms treated periodically, we have achieved quantum dynamics (QD) simulations with a reduced-dimensional model (15D) and a simulation in full dimensionality (75D). In the former work, the H atom attacked the top of a single C atom, enabling a comparison of QD simulation results to classical molecular dynamics (cMD). Our approach required the use of sophisticated techniques such as Monte Carlo canonical polyadic decomposition (MCCPD) and multilayer multiconfiguration time-dependent Hartree (ML-MCTDH), as well as further development of quantum flux calculations. We could benchmark our calculations by comparison to cMD calculations. We now refined our method to better mimic experimental conditions. Specifically, rather than sending the H atom to a specific position on the surface, we employed a plane wave for the H atom in directions parallel to the surface. Key findings for these new simulations include the identification of discrepancies between classical molecular dynamics (cMD) simulations and experiments, which are attributed to both the potential energy surface (PES) and quantum effects. Additionally, this study sheds light on the role of classical collective normal modes during collisions, providing insights into energy transfer processes. The results validate the robustness of our simulation methodologies and highlight the importance of considering quantum mechanical effects in the study of hydrogen-graphene interactions.

High-level multireference configuration interaction plus Davidson correction (MRCI + Q) calculation method was employed to determine the potential energy curves (PECs) of 10 Λ-S states, which come from the first and second dissociation channels of the SbP molecule, as well as 34 Ω states considering the spin-orbit coupling (SOC) effect. By solving the Schrödinger equation for nuclear motion, spectroscopic constants for the ground state X¹Σ⁺ and low-lying excited states were obtained and compared with experimental data. The excellent agreement indicates the reliability of our calculations. Additionally, the calculated spin-orbit (SO) matrix elements of the 1³Π and 1⁵Π states with other Λ-S states were analyzed, and the majority of the values in the Franck-Condon region exceed 200 cm^-1, indicating strong interactions between these states. What's more, the joint effects of spin-orbit coupling and avoided crossing were discussed in detail, leading to the complex potential energy curves and double-well phenomena observed in the Ω states. Taking forbidden transitions into account, transition dipole moments with the SOC effect are considered. The Franck-Condon factors, Einstein coefficients, and radiative lifetimes for the 1³Σ⁺₁ ↔ X¹Σ⁺₀₊ transition were obtained. Analysis indicates that direct laser cooling of SbP is inappropriate.

We present ab initio calculations of the resonant Auger spectrum of benzene. In the resonant process, Auger decay ensues following the excitation of a core-level electron to a virtual orbital. Hence, resonant Auger decay gives rise to higher-energy Auger electrons compared to nonresonant decay. We apply equation-of-motion coupled-cluster (EOM-CC) methods to compute the spectrum in order to explain the main features in the experimental spectrum and to assess the capability and limitations of the available theoretical approaches. The results indicate that participator decay can be well described with the Feshbach-Fano approach based on EOM-CC wave functions in the singles and doubles (SD) approximation, but spectator decay is more difficult to describe. This is because the target states of spectator decay are doubly excited, resulting in the need to include triple excitations in the EOM-CC wave function. Resonant Auger decay in benzene is thus a challenging test case for EOM-CC theory. We examine the performance of different noniterative triple corrections to EOM-IP-CCSD and our numerical results highlight the need to include triple excitations iteratively.

When dielectrics are hit with intense infrared (IR) laser pulses, transient metalization can occur. The initial attosecond dynamics behind this metallization are not entirely understood. Therefore, simulations are needed to understand this process and to help interpret experimental observations of it, such as with attosecond transient absorption (ATA). In this paper, we present first-principles simulations of ATA based on bulk-mimicking clusters and real-time time-dependent density functional theory (RT-TDDFT), with Koopmans-tuned range-separated hybrid functionals and Gaussian basis sets. Our method gives good agreement with the experiment for the breakdown threshold in silica and diamond. This breakdown voltage corresponds to a Keldysh parameter of approximately one and thus involves a transition to a regime where the dynamics are driven by tunneling. Pumping at an amplitude just below this value causes a mixture of multiphoton and tunneling excitations across the band gap to occur. The computed extreme ultraviolet and X-ray attosecond transient spectra also agree well with the experiment and show a decrease in optical density due to the transient population of the conduction band from the IR field. First-principles approaches such as this are valuable for interpreting the complicated modulations in a spectrum and for guiding future attosecond experiments on solids.

DNP (3,4-dinitropyrazole) has attracted much interest due to its promising melting characteristics and high detonation performances, such as low melting point, high density, high detonation velocity, and low sensitivity. In this work, first-principles molecular dynamics (MD) simulations were performed to investigate the anisotropic shock response of DNP in conjunction with the multiscale shock technique (MSST). The initial decomposition mechanism was revealed through the evolution of the chemical reaction and product analysis. Independent gradients based on the Hirshfeld partition (IGMH) method showed that van der Waals forces mainly exist between the layered structures. Chemical reaction analyses revealed four major initial decomposition reactions for the DNP molecule. At different shock velocities, the molecules in $\left(\overline{1}01\right)$ were more inclined to undergo H dissociation reactions, whereas the molecules in $\left(\overline{1}0\overline{1}\right)$ were more inclined to undergo nitro-dissociation reactions. Product analysis showed that the faster the shock velocities, the earlier the DNP molecules completely disappeared. Furthermore, N₂ and CO₂ were mainly produced by the ring-opening reaction, and their numbers in $\left(\overline{1}01\right)$ were higher than in $\left(\overline{1}0\overline{1}\right)$, indicating that the ring-opening reaction was more easy to occur in $\left(\overline{1}01\right)$. The ring-opening reaction mainly occurred in $\left(\overline{1}01\right)$, suggesting that $\left(\overline{1}01\right)$ was more decomposable than $\left(\overline{1}0\overline{1}\right)$. The fitting results of the state equation showed that the theoretical detonation pressures for $\left(\overline{1}01\right)$ and $\left(\overline{1}0\overline{1}\right)$ are close to the experimental value. These results could help to increase the understanding of shock-induced anisotropy in energetic materials.