The Journal of Physical Chemistry A最新文献

HF trimer, as the smallest and the lightest cyclic hydrogen-bonded (HB) cluster, has long been a favorite prototype system for spectroscopic and theoretical investigations of the structure, energetics, spectroscopy, and dynamics of hydrogen-bond networks. Recently, rigorous quantum 12D calculations of the coupled intra- and intermolecular vibrations of this fundamental HB trimer (J. Chem. Phys. 2023, 158, 234109) were performed, employing an older ab initio-based many-body potential energy surface (PES). While the theoretical results were found to be in reasonably good agreement with the available spectroscopic data, it was also evident that it is highly desirable to develop a more accurate 12D PES of HF trimer. Motivated by this, here we report a new, and the first fully ab initio 12D PES of this paradigmatic system. Approximately 42,540 geometries were sampled and calculated at the level of CCSD(T)-F12a/AVTZ. The permutationally invariant polynomial-neural network based Δ-machine learning approach (J. Phys. Chem. Lett. 2022, 13, 4729) was employed to perform cost-efficient calculations of the basis-set-superposition error (BSSE) correction. By strategically selecting data points, this approach facilitated the construction of a high-precision PES with BSSE correction, while requiring only a minimal number of BSSE value computations. The fitting error of the final PES is only 0.035 kcal/mol. To assess its performance, the 12D fully coupled quantum calculations of excited intra- and intermolecular vibrational states of HF trimer are carried out using the rigorous methodology developed by us earlier. The results are found to be in a significantly better agreement with the available spectroscopic data than those obtained with the previously existing semiempirical 12D PES.

Relative rate studies of the gas-phase reaction of amyl methacrylate, CH₂═C(CH₃)C(O)O[CH₂]₄CH₃, with ^•OH radicals were performed at (298 ± 2) K and 1000 mbar. The experiments were conducted in an atmospheric Pyrex chamber coupled to in situ Fourier transform infrared spectroscopy (FTIR). The rate coefficient obtained from the average of several experiments was k_AMMA+•OH = (8.10 ± 1.98) × 10^–11 cm³ molecule^–1 s^–1. Additionally, product studies were conducted under conditions similar to those of the kinetic experiments by using in situ FTIR spectroscopy. Pentanal, butanal, and hydroxyacetone were identified as the main reaction products. The initial pathway for the degradation of amyl methacrylate with ^•OH radicals occurs via addition of ^•OH to the >C═C< bond or hydrogen abstraction from the alkyl chain of the ester. The likelihood of hydrogen atom abstraction is 25%, while the addition of hydroxyl radicals to the double bond occurs with a probability of 75%. Based on these outcomes, a degradation mechanism is postulated. Furthermore, the atmospheric implications of the studied reaction were evaluated by estimating the tropospheric lifetime of amyl methacrylate toward ^•OH radicals as τ_OH = 3.43 h. Additionally, the Photochemical Ozone Creation Potential (POCP) of 84 was calculated for the reaction studied. Carbonyl compounds found as reaction products can exert a substantial influence on both air quality and public health.

Succinimide and its derivatives are cyclic five-membered rings that appear in a variety of natural products and are widely used in organic synthesis. From a structural standpoint, succinimide contains an NH group in the ring which interacts with two adjacent carbonyl groups, pushing the ring structure toward planarity at the expense of increasing ring strain and eclipsing interactions among the out-of-plane hydrogen atoms in the two CH₂ groups. Previous quantum chemical calculations at different levels of theory have predicted both a nonplanar C₂ structure and a planar C_2v structure, the latter of which is the most consistent with gas-phase electron diffraction measurements. Here, we report the pure rotational spectra of succinimide and N-chlorosuccinimide in the 26.5–40.0 GHz range using chirped-pulse Fourier transform microwave spectroscopy, supported by coupled cluster and density functional theory quantum chemical calculations. The spectra were fit to Watson’s A-reduced effective Hamiltonian, including both ³⁵Cl and ³⁷Cl isotopologues of N-chlorosuccinimide as well as the N and Cl quadrupole hyperfine interactions. On the basis of the agreement with quantum chemical calculations and the measured inertial defects, we find that the rotational spectra are consistent with a planar ring structure, with a maximum out-of-plane angle of ≤5°.

Density functional theory in conjunction with small core pseudopotentials and the associated basis sets was used to calculate potentials for multiple redox couples, covering a range of oxidation states for Ac (0 to III), Th (0 to IV), and Pa (0 to V) in aqueous solution. Solvation effects were incorporated using a supermolecule-continuum approach, with 30 water molecules representing two solvation shells, and the COSMO and SMD implicit solvation models. The calculated geometries for Ac(III), Th(IV), and Pa(V) were in reasonable agreement with the available experimental data. Using the COSMO model with the B3LYP functional, the calculated redox potentials were within ±0.2 V from experiment for most redox couples. Several pathways were explored for the Pa(V/IV) redox couple for different forms of Pa(V) and Pa(IV). Most Pa(V/IV) redox couples have very similar potentials, ranging from 0 to −0.4 V up to a pH of 1.4. At pH = 1.4, the potentials shift to values that are more negative than −0.7 V, reflecting the growing unfavorable nature of the redox process at higher pH levels. The calculated values for An(III/II) potentials were consistent with prior estimates and the available experimental data. The predicted redox potentials for An(II/I) were highly negative, as expected. For An(I/0) potentials, Th and Pa exhibited positive values, contrasting with the negative values calculated for Ac. The An^+m/An(0) potentials agreed better with the experimental data when using the COSMO solvation model as compared to the SMD model.

Modern computational chemistry methods are a useful tool for modeling many chemical systems, but they are challenged by multireference species (e.g., transition metals). A variety of diagnostics have been formulated to identify such cases. They are typically developed by analyzing multireference characters of small molecules, and many provide an average picture of the entire system. We caution the use of such diagnostics for large systems because large systems may include parts with varying degrees of multireference characters. Specifically, a small but highly multireference component may yield a large error in absolute terms, which may be masked in an average value over the entire molecule. As the calculation of molecular relative energies often concerns errors in absolute terms, such a false sense of safety may be detrimental. A prospective means to tackle this challenge is to use fractional occupation density to identify potentially problematic components in a system and then examine this moiety with higher-level computations on appropriately constructed smaller models.

Organic solid-state lasers have received increasing attention due to their great potential for realizing organic continuous-wave or electrically driven lasers. Moreover, they exhibit significant promise for optoelectronic devices due to their chemically tunable optoelectronic properties and cost-effective self-assembly traits. Recently, a great progress has been made in organic solid-state lasers via spatially separated charge injection and lasing. However, making directly electrically driven organic semiconductor lasers is very challenging. It is difficult because of a number of excitonic losses caused by the spin-forbidden nature as well as serious efficiency roll-off at a high current density. Here, a multifunction gain material, functioning both as a thermally activated delayed fluorescence (TADF) emitter with exceptional optical gain and as a source of phosphorescence, was theoretically investigated. The new molecule we designed exhibits a reduction of triplet accumulation through an effective exciton radiative process (5-fold boost in figure of merit) and significantly decreased exciton binding energy (dipole moment from 5.77 to 14.03 D), which benefit amplified spontaneous emission and lasing emission. Our work provides theoretical insights into organic solid-state lasers and may contribute to the development of new and efficient laser-gaining molecules.

To follow up on the unexpectedly good performance of several coupled-cluster models with approximate inclusion of 3-body clusters [Rishi, V.; Valeev, E. F. J. Chem. Phys. 2019, 151, 064102.] we performed a more complete assessment of the 3CC method [Feller, D. . J. Chem. Phys. 2008, 129, 204105.] for accurate computational thermochemistry in the standard HEAT framework. New spin-integrated implementation of the 3CC method applicable to closed- and open-shell systems utilizes a new automated toolchain for derivation, optimization, and evaluation of operator algebra in many-body electronic structure. We found that with a double-ζ basis set the 3CC correlation energies and their atomization energy contributions are almost always more accurate (with respect to the CCSDTQ reference) than the CCSDT model as well as the standard CCSD(T) model. The mean absolute errors in cc-pVDZ {3CC, CCSDT, and CCSD(T)} electronic (per valence electron) and atomization energies relative to the CCSDTQ reference for the HEAT data set [Tajti, A. . J. Chem. Phys. 2004, 121, 11599–11613.], were {24, 70, 122} μE_h/e and {0.46, 2.00, 2.58} kJ/mol, respectively. The mean absolute errors in the complete-basis-set limit {3CC, CCSDT, and CCSD(T)} atomization energies relative to the HEAT model reference, were {0.52, 2.00, and 1.07} kJ/mol, The significant and systematic reduction of the error by the 3CC method and its lower cost than CCSDT suggests it as a viable candidate for post-CCSD(T) thermochemistry applications, as well as the preferred alternative to CCSDT in general.

Understanding the structure and properties of heterocyclic radicals and their cations is crucial for elucidating reaction mechanisms as they serve as versatile synthetic intermediates. In this work, the N-carbazolyl radical 1 was generated via pyrolysis and characterized using photoion mass-selected threshold photoelectron spectroscopy coupled with tunable vacuum-ultraviolet synchrotron radiation. The N-centered radical 1 is classified as a π-radical (²B₁), with the unpaired electron found to be delocalized over the central five-membered ring of the carbazole. Adiabatic ionization energies corresponding to the transition from radical 1 to its singlet 1⁺(¹A₁) and triplet 1⁺(³B₂) cations were determined to be 7.70 ± 0.03 and 8.14 ± 0.03 eV, respectively. The antiaromatic nitrenium ion 1⁺ exhibits a singlet ground state with an experimental singlet–triplet energy gap (ΔE_S–T) of −0.44 eV (10.1 kcal/mol), in very good agreement with theory. N-centered radicals are found to have a higher ionization energy than their C-centered analogues due to stabilization of the singly occupied molecular orbital.

Over the course of the past several decades, spectroscopic surveys have unveiled the intricate nature of the aqueous chelation of Rare Earth Metals. Herein, we have collected a large data set about the interaction between 16 metal ions (Sc³⁺, Y³⁺, La³⁺, Ce³⁺, Pr³⁺, Nd³⁺, Sm³⁺, Eu³⁺, Gd³⁺, Tb³⁺, Dy³⁺, Ho³⁺, Er³⁺, Tm³⁺, Yb³⁺, and Lu³⁺) and perfluorinated nonsymmetric β-diketones, which contain chalcogen-bearing heterocyclic rings or aromatic moiety. The role and influence of the side ions on the chelation processes have been re-estimated to obtain revised stability constants. After analysis of more than 150 revised formation constants, a better periodic correlation has been shown. Scrutinizing the effects of the substituted group has revealed an “anti-Coulomb” behavior within the chalcogen group of diketones and a strictly electrostatic trend within the Rare Earth Metals series. Within the first-order approximation, the spin–orbit contribution to the Gibbs free energy of chelation has been estimated.

Calculation of transition temperatures T_1/2 for thermally driven spin-crossover in condensed phases is challenging, even with sophisticated state-of-the-art density functional approximations. The first issue is the accuracy of the adiabatic crossover energy difference ΔE_HL between the low- and high-spin states of the bistable metal–organic complexes. The other is the proper inclusion of entropic contributions to the Gibbs free energy from the electronic and vibrational degrees of freedom. We discuss the effects of treatments of both contributions upon the calculation of thermochemical properties for a set of 20 spin-crossover materials using a Hubbard-U correction obtained from a reference ensemble spin-state. The U values obtained from a simplest bimolecular representation may overcorrect, somewhat, the ΔE_HL values, hence giving somewhat excessive reduction of the T_1/2 results with respect to their U = 0 values in the crystalline phase. We discuss the origins of the discrepancies by analyzing different sources of uncertainties. By use of a first-coordination-sphere approximation and the assumption that vibrational contributions from the outermost atoms in a metal–organic complex are similar in both low- and high-spin states, we achieve T_1/2 results with the low-cost, widely used PBE generalized gradient density functional approximation comparable to those from the more costly, more sophisticated r²SCAN meta-generalized gradient approximation. The procedure is promising for use in high-throughput materials screening, because it combines rather low computational effort requirements with freedom from user manipulation of parameters.