The Journal of Physical Chemistry A最新文献

The first-stage acid-base equilibrium of 5,5,6-trihydroxy-6-methyldihydropyrimidine-2,4(1H,3H)-dione was studied for the first time in aqueous solutions. Its constant (pK_a1 = 9.23 ± 0.03) and thermodynamic parameters (ΔG₂₉₈ = 52 ± 1 kJ·mol^-1, ΔH = 83 ± 1 kJ·mol^-1, and ΔS₂₉₈ = 103 ± 4 J·mol^-1·K^-1) were determined by potentiometric titration. Computational analysis, including molecular dynamics (MD) simulations and quantum chemical calculations, was conducted to evaluate solvation effects and proton dissociation sites. MD simulations identified distinct solvation shells and interactions with water molecules, while quantum chemical calculations highlighted the primary deprotonation site. Fuzzy bond order (FBO) analysis and energy calculations of anionic forms corroborated these findings, demonstrating a strong correlation between the ΔE and FBO values. The research established the dissociation sequence for conformational R- and S-isomers of the title compound and validated the FBO method as an efficient tool for assessing dissociation processes in polybasic acids.

In both nature and industry, aerosol droplets contain complex mixtures of solutes, which in many cases include multiple inorganic components. Understanding the drying kinetics of these droplets and the impact on resultant particle morphology is essential for a variety of applications including improving inhalable drugs, mitigating disease transmission, and developing more accurate climate models. However, the previous literature has only focused on the relationship between drying kinetics and particle morphology for aerosol droplets containing a single nonvolatile component. Here we investigate the drying kinetics of NaCl-(NH₄)₂SO₄, NaCl-NH₄NO₃, and NaCl-CaCl₂ mixed salt aqueous aerosol droplets (25-35 μm radius) and the resulting morphology and composition of the dried microparticles. A comparative kinetics electrodynamic balance was used to measure evaporation profiles for each mixed salt aerosol at a range of relative humidities (RH) (0-50% RH); measurements of the evaporation kinetics are shown to be consistent with predictions from the "Single Aerosol Drying Kinetics and Trajectories" model. Populations of the mixed salt droplets were dried in a falling droplet column under different RH conditions and imaged using scanning electron microscopy to observe the impact of the drying kinetics on the morphology. Energy dispersive spectroscopy was used in tandem to obtain atomic maps and view the impact of drying kinetics on the composition of the resultant particles. It has been shown that the relationship between drying kinetics and dry particle morphology in mixed salt solution droplets is compositionally dependent and determined by the predominant salts that crystallize (i.e., (NH₄)₂SO₄, Na₂SO₄, or NaCl). The degree of homogeneity in composition throughout the particle microstructure is dependent on the drying rate.

A recruiting rate (k_rc) of 0.1-5 s^-1 has been proposed as the criterion for super-resolution spontaneously blinking rhodamines. Accurate prediction of the recruiting rate (k_rc) of rhodamines is very important for developing spontaneously blinking rhodamines. However, as far as we know, there is no reliable theoretical method to predict the k_rc. Herein, we meticulously investigated the effect of intermolecular hydrogen bonds on the spirocyclization reactions of rhodamines. Moreover, a theoretical descriptor (ΔE_C-T) was proposed to reliably assess the k_rc. ΔE_C-T quantified the ring-opening energy barrier of spirocyclization reactions. A robust linear correlation was established between theoretical ΔE_C-T values and experimentally k_rc values. Based on this correlation, we designed and screened five spontaneously blinking sulfonamide rhodamine dyes with optimized k_rc values. We expected that these findings could enable the targeted design of spontaneously blinking rhodamines.

The methoxy radical, CH₃O, has long been studied experimentally and theoretically by spectroscopists because it displays a weak Jahn-Teller effect in its electronic ground state, combined with a strong spin-orbit interaction. In this work, we report an extension of the measurement of the pure rotational spectrum of the radical in its vibrational ground state in the submillimeter-wave region (350-860 GHz). CH₃O was produced by H-abstraction from methanol using F atoms, and its spectrum was probed in absorption using an association of source-frequency modulation and Zeeman modulation spectroscopy. All the observed transitions together with available literature data in ν = 0 were combined and fit using an effective Hamiltonian allowing to reproduce the data at their experimental accuracy. The newly measured transitions involve significantly higher frequencies and rotational quantum numbers than those reported in the literature (f < 860 GHz and N ≤ 15 instead of 372 GHz and 7, respectively), which results in significant improvements in the spectroscopic parameters determination. The present model is well constrained and allows a reliable calculation of the rotational spectrum of the radical over the entire microwave to submillimeter-wave domain. It can be used with confidence for future searches of CH₃O in the laboratory and in the interstellar medium.

In this study, the radiative and nonradiative decay pathways from the first singlet excited states (denoted as S₁) of three bithiophene-fused isoquinolines were investigated by using the mixed-reference spin-flip time-dependent density functional theory approach. These isoquinolines, which are prepared via [2 + 2 + 2] cycloaddition reactions between three types of bithiophene-linked diynes and nitriles, exhibit different fluorescence quantum yields in response to the positions of their sulfur atoms. The decay processes, including the fluorescence emission and internal conversion, were considered. In the internal conversion pathway, the minimum energy conical intersection structures between the ground and first singlet excited states (denoted as S₀/S₁ MECI) of the ring strain for the isoquinoline skeleton and the ring opening of the thiophene skeleton were systematically explored. Dewar-type ring strain resulted in the smallest energy barrier from the equilibrium geometries of the ground state (denoted as S₀) to the MECI structures between the S₀ and S₁ states. The energy difference between the three types of bithiophene-fused isoquinolines at the transition state geometries of the S₁ state varies owing to the steric effects between the methyl groups and the hydrogen atom of the thiophene ring, and the excitation energy increases owing to a decrease in aromaticity. In addition, the oscillator strengths of the S₀ and S₁ states were evaluated at the equilibrium geometries of the S₁ state to determine the contribution of the fluorescence process. The obtained theoretical results are consistent with the experimental results.

We present a study of the cooperative nature of the forces dominating the interaction between gold atoms and aryl-aryl stacking. For this purpose, we modeled a series of complexes of the type dpm(AuR)₂ (dpm= bis(phoshino)methane; R = -C₆H₅, -C₆F₅, -C₆Cl₅, and -Cl). The models were calculated at the MP2, CCSD(T), and DFT-D3(BJ) (PBE and TPSS) levels of theory. The results show Au-Au and aryl-aryl stacking distances associated with noncovalent interactions. Also, the Wiberg indices, NBO, NCI, and QTAIM analyses exposed a low-density character between the gold atoms and aryl-aryl stacking, revealing that this contribution explains the stability of the complexes via dispersive interactions. Finally, the absorption spectra obtained are comparable with the experimental ones, and the orbitals obtained demonstrate that after the transitions, the orbitals are delocalized between the gold atoms and the vertex atoms of the molecules.

The information entropy based on the occupation numbers has been found to play a central role in a description of electron correlation within the density-matrix functional theory [i-DMFT, see Phys. Rev. Lett. 2022, 128, 013001]. In this article, the i-DMFT method is applied to predict potential energy curves, equilibrium bond lengths, and harmonic vibrational frequencies for the hydrogen halides: HF, HCl, and HBr. The results are compared with other theoretical calculations and experimental spectroscopic data.

The recent detection of benzonitrile (C₆H₅CN) in the interstellar medium is one of the most fascinating discoveries in astrochemistry and molecular astrophysics. However, the mechanism of its formation in interstellar ices remains unclear. Here, we report the first evidence for the direct synthesis of benzonitrile through the radiation-induced transformations of an isolated C₆H₆···HCN complex in inert rigid media at cryogenic temperature (4.5 K), as monitored by Fourier transform infrared (FTIR) spectroscopy. The complex was prepared in a solid krypton matrix and characterized by the experimentally observed complexation-induced shifts in the FTIR spectra on the basis of comparison with the results of ab initio calculations. The formation of benzonitrile was revealed through the observation of its three fundamentals and partially confirmed by experiments with deuterated benzene. Presumably, C₆H₅CN results from the dehydrogenation of complex excited states followed by prompt radical-radical recombination within the matrix cage. The proposed route may be relevant to the formation of C₆H₅CN both in the bulky astrophysical ices and on the surface of interstellar dust grains.

Aromaticity is one of the most classical concepts in the field of modern chemistry and has been employed to explain and design substances with special stability. Although the knowledge about Hückel's and Baird's rules has been well established, the understanding of Möbius aromaticity remains extremely limited. In this letter, by employing density functional theory (DFT) calculations, we demonstrated that the four-membered VIB transition metal (TM) carbide clusters possess a highly stable open-shell planar tetrameric structure and exhibit double Möbius aromaticity, which was evidenced by analyzing multiple aromaticity criteria, including the electronic, magnetic, and energetic indicators. Each cluster was characterized by four delocalized π electrons and four delocalized σ electrons, forming a novel class exhibiting double Möbius aromaticity. Intriguingly, the unexpected stability of these open-shell clusters was suggested to arise from the hybridization of d-p atomic orbitals, as revealed by analysis of the composition of delocalized orbitals. Our findings highlight the significance of hybridization between the d orbitals of transition metals and the p orbitals of main group elements in the creation of dual Möbius aromatic species, which offers new avenues for the design of single-molecule magnetic inorganic materials.

We report on the temperature-dependent reactions of the carbon-chain anions C₂^- and C₄^-, as well as the hydrocarbons C₂H^- and C₄H^- with H atoms in the temperature regime between 8 and 296 K. The experiments have been carried out in a temperature-variable radiofrequency multipole ion trap. From the measured kinetics, we have derived reaction rate coefficients that are constant for all considered systems in the measured temperature regime. For the C₂^-, C₄^-, and C₄H^- anions, the values are about a factor of 2 smaller than the Langevin capture rate coefficient, while for C₂H^-, the measured value agrees with the Langevin value. No theoretical calculations are available at present to explain this. All rate coefficients are in good agreement with previous measurements at room temperature.