The Journal of Physical Chemistry A最新文献

In this work, we present maps of the integrand of the exchange energy K(r₁,r₂) in terms of atomic contributions. This quantity helps to improve the understanding of this quantum correction in chemical bonding. With a set of covalent and noncovalent diatomic molecules, we show that it is possible to develop useful vocabularies for identifying regions where the exchange correction removes or adds electrons predicted by the classical Coulomb term. Applying the results to four halogen-bonded complexes, we prove that it is possible to gain a further understanding of the characteristics of the interaction between them and to offer a complete description of the anisotropy of the σ hole. The results are confirmed by molecular orbital, NBO, and SAPT(DFT) analyses and bode well for the use of K(r₁,r₂) in chemical bond analysis.

Large-scale implementation of NTO (5-nitro-1,2,4-triazol-3-one), an energetic material used in military applications, causes its discharge to the environment. Reduction of NTO with bacterial nitroreductase or iron-containing minerals results in the formation of ATO (5-amino-1,2,4-triazol-3-one), which is an important intermediate in the process of NTO degradation in the environment. ATO may be dissolved in surface water and groundwater due to its good water solubility. Many organic pollutants in surface water can be decomposed under the action of the hydroxyl radical, an important reactive oxygen species produced under sunlight irradiation. A detailed investigation of possible mechanisms for ATO decomposition in water induced by the hydroxyl radical as one of the pathways for ATO environmental degradation was performed by computational study at the PCM(Pauling)/M06-2X/6-311++G(d,p) level. Decomposition of ATO was found to be a multistep process that can begin with a hydrogen atom abstraction from ATO. Formed intermediates undergo further H atom abstraction, hydroxyl radical attachment to carbon atoms, and rupture of C-N bonds, leading to low-weight inorganic species such as nitrogen gas, ammonia, nitric acid, and carbon(IV) oxide. The calculated activation energy and exergonicity of the studied reactions support the contribution of hydroxyl radical to ATO degradation in the environment.

We studied the photophysical properties of substituted perylenes using time-dependent density functional theory (TDDFT) with Tamm-Dancoff Approximation (TDA). The TDA-TDDFT method allowed us to examine how luminescence activity alters by substituting halogens at different positions (bay, ortho, and peri) of perylenes. Substituting larger halogens like chlorine and bromine at the bay position significantly affects the planarity of the π-system in perylenes. Interestingly, bay-bromoperylene (P-bBr) showed pronounced spin-orbit coupling (SOC) between singlet and triplet excited states. The heavy atom effect (HAE) functioned efficiently with a distorted π-system and substantially enhanced the SOC in P-bBr. Therefore, a rapid intersystem crossing (ISC) is responsible for turning off the fluorescence of P-bBr. In contrast, bromine substitution other than the bay position (i.e., ortho- and peri-bromoperylenes (P-oBr and P-pBr), which maintained planarity), or substituting lighter elements like a methyl group (similar in size to Br) at the bay position of perylene did not substantially improve the SOC. Thus, the ISC is insufficient to quench the fluorescence in these systems. Additionally, substituting multiple bromines in perylene with at least one in the bay position (i.e., P-boBr₂, P-bpBr₂, and P-bopBr₃) further improved the SOC, leading to much faster ISC (10¹¹ s^-1) in P-bopBr₃. While multiple bromine substitutions other than the bay position (i.e., P-opBr₂) exhibited low ISC due to the planar π-system. So, the heavy bromine at the bay position of perylene causes significant enhancement of the ISC.

Recent advances in local electron correlation approaches have enabled the relatively routine access to CCSD(T) [that is, coupled cluster (CC) with single, double, and perturbative triple excitations] computations for molecules of a hundred or more atoms. Here, approaching their complete basis set (CBS) limit becomes more challenging due to extensive basis set superposition errors, often necessitating the use of large atomic orbital (AO) basis sets with diffuse functions. Here, we study a potential remedy in the form of non-atom-centered or floating orbitals (FOs). FOs are still rarely employed even for small molecules due to the practical complication of defining their position, number, exponents, etc. The most frequently used FO method thus simply places a single FO center with a large number of FOs toward the middle of noncovalent dimers; however, a single FO center for larger complexes can soon become insufficient. A recent alternative uses a grid of FO centers around the monomers with a single s function per center, which is currently applicable only for H, C, N, and O atoms. Here, we build on the above advantages and mitigate some drawbacks of previous FO approaches by using a layer of FO centers and 4-9 FOs/center for each monomer. Thus, a double layer of FOs is placed between the interacting subsystems. When extending the double-ζ AO basis with this double layer of FOs, the quality of conventional augmented double-ζ or conventional triple-ζ AO bases can be reached or surpassed with less orbitals, leading to few tenths of a kcal/mol basis set errors for medium-sized dimers. This good performance extends to larger molecules (shown here up to 72 atoms), as efficient local natural orbital (LNO) CCSD(T) computations with only double-ζ AO and 4 FOs/center FO bases match our LNO-CCSD(T)/CBS reference within ca. 0.1 kcal/mol. These developments introduce FO methods to the accurate modeling of large molecular complexes without limitations to atom types by further accelerating efficient correlation calculations, like LNO-CCSD(T).

The S(¹D) + D₂ → SD + D reaction is a prototype insertion chemical reaction that involves spin-orbit interactions in the exit channel. In this work, we report spin-orbit state-resolved differential cross sections (DCSs) of this reaction obtained by crossed beam experiments at collision energies of 266.2 and 206.5 cm^-1. The DCSs of specific rovibrational states exhibit a slight preference for forward scattering. When integrated over all rotational quantum states within each spin-orbit manifold, the total angular distributions of the two manifolds show nearly forward-backward symmetry, indicating that the deep well responsible for the long-living complex-forming mechanism predominates the entire reaction dynamics. Moreover, significant spin-orbit preference was observed at rotational quantum number N > 9 in the vibrationally ground state of SD products. It was also observed that SD products in the vibrationally excited state v' = 1 prefer to populate in the ²Π_3/2 manifold, with the ²Π_3/2/²Π_1/2 ratio of 15.8 and 25.2 at collision energies of 266.2 and 206.5 cm^-1, respectively. The experimental spin-orbit state-resolved DCSs obtained in this work will be of great importance for developing an accurate diabatic theory that includes spin-orbit interactions for this title reaction.

In natural aquatic environments, the fate of arsenic (As) is significantly influenced by redox processes involving iron (Fe) species. Understanding the mechanisms governing As transformation in the presence of Fe species is crucial for comprehending its environmental impact and advancing remediation strategies. In this work, the oxidation of As(III) in oxygenated Fe(II) solutions was investigated. Density functional theory (DFT) methods were employed to explore the reaction of Fe(II) with ³O₂ and subsequent As(III) oxidation by reactive species generated from Fe(II) oxidation. Electron paramagnetic resonance analysis was utilized to confirm the formation of reactive species in the solution. Based on these results, it is concluded that ¹O₂, ·O₂H, and Fe(IV) are the critical oxidants responsible for As(III) oxidation in oxygenated Fe(II) solutions under circumneutral conditions. ¹O₂ readily oxidizes As(III) by forming an arsenic superoxide AsO₅H₃. Interaction of As(III) with ·O₂H or Fe(IV) leads to As(IV), which is further oxidized to As(V) by ³O₂, Fe(III), and Fe(IV).

The presence of small organic molecules at airless icy bodies may be significant for prebiotic chemistry, yet uncertainties remain about their origin. Here, we consider the role of hyperthermal reactive ions in modifying the organic inventory of ice. We employ molecular dynamics using the ReaxFF formalism to simulate bombardment of carbon-bearing ice by hyperthermal water group molecules (H_xO, x = 0-2) with kinetic energy between 2 and 58 eV. Methanol is the dominant closed-shell organic product for a CH₄ clathrate irradiated at low dose by atomic oxygen. It is produced at yields as high as 10%, primarily by a novel hot-atom reaction mechanism, while radiolysis makes a secondary contribution. At high irradiation doses (≳1.4 × 10¹⁵ cm^-2), the composition is driven toward greater carbon oxidation states with formaldehyde being favored over methanol production. Other water group impactors are less efficient at inducing chemistry in the ice, and alternate clathrate guest species (CO, CO₂) are very robust against hydrogenation.

Characterization of carbohydrate structures using mass spectrometry is a challenging task. Understanding the dissociation mechanisms of carbohydrates in the gas phase is crucial for characterizing these structures through tandem mass spectrometry. In this study, we investigated the collision-induced dissociation (CID) of glucose, galactose, and mannose in their linear forms, as well as the linear forms of hexose at the reducing end of 1-6 linked disaccharides, using quantum chemistry calculations and tandem mass spectrometry. Our results suggest that the dehydration reaction in linear structures is unlikely to occur due to the significantly high reaction barrier compared to those of C═O migration and C-C bond cleavage. We demonstrate that the different intensities of the cross-ring fragments observed in the CID spectra can be explained by the different transition state energies of C═O migration and C2-C3, C3-C4, and C4-C5 bond cleavages, and the branching ratios of the cross-ring fragments are significantly different between glucose and galactose. The application of the cross-ring fragments to oligosaccharides reveals that the stereoisomers of glucose and galactose in oligosaccharides can be differentiated based on the relative intensities of the cross-ring fragments produced by the C2-C3 bond cleavage and C3-C4 bond cleavage, a differentiation that cannot be achieved by conventional tandem mass spectrometry.

Smog chamber experiments were conducted to establish the atmospheric chemistry of (E)- and (Z)-CF₃CF₂CH═CHCF₂CF₃. Kinetics of the reactions of the two compounds with Cl atoms and OH radicals were measured using relative rate techniques, giving k(Cl + (E)-CF₃CF₂CH═CHCF₂CF₃) = (5.63 ± 0.84) × 10^-12, k(Cl + (Z)-CF₃CF₂CH═CHCF₂CF₃) = (1.17 ± 0.20) × 10^-11, k(OH + (E)-CF₃CF₂CH═CHCF₂CF₃) = (1.64 ± 0.21) × 10^-13, and k(OH + (Z)-CF₃CF₂CH═CHCF₂CF₃) = (3.13 ± 0.38) × 10^-13 cm³ molecule^-1 s^-1 in 680 Torr air/N₂/O₂ diluents at 296 ± 2 K. Rate coefficients for the reactions with O₃, k(O₃ + (E)-CF₃CF₂CH═CHCF₂CF₃) ∼ 1 × 10^-22 and k(O₃ + (Z)-CF₃CF₂CH═CHCF₂CF₃) ≤ 5× 10^-24 cm³ molecule^-1 s^-1, were established using absolute techniques in a 680 Torr air diluent and 296 ± 2 K. The Cl reaction with (E)-CF₃CF₂CH═CHCF₂CF₃ gives CF₃CF₂CHClC(O)CF₂CF₃ as the sole oxidation product, whereas the reaction with (Z)-CF₃CF₂CH═CHCF₂CF₃ also gives rise to the formation of the (E)-isomer in minor yields. The reaction of OH radicals with CF₃CF₂CH═CHCF₂CF₃ gives CF₃CF₂CHO in a yield of 177 ± 17%. The main atmospheric fate of (E)- and (Z)-CF₃CF₂CH═CHCF₂CF₃ is the reaction with OH radicals, resulting in overall atmospheric lifetime estimates of 71 and 37 days, for (E)- and (Z)-CF₃CF₂CH═CHCF₂CF₃, respectively. The IR absorption cross sections are reported, and the global warming potentials of (E)- and (Z)-CF₃CF₂CH═CHCF₂CF₃ for the 20-, 100-, and 500-year time horizons are calculated to be 36, 10, and 3 for the (E)-isomer and 11, 3, and 1 for the (Z)-isomer, respectively. Atmospheric processing of (E)- and (Z)-CF₃CF₂CH═CHCF₂CF₃ is expected to yield CF₃CF₂COOH and CF₃COOH in yields of <10%. This study provides a comprehensive description of the atmospheric chemistry and fate of (E)- and (Z)-CF₃CF₂CH═CHCF₂CF₃.

This study employs a machine learning (ML) model using the Gaussian process regression algorithm to generate potential energy surfaces (PES) from density functional theory calculations, facilitating the investigation of photodissociation dynamics of nitroaromatic compounds, resulting in NO release. The experimentally observed trends in the slow-to-fast branching ratios of the NO moiety were captured by estimating the branching ratio between the two distinct reaction pathways, viz., roaming and oxaziridine mechanisms, calculated from molecular dynamics simulations performed on a reduced two-dimensional T₁ surface. The qualitative agreement between the calculated and experimental results suggests that the mechanism dictating NO release is primarily governed by the dynamics on the T₁ surface.