The Journal of Physical Chemistry A最新文献

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.

We report on new donor-chromophore-acceptor triads BDX-ANI-NDI and BDX-ANI-xy-NDI where the BDX donor is 2,2,6,6-tetramethylbenzo[1,2-d;4,5-d]bis[1,3]dioxole, the ANI chromophore is 4-(N-piperidinyl)naphthalene-1,8-dicarboximide, the NDI acceptor is naphthalene-1,8:4,5-bis(dicarboximide), and xy is a 2,5-xylyl spacer. The results on these compounds are compared to the analogous derivatives having a p-methoxyaniline (MeOAn) as the donor. BDX^•+ has no nitrogen atoms and only a single hydrogen atom coupled to its unpaired electron spin, and therefore has significantly decreased hyperfine interactions compared to MeOAn^•+. We use femtosecond transient absorption (fsTA) and nanosecond TA (nsTA) spectroscopies, the latter with an applied static magnetic field, to study the charge transfer dynamics and determine the spin-spin exchange interaction (J) for BDX^•+-ANI-NDI^•- and BDX^•+-ANI-xy-NDI^•- at both ambient and cryogenic temperatures. Time-resolved electron paramagnetic resonance (EPR) and pulse-EPR measurements on these spin-correlated radical pairs (SCRPs) were used to probe their spin dynamics. We demonstrate that BDX^•+-ANI-xy-NDI^•- has an unusually long lifetime of ∼550 μs in glassy butyronitrile (PrCN) at 85 K, which makes it useful for pulse-EPR studies that target quantum information science (QIS) applications. We also show that rotation of the BDX group about the single bond linking it to the neighboring phenyl group has a significant impact on the spin dynamics, and in particular the magnitude of J. By comparing the results on these compounds to the analogous MeOAn series, insights into design principles for creating improved spin-correlated radical pair systems for QIS studies are obtained.

Selected molecular species containing the disulfide bond, RSSR, have been considered, these ranging from hydrogen disulfide, H₂S₂ (R = H), to diphenyl disulfide with R = C₆H₅. The aim of this work is two-fold: (i) to investigate different computational approaches in order to derive accurate equilibrium structures at an affordable cost, (ii) to employ the results from the first goal in order to benchmark cheaper methodologies rooted in the density functional theory. Among the strategies used for the accurate geometrical determinations, the semiexperimental approach has been exploited in combination with a reduced-dimensionality VPT2 model, without however obtaining satisfactory results. Instead, the so-called "Lego brick" approach turned out to be very effective despite the flexibility of the systems investigated. Concerning the second target of this work, the focus was mainly on the S-S bond and the structural parameters related to it. Among those tested, PBE0(-D3BJ), M06-2X(-D3) and DSD-PBEP86-D3BJ have been found to be the best-performing functionals.

It has been reported that the self-assembly pattern of light levitating droplet clusters above the hot gas-liquid interface is dependent on the quantity of droplets. However, the already-reported theoretical explanation of the quantity-dependent self-assembly pattern cannot work well when the quantity of the light levitating droplet exceeds 15. Herein, we propose a new theoretical perspective to understand the self-assembly of a light levitating droplet cluster by referring to the classical densest packing problem of identical rigid circles in a larger circle with the introduction of the minimum total potential energy principle. Amazingly, the theoretical results obtained by this new approach agree well with experimental results, even though the quantity of the light levitating droplet is up to 142. This study deepens our understanding of the quantity-dependent self-assembly pattern of the light levitating droplet clusters and provides significant inspiration for other analogous self-assembly phenomena.

Organosulfates (OS, ROSO₃^-), ubiquitous constituents of atmospheric particulate matter (PM), influence both the physicochemical and climatic properties of PM. Although the formation pathways of OS have been extensively researched, only a few studies have investigated the atmospheric fate of this class of compounds. Here, to better understand the reactivity and transformation of OS under cloudwater- and aerosol-relevant conditions, we investigate the hydroxyl radical (OH) oxidation bimolecular rate constants (k_OS+OH^II) and products of five atmospherically relevant OS as a function of pH and ionic strength: methyl sulfate (MeS), ethyl sulfate (EtS), propyl sulfate (PrS), hydroxyacetone sulfate (HaS) and phenyl sulfate (PhS). Our results show that OS are oxidized by OH with k_OS+OH^II between 10⁸ - 10⁹ M^-1 s^-1, which corresponds to atmospheric lifetimes of minutes in aqueous aerosol to days in cloudwater. We find that k_OS+OH^II increases with carbon chain length (MeS < EtS < PrS) and aromaticity (PrS < PhS), but does not depend on solution pH (2, 9). In addition, we find that whereas the OH reactivity of the aliphatic OS studied here decreases by ∼2× with increasing ionic strength (0-15 M), the reactivity of PhS decreases by ∼10×. The oxidation of EtS and PrS produced organic peroxides (ROOH) as first-generation oxidation products, which subsequently photolyzed; the oxidation of PhS resulted in hydroxylated aromatic products. These results highlight the need for inclusion of OS loss pathways in atmospheric models, and suggest caution in using ambient OS concentration measurements alone to estimate their production rates.

In this work, effects of ozone (O₃) addition on ethylene-oxygen (C₂H₄-O₂) mixtures are computationally studied through the explosion limit profiles. The results show that the addition of minute quantities of ozone (with a mole fraction of 0.06% in the oxidizer) shifts the explosion limit of the C₂H₄-O₃-O₂ mixtures to the low-temperature regime. Further increases in the ozone concentration gradually strengthen the negative temperature coefficient (NTC) behavior at the second limit. That is because the explosion limit is primarily controlled by the ethylene ozonolysis reaction, and both the sensitivity analysis and chemical reaction rate perturbation method reveal specific kinetic reasons. Furthermore, it is shown that with the increasing equivalence ratio, the explosion limit curve with minute ozone addition rotates counterclockwise around a crossover point, while the explosion limit curve becomes complicated and the NTC behavior appears on the second limit with larger quantities of ozone addition. Furthermore, the effects of dilutions of nitrogen (N₂), argon (Ar), carbon dioxide (CO₂), and water (H₂O) on the explosion limits are also studied. To elucidate the different wall elimination effects of different explosion limit regimes, the impacts of surface reactions of six radicals (H, O, OH, HO₂, H₂O₂, and HCO) have been examined and the dominant radicals are found to be H and HO₂. The H radicals significantly influence the first explosion limit, while the HO₂ radicals impact the entire explosion limit.

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.

FeH is one of the most challenging diatomic molecules to study under electronic structure theory. Here, we have successfully studied 22 electronic states of FeH using ab initio multireference configuration interaction (MRCI), Davidson-corrected MRCI (MRCI+Q), and coupled cluster singles, doubles, and perturbative triples [CCSD(T)] levels of theory. We report their potential energy curves (PECs), excitation energies, dissociation energies, equilibrium electronic configurations, and a series of spectroscopic constants with the use of augmented triple-ζ, quadruple-ζ, and quintuple-ζ quality correlation consistent basis sets. The scalar relativistic effects and active space and core electron correlation contribution on the properties of FeH are also explored. The use of a large CASSCF active space that includes 4s, 4p, 3d, and 4d orbitals of Fe and the 1s of H is critical for producing accurate full PECs with proper dissociations and predicting the exact order of the electronic states. Our findings are in harmony with the experimental results available in the literature and will serve as reference values for future studies of FeH. Furthermore, with the use of PECs, the total internal partition function sum (TIPS) of FeH was calculated across a range of temperatures. Finally, we exploited the single-reference nature of the a⁶Δ of FeH and its ionized product FeH⁺ (X⁵Δ) to evaluate the associated density functional theory (DFT) errors on their dissociation energies and spectroscopic parameters.

Carbamic acid (H₂NCOOH) is a small organic molecule that is terrestrially unstable in condensed phases under ambient conditions but could survive in the low densities and temperatures of the interstellar medium. In this work, the reaction of formamide (H₂NCOH) and electronically excited oxygen atoms in the ¹D state, namely, O(¹D), has been investigated computationally to determine the feasibility of carbamic acid production. Geometries for carbamic acid and other potential reaction products have been calculated, as well as all pertinent transition states. In addition, harmonic and anharmonic frequency calculations were performed to determine quartic and sextic centrifugal distortion constants for all products. This work enables spectroscopic predictions that can guide the experimental search for carbamic acid. Presented here are the calculations, geometries, molecular constants, and spectral predictions for possible products of the reaction between formamide and O(¹D), as well as a discussion of which products are favored.