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A long-held belief is that shock energy induces initiation of an energetic material through an indirect energy up-pumping mechanism involving phonon scattering through doorway modes. In this paper, a 3-phonon theoretical analysis of energy up-pumping in RDX is presented that involves both direct and indirect pathways where the direct energy transfer dominates. The calculation considers individual phonon modes which are then analyzed in bands. Scattering is handled up to the third order term in the Hamiltonian based on Fermi's Golden Rule. On average, modes with frequencies up to 90 cm-1 scatter quickly and redistribute the energy to all the modes. This direct stimulation occurs rapidly, within 0.16 ps, and involves distortions to NN bonds. Modes from 90 to 1839 cm-1 further up-pump the energy to NN bond distortion modes through an indirect route within 5.6 ps. The highest frequency modes have the lowest contribution to energy transfer due to their lower participation in phonon-phonon scattering. The modes stimulated directly by the shock with frequencies up to 90 cm-1 are estimated to account for 52 to 89\% of the total energy transfer to various NN bond distorting modes., There is a significant error in this paper. Please refer to the corrected version that is now available in the corresponding journal article https://pubs.acs.org/doi/10.1021/acs.jpca.1c03225

We present the results of a theoretical study on dynamic Stark-induced coherent π-electron rotations in a chiral aromatic ring molecule. This is an extension of our previous papers, which have been published in Mineo , H. [ Phys. Chem. Chem. Phys. 2016 , 18 , 26786 - 26795 ] and Mineo , H. [ J. Phys. Chem. Lett. 2018 , 9 , 5521 - 5526 ]. In those papers, the time-dependent Schrodinger equation was solved under a restricted condition in which a degenerate excited state should be formed at the center of the two relevant excited states by dynamic Stark effects. The dynamic Stark-induced degenerate state (DSIDS) is essential to create unidirectional π-electron rotations. In the present theoretical treatment, the above restriction is relaxed and the DSIDS is set to be at any energy position between the two excited states. This indicates a wide applicability of the dynamic Stark effects to coherent control of photophysical properties in aromatic molecules, such as coherent ring currents and current-induced magnetic fluxes of low-symmetric aromatic molecules. Analytical expressions for the coherent π-electron angular momentum are derived within a three-electronic-state model by using the Laplace transform method. The validity of the developed theoretical procedure is demonstrated by carrying out simulations of the coherent angular momentum of l-phenylalanine. Effects of varying the DSIDS on the time-dependent coherent angular momentum and the populations in the three electronic states are examined, and the results are analyzed using approximate expressions for the time-dependent coherent angular momentum and the populations. Modulations in the time-dependent coherent angular momentum appear when the DSIDS is set at an energy position between the two excited states, while there are no beating modulations when the DSIDS is set at the center position. Such differences originate from whether interferences between the two dressed states take place or not.

The accurate evaluation of the Wigner phase space density for multidimensional system remains a challenging task. Path integral Monte Carlo methods offer a numerically exact approach for obtaining the Boltzmann density in coordinate space, but the Fourier-type integral required to construct the Wigner distribution generally leads to poor convergence. This paper describes a path integral method for constructing the Wigner density which substantially mitigates the Monte Carlo sign problem and thus is applicable to systems with many degrees of freedom. The starting point is the path integral representation of the coherent state density, which does not involve a Fourier integral and thus converges rapidly. We then use the relation between the coherent state and Wigner densities to construct the Wigner function, taking advantage of destructive phase cancellation to truncate the infinite series and thus confine the integrand, avoiding highly oscillatory regions. We also describe the use of information-guided noise reduction (IGNoR) to improve the Monte Carlo statistics in the most challenging regimes. The method is applied to strongly anharmonic one-dimensional models, a system-bath Hamiltonian, as well as the formamide molecule within an ab initio quartic potential, and the results are compared to those obtained by various approximate methods. These calculations suggest that the coherent state-based path integral method described in this paper offers an efficient, numerically exact approach for constructing the Wigner phase space density in systems of many degrees of freedom, and thus will be useful for quantizing the initial condition in classical trajectory-based simulations of dynamical properties.

For a nozzle jet beam, one fascinating fact is where a transition occurs from continuous to discontinuous beam during the expansion, which is typically known as the quitting surface. In our previous work, we applied a pickup method to investigate the fragmentation properties of water cluster during electron ionization, and we roughly estimated the possible quitting surface position (∼1 to 1.5 mm in front of the nozzle) to make sure the dopants were not accelerated by the beam expansion. Thus, the momentum conservation law can be applied to evaluate the possible fragmented water molecules. In this work, we applied a simple thermodynamic method to more accurately calculate the position of quitting surface of supersonic beam based on speed measurements. From our calculation in this paper, the quitting surface should be exactly located 1 mm in front of the nozzle, and this paper can further support our previous work.

An important but virtually ignored 1978 paper by Reeves and co-workers, which examined a dye-OAc hydrolysis and then agglomeration system, is reanalyzed in light of current state of knowledge of nucleation and growth/agglomeration phenomena. The Finke-Watzky two-step mechanism is used to account quantitatively for the kinetics data, in turn providing deconvolution of dye hydrolysis and nucleation of agglomerative growth, from the agglomerative growth step, including their separate rate constants. Significantly, the effects of microfiltration of the removable dust on the two steps and their rate constants are uncovered and quantitated for the first time, including the finding that the presence of dust accelerates both steps by ca. 10-fold or more. A postulated minimum mechanism able to account for all the observed results is provided. The results allow the excellently designed and executed, now nearly 40-years old, classic studies of Reeves and co-workers to be placed in its proper position in history, while at the same time providing six insights and conclusions detailed in the Discussion and Conclusions sections of the paper.

The mechanism of the O((3)P) + CH3CCH reaction was investigated using a combined experimental/theoretical approach. Experimentally the reaction dynamics was studied using crossed molecular beams (CMB) with mass-spectrometric detection and time-of-flight analysis at 9.2 kcal/mol collision energy. Theoretically master equation (ME) simulations were performed on a potential energy surface (PES) determined using high-level ab initio electronic structure calculations. In this paper (II) the theoretical results are described and compared with experiments, while in paper (I) are reported and discussed the results of the experimental study. The PES was investigated by determining structures and vibrational frequencies of wells and transition states at the CASPT2/aug-cc-pVTZ level using a minimal active space. Energies were then determined at the CASPT2 level increasing systematically the active space and at the CCSD(T) level extrapolating to the complete basis set limit. Two separate portions of the triplet PES were investigated, as O((3)P) can add either on the terminal or the central carbon of the unsaturated propyne bond. Minimum energy crossing points (MECPs) between the triplet and singlet PESs were searched at the CASPT2 level. The calculated spin-orbit coupling constants between the T1 and S0 electronic surfaces were ∼25 cm(-1) for both PESs. The portions of the singlet PES that can be accessed from the MECPs were investigated at the same level of theory. The system reactivity was predicted integrating stochastically the one-dimensional ME using Rice-Ramsperger-Kassel-Marcus theory to determine rate constants on the full T1/S0 PESs, accounting explicitly for intersystem crossing (ISC) using the Landau-Zener model. The computational results are compared both with the branching ratios (BRs) determined experimentally in the companion paper (I) and with those estimated in a recent kinetic study at 298 K. The ME results allow to interpret the main system reactivity: CH3CCO + H and CH3 + HCCO are the major channels active on the triplet PES and are formed from the wells accessed after O addition to the terminal and central C, respectively; (1)CH3CH + CO and C2H3 + HCO are the major channels active on the singlet PES and are formed from the methylketene and acrolein wells after ISC. However, also a large number of minor channels (∼15) are active, so that the system reactivity is quite complicated. The comparison between computational and experimental BRs is quite good for the kinetic study, while some discrepancy with the CMB estimations suggests that dynamic non-ergodic effects may influence the system reactivity. Channel specific rate constants are calculated in the 300-2250 K and 1-30 bar temperature and pressure ranges. It is found that as the temperature increases the H abstraction reaction, whose contribution is negligible in the experimental conditions, increases in relevance, and the extent of ISC decreases from ∼80% at 300 K to less than 2% at 2250 K.

In this paper, potential energy curves of Λ

In this paper, a multiscale physics-informed neural network (MPINN) approach is proposed based on the regular physics-informed neural network (PINN) for solving stiff chemical kinetic problems with governing equations of stiff ordinary differential equations (ODEs). In MPINNs, chemical species with different time scales are grouped and trained by multiple corresponding neural networks with the same structure. The adaptive weight based on a key performance indicator is assigned to each loss term when calculating the summation of loss residues. With this structure, MPINNs provide a framework to solve challenging stiff chemical kinetic problems without any stiffness-removal artifacts before training. In addition, by introducing a small number of ground truth data (GTD) points (less than 10% of the number required for residual loss calculation) and adding data loss terms into loss functions, MPINNs show superior ability to represent stiff ODE solutions at any desired time. The accuracy of MPINNs is tested with classical chemical kinetic problems, by comparing with the regular PINN and other state-of-the-art methods with special consideration for solving stiff chemical kinetic problems with PINNs. The validation results show that MPINNs can effectively avoid the influence of stiffness on neural network optimization. Compared with the traditional deep neural network only trained by GTD, MPINNs can use no data or a relatively small amount of data to achieve high-precision prediction of stiff chemical ODEs. The proposed approach is very promising for solving stiff chemical kinetics, opening up possibilities of MPINN application in different fields involving stiff chemical dynamics.

This paper reports correlated product distributions for dissociation of the van der Waals complexes NO-CH

Bioluminophore of bioluminescence (BL) comes from the decomposition of peroxide, which is an intermediate produced in the complicated chemical reactions of BL. The peroxide is a dioxetanone in most BL cases and an endoperoxide in fungal BL. The decomposition mechanisms of these two types of peroxides have been exclusively studied. However, the peroxide is a linear organic peroxide in bacterial BL, whose decomposition explanations are quite controversial, and seven mechanisms have been proposed. To thoroughly understand the mechanism of bioluminophore production in bacterial BL, this paper systematically discusses the seven proposed mechanisms via the present computational results and previous experimental and theoretical results. Our research results indicate that the bioluminophore in bacterial BL is produced through the charge-transfer initiated luminescence (CTIL) mechanism. The decomposition mechanism of linear organic peroxide was compared with the decomposition mechanisms of the other two types of peroxides, dioxetanone and endoperoxide. This study is also helpful in understanding the bioluminophore production in other BLs via the decomposition of an organic peroxide, such as dinoflagellate BL.

Polarization and inductive effects are the concepts that have been widely used in qualitative and even quantitative descriptions of experimentally observed properties in chemistry. The polarization effect has proven to be important in cases of biomolecular modeling though still the vast majority of molecular simulations use the classical non-polarizable force fields. In the last few decades, a lot of effort has been put into promoting the polarization effect and incorporating it into modern force fields and charge calculation methods. In contrast, the inductive effect has not attracted such attention and is effectively absent in both classic and modern force fields. Thus, a question is whether this difference corresponds to the difference in the physical significance of the effects and their explicit account, or is an artifact that should be corrected in the next generation of force fields. The significance of the electronic effects is studied in this paper through the prism of performance of specific models for atomic charge calculation that take into explicit account a nested set of effects: the formal charge, the nearest neighbors, the inductive effect, and finally the model, which takes into account all effects, which are possible to account for using atomic charges. The specific choice for the methods is the following: formal charges, MMFF94 bond charge increments, Dynamic Electronegativity Relaxation (DENR), and RESP. We propose a special scheme for the separate estimation of each particular effect contribution. By pairwise comparing the residual molecular electrostatic potential (MEP) errors of those charge models (aimed at best reproducing the quantum chemical reference MEP), we sequentially revealed how the account of each effect contributes to the better-quality MEP reproduction. The following relative importance of effects was estimated; thus, the natural hierarchy of the effects was established. First, the account of formal charges is of primordial importance. Second, the nearest neighbors account is the next in significance. Third, the explicit account of inductive effect in empirical charge calculation schemes was shown to significantly─both qualitatively and quantitatively─improve the quality of MEP reproduction. Fourth, the contribution of polarization is indirectly assessed. Surprisingly, it is of the order of magnitude of the inductive effect even for the molecular systems, for which it is anticipated to be more significant. Finally, the relative importance of anisotropic effects in neutral molecules was additionally reviewed.

The experimental field of ultracold ion-atom mixtures including an alkali-metal atom and an alkaline-earth-metal ion as well as of homonuclear alkali dimers has paved the way for creating and manipulating the ultracold molecules. The present paper is focused on a study of molecules such us francium dimer and a comparative spectroscopic investigation of the cationic systems Fr-(Ca

This paper investigates the electric properties of the photochromic dihydroazulene/vinylheptafulvene system as it is physisorbed onto silver and copper nanoparticles. Our focus is on how the polarizability and hyperpolarizability of the dihydroazulene, s

Functionalized metal nanoparticles (NPs) have been proposed as promising radiosensitizing agents for more efficient radiotherapy treatment using photons and ion beams. Radiosensitizing properties of NPs may depend on many different parameters (such as size, composition, and density) of the metal core, the organic coatings, and the molecular environment. A systematic exploration of each of these parameters on the atomistic level remains a formidable and costly experimental task, but it can be addressed by means of advanced computational modeling. This paper describes a detailed computational procedure for construction and atomistic-level characterization of radiosensitizing metal NPs in explicit molecular media. The procedure is general and is extensible to many different combinations of the core, coating, and environment. As an illustrative and experimentally relevant case study, we consider nanometer-sized gold NPs coated with thiol-poly(ethylene glycol)-amine molecules of different length and surface density and solvated in water at ambient conditions. The radial distribution of different atoms in the coatings as well as distribution and structural properties of water around the coated NPs are analyzed and linked to radiosensitizing properties of the NPs. It is revealed that the structure of the coating layer on the solvated NPs depends strongly on the surface density of ligands. At surface densities below ∼3 molecules/nm

In this paper, we introduced an order parameter, named the local structure similarity (LSS), to measure the resemblance of a cluster structure in a liquid with respect to a perfect crystal. The LSS is based on a dot product of two bond orientational order complex vectors, with one vector associated with a particle in a liquid and the other vector with a particle in a crystal. The calculation of the LSS should scan the entire space of the Euler angles determined by the two coordinate frames describing individually the liquid and the crystal. The effectiveness of the LSS was examined by solid-like clusters in a Lennard-Jones (LJ) system near its liquid-solid phase transition and at solid states below its melting point, where the thermodynamic states of the LJ system were obtained by simulation annealing. The LSS measure was utilized to scrutinize the fcc-like, hcp-like, and bcc-like clusters classified by criteria based on

Dicarboxylic acids are ubiquitous products of the photooxidation of volatile organic compounds which are believed to play a significant role in the formation of secondary organic aerosols in the atmosphere. In this paper, we report high-level quantum investigations of the clustering properties of sulfuric acid and benzenedicarboxylic acid molecules. Up to four molecules have been considered in the calculations, and the behavior of the three isomers of the organic diacid species have been compared. The most stable geometries have been characterized together with the corresponding thermodynamic data. From an atmospheric point of view, the results of the DFT calculations show that the organic diacid molecules may significantly enhance the nucleation of small atmospheric clusters, at least from an energetic point of view. In this respect, the phthalic acid isomer seems more efficient than the two other isomers of the benzenedicarboxylic acid, in particular because the internal distance between the two carboxyl groups in the organic diacids appears to play an important role in the stabilization of the H-bond network inside the corresponding heterocluster formed with sulfuric acid molecules.

This paper is the second part of a study on the effects of a substituted 5'-phenylenevinylene (PV) functionality on the emission properties of 2-(2'-hydroxyphenyl)benzoxazole (HBO)─a dye that is known for excited-state intramolecular proton transfer. The topical compounds are referred to as

π-conjugated aromatic diimides with chemical stability, heat resistance, and redox activity have attracted more attention due to their excellent fluorescence quantum yield in solution. The planar perylene diimide (PDI) derivatives generally have aggregation-induced emission quenching in the solid state, while the cyclic trimers based on pyromellitic diimides (PMDIs), naphthalene diimides (NDIs), and PDIs can increase the fluorescence quantum yield in the solid state and have large two-photon absorption cross section, which can be used as excellent nonlinear optical (NLO) materials. Therefore, this paper will study the effects of multiple assembly modes of the three monomers on the NLO responses of materials. It was found that the assembly modes of 2PMDI-1NDI and 2NDI-1PDI exhibit larger third-order NLO response (γ) values, which was due to the larger conjugate surface of PDI effectively reducing the energy gap between the HOMO and LUMO. Compared with other assembly methods, 2PMDI-1NDI and 2NDI-1PDI were conducive to causing redshifts (150 nm) in the absorption spectrum. Therefore, the larger conjugate surface of PDI and the assembly mode of the isosceles triangle were more favorable for intramolecular charge transfer, thus improving its NLO properties.

This paper presents the reaction mechanism, cross sections, and product energy partitioning for the O + CO

This paper contributes to the further understanding of bond resonance energy (BRE), circuit resonance energy (CRE), and ring currents (RC = I) as indices for the measure of local ring aromaticity and topological resonance energy (TRE) and magnetic resonance energy (MRE) as indices for the measure of global molecular aromaticity. Calculations of ring currents in the 3-ring polycyclic hydrocarbons of anthracene, biphenylene, phenalenyl, and p-terphenyl are demonstrated. This comparative study provides new molecular insights. A number of shortcut techniques are briefly illustrated. p-Terphenyl is a benzenoid total resonant sextet (TRS) and biphenylene is shown to be a nonbenzenoid TRS, i.e., both obey Clar's sextet principle. p-Terphenyl has only ring circuits, whereas anthracene, biphenylene, and phenalenyl have ring circuits and larger circuits engulfing the ring circuits. The perimeter circuits of anthracene, biphenylene, and phenalenyl engulf all other circuits, thus leading to the definition of MRE. By these several aromatic indices, the monocation, monoanion, and monoradical of phenalenyl are equally aromatic. The agreement in the prediction of local ring aromaticity between the three indices of m-BRE, t-BRE, and CRE is evaluated.

X-ray characterization techniques are invaluable for probing material characteristics and properties, and have been instrumental in discoveries across materials research. However, there is a current lack of understanding of how X-ray-induced effects manifest in small molecular crystals. This is of particular concern as new X-ray sources with ever-increasing brilliance are developed. In this paper, systematic studies of X-ray-matter interactions are reported on two industrially important catalysts, [Ir(COD)Cl]

In this paper, we have investigated the chemical adsorption behavior of O2 on five types of organic sulfur (thiol, sulfoxide, thioether, sulfone, and thiophene) in polycyclic aromatic hydrocarbon (PAH) sheets using density functional theory (DFT) calculations. Here, the adsorption energy of O2-organic sulfur exceeds that of O2-PAH. Sulfone tends to be more favorable for oxidation reactions than other organic sulfur compounds and PAH by energy gap and deformation charge density analyses. A large charge transfer occurs between O2 and organic sulfur compounds by charge analysis. A radical distribution function (RDF) analysis shows that O2/CO2/N2 is preferentially adsorbed on nitrogen/sulfur/oxygen-containing functional groups in coal. To inhibit the reaction of sulfur-containing coal with oxygen, the physical adsorption of pure gas (CO2/O2/N2) and binary mixed gases (CO2 + O2/N2 + O2/CO2 + N2) is conducted at different temperatures and geological depths using molecular dynamics (MD) and grand canonical Monte Carlo (GCMC) simulations. The adsorption capacities of five types of organic sulfur with respect to the pure gases decrease with increasing temperature and increase with increasing depth. For O2/CO2, CO2/N2, and O2/N2 binary gas systems, the order with respect to adsorption amount is CO2 > O2 > N2. The factor of adsorption capacities is also evaluated, and the results show that pore volume plays a key role in adsorption behavior.

Electron attachment to DNA by low energy electrons can lead to DNA damage, so a fundamental understanding of how electrons interact with the components of nucleic acids in solution is an open challenge. In solution, low energy electrons can generate presolvated electrons, epre-, which are efficiently scavanged by pyrimidine nucleobases to form transient negative ions, able to relax to either stable valence bound anions or undergo dissociative electron detachment or transfer to other parts of DNA/RNA leading to strand breakages. In order to understand the initial electron attachment dynamics, this paper presents a joint molecular dynamics and high-level electronic structure study into the behavior of the electronic states of the solvated uracil anion. Both the valence π* and nonvalence epre- states of the solvated uracil system are studied, and the effect of the solvent environment and the geometric structure of the uracil core are uncoupled to gain insight into the physical origin of the stabilization of the solvated uracil anion. Solvent reorganization is found to play a dominant role followed by relaxation of the uracil core.

Photodissociation of vibrationally and electronically excited sulfur dimer molecules (S2) has been studied in a combined experimental and computational quantum chemistry study in order to characterize bound-continuum transitions. Ab initio quantum chemistry calculations are carried out to predict the potential energy curves, spin-orbit coupling, transition moments, and bound-continuum spectra of S2 for comparison with the experimental data. The experiment uses velocity map imaging to measure S-atom production following S2 photoexcitation in the ultraviolet region (320-205 nm). A pulsed electric discharge in H2S produces ground-state S2 X3ςg -(v = 0-15) as well as electronically excited singlet sulfur and b1ςg +(v = 0, 1), and evidence is presented for the production and photodissociation of S2 a1Δg. In a previous paper, we reported threshold photodissociation of S2X3ςg -(v = 0) in the 282-266 nm region. In the present study, S(3PJ) fine structure branching and angular distributions for photodissociation of S2 (X3ςg -(v = 0), a1Δg and b1ςg +) via the B″3IIu, B3ςu - and 11IIu excited states are reported. In addition, photodissociation of the X3ςg -(v = 0) state of S2 to the second dissociation limit producing S(3P2) + S(1D) is characterized. The present results on S2 photodynamics are compared to those of the well-studied electronically isovalent O2 molecule.

Quantum mechanics/molecular mechanics (QM/MM) calculations are widely used embedding techniques to computationally investigate enzyme reactions. In most QM/MM computations, the quantum mechanical region is treated through density functional theory (DFT), which offers the best compromise between chemical accuracy and computational cost. Nevertheless, to obtain more accurate results, one should resort to wave function-based methods, which however lead to a much larger computational cost already for relatively small QM subsystems. To overcome this drawback, we propose the coupling of our QM/ELMO (quantum mechanics/extremely localized molecular orbital) approach with molecular mechanics, thus introducing the three-layer QM/ELMO/MM technique. The QM/ELMO strategy is an embedding method in which the chemically relevant part of the system is treated at the quantum mechanical level, while the rest is described through frozen ELMOs. Since the QM/ELMO method reproduces results of fully QM computations within chemical accuracy and with a much lower computational effort, it can be considered a suitable strategy to extend the range of applicability and accuracy of the QM/MM scheme. In this paper, other than briefly presenting the theoretical bases of the QM/ELMO/MM technique, we will also discuss its validation on the well-tested deprotonation of acetyl coenzyme A by aspartate in citrate synthase.

The measurement of optical rotation (OR) is a foundational technique for the detection and characterization of chiral molecules, but it is poorly understood how the observed property relates to the structure of the molecule. Over the years, several schemes have been developed to decompose the OR into more chemically intuitive contributions. In this paper, we introduce two alternative formulations of our previously developed

This paper reports a photophysical investigation of a series of phenylene ethynylene oligomers (OPE) that are end-substituted with a 1,8-naphthalene imide (NI) acceptor. The NI acceptor is attached to the terminus of the OPEs via an ethynylene (-C≡C-) unit that is linked at the 4-position of the NI unit. A series of three oligomers is investigated, OPE1-NI, OPE3-NI, and OPE5-NI, which contain 1, 3, and 5 phenylene ethynylene repeat units, respectively. The properties of the OPEn-NI series are compared to a corresponding set of unsubstituted OPEs, OPE3 and OPE5, which contain 3 and 5 phenylene ethynylene repeats, respectively. The photophysics of all the compounds are interrogated using a variety of techniques including steady-state absorption, steady-state fluorescence, two-photon absorption, time-resolved fluorescence, and transient absorption spectroscopy on femtosecond-to-microsecond time scales. The effect of solvent polarity on the properties of the oligomers is examined. The results show that the NI-substituted oligomers feature a lowest charge transfer (CT) excited state, where the OPE segment acts as the donor and the NI moiety is the acceptor (OPEn•+-NI•-). The absorption spectra in one-photon and two-photon exhibit a clear manifold of absorption features that can be attributed to direct CT absorption. In moderately polar solvents, the emission is dominated by a broad, solvatochromic band that is due to radiative decay from the CT excited state. Ultrafast transient absorption provides evidence for initial population of a locally excited state (LE) which in moderately polar solvents rapidly (∼1 ps) evolves into the CT excited state. The structure, spectroscopy, and dynamics of the CT state are qualitatively similar for OPE3-NI and OPE5-NI, suggesting that delocalization in the OPE segment does not have much effect on the structure or energetics of the CT excited state.

Though density functional theory is widely accepted as one of the most successful developments in theoretical chemistry in the past few decades, the knowledge of how to apply this new electronic structure theory, to help us better understand chemical processes and transformations, is still an unaccomplished task. The information-theoretic approach is emerging as a viable option for that purpose in the recent literature, providing new insights about steric effect, cooperativity, electrophilicity, nucleophilicity, stereoselectivity, homochirality, etc. In this work, based on the result from a recent paper by one of us [ J. Chem. Phys, 2019, 151, 141103], we present two quantifications of the relative Fisher information and discuss their physiochemical properties and possible applications. To that end, their analytical properties have been elucidated. They have also been applied to six categories of systems to illustrate their applicability. A better descriptor to quantify the single bond rotation barrier has been obtained. The relative Fisher information can also simultaneously determine electrophilicity and nucleophilicity, and effectively describe helical structures with different homochiral and heterochiral propensities. As integral parts of the information-theoretic approach, these newly introduced quantities will provide us with more analytical tools toward the long-term goal of crafting a chemical reactivity theory in the density-based language.

Ephemeral intermediates often hold the key to a more detailed understanding of chemical reaction pathways. Online methods to unambiguously identify the structure of such molecular entities, in particular in the presence of multiple isomers, are scarce. This paper presents a methodology that allows real-time monitoring of isomeric solution-phase reaction intermediates of continuous-flow reactions by coupling a microfluidic chip-reactor to a cryogenic ion trap triple mass spectrometer. The technique combines the excellent reaction control associated with microfluidic chips with the unique specificity and sensitivity of infrared photodissociation (IRPD) spectroscopy, which allows for an unambiguous structural assignment of gaseous ions based on their IR fingerprint. It represents a valuable extension to the instrumentation for online-analysis of reactive intermediates and proves particularly valuable whenever the sensitivity of NMR is not sufficient. After a brief description of the experimental approach, illustrative examples are provided to highlight the application of the chip-IRPD setup for mechanistic studies, particularly for stereoselective processes. The article concludes with an outlook on future challenges and perspectives.

Molecules containing sulfur-nitrogen bonds, like sulfonamides, have long been of interest because of their many uses and interesting chemical properties. Understanding the factors that cause sulfonamide reactivity is important, yet there continues to be controversy regarding the relevance of S-N π bonding in describing these species. In this paper, we use sulfur K-edge X-ray absorption spectroscopy (XAS) in conjunction with density functional theory (DFT) to investigate the role of S

Photobases are compounds that become more basic when promoted to an excited electronic state. Previous experimental and computational studies have demonstrated that several quinoline and quinoline-derived compounds are strong photobases (pKa* > 14). Moreover, the strength of photobasicity was shown to depend strongly on the identity and position of the substituent group(s), with the strongest photobases having multiple electron-donating substituents on a fused benzene ring as opposed to the ring containing the photobasic nitrogen atom. These electron-donating substituents build up electron density on one side of the molecule that shifts onto the nitrogen-containing ring in the electronic transition. This shift in electron density produces an increase in negative charge on the ring nitrogen atom responsible for the photobasicity. In this paper, we expand on our previous investigation to study the effect of an additional ring nitrogen atom on photobasicity in aromatic heterocycles. In particular, we consider how the thermodynamic driving force for excited-state protonation can be tuned by changing the relative placement of the ring nitrogen atoms and varying the position and number of electron-donating substituents. In the set of 112 molecules screened, we identified 42 strong photobases with generally comparable pKa* but lower vertical excitation energies than the quinoline derivatives with only a single ring nitrogen atom. We additionally explored photobasicity in substituted azaindole and carboline derivatives, identifying 76 strongly photobasic compounds with pKa* as large as 22.6 out of the 155 compounds that we considered. Overall, this work provides new insights into the design principles necessary to develop next-generation photocatalysts that employ photobasicity.

This paper presents a comprehensive potential energy surface (PES) for hydrogen atom addition to and abstraction from 2-methyl-1-butene, 2-methyl-2-butene, and 3-methyl-1-butene and the subsequent ß-scission and H atom transfer reactions. Thermochemical parameters for species on the Ċ

This paper investigates vibrational excitation effects on valence electron momentum distributions of dimethyl ether. A symmetric noncoplanar (e, 2e) experiment has been performed for the molecule at a high temperature (980 K) as well as at room temperature (300 K). For comparison, theoretical calculations with vibrational effects being involved have also been carried out. Changes of the momentum profiles with the rise of temperature are observed for the 2b1 and 6a1 orbitals, indicating that distortion of these molecular orbitals is appreciably enhanced upon excitation of the methyl torsional vibrations. The present study provides a way for exploring the influence of vibrational excitation on electronic wavefunctions of molecules.

We report a theoretical investigation and elucidation of the X-ray absorption spectra of neutral benzene and of the benzene cation. The generation of the cation by multiphoton ultraviolet (UV) ionization and the measurement of the carbon K-edge spectra of both species using a table-top high-harmonic generation source are described in the companion experimental paper [Epshtein, M.; et al. J. Phys. Chem. Ahttp://dx.doi.org/10.1021/acs.jpca.0c08736]. We show that the 1sC → π transition serves as a sensitive signature of the transient cation formation, as it occurs outside of the spectral window of the parent neutral species. Moreover, the presence of the unpaired (spectator) electron in the π-subshell of the cation and the high symmetry of the system result in significant differences relative to neutral benzene in the spectral features associated with the 1sC → π* transitions. High-level calculations using equation-of-motion coupled-cluster theory provide the interpretation of the experimental spectra and insight into the electronic structure of benzene and its cation. The prominent split structure of the 1sC → π* band of the cation is attributed to the interplay between the coupling of the core → π* excitation with the unpaired electron in the π-subshell and the Jahn–Teller distortion. The calculations attribute most of the splitting (∼1–1.2 eV) to the spin coupling, which is visible already at the Franck–Condon structure, and we estimate the additional splitting due to structural relaxation to be around ∼0.1–0.2 eV. These results suggest that X-ray absorption with increased resolution might be able to disentangle electronic and structural aspects of the Jahn–Teller effect in the benzene cation.

Traditionally, chemistry problems are solved by means of a deductive approach. The question to be addressed is typically related to the value of a property that is either measured experimentally, computed using quantum-chemistry software, or (more recently) predicted using a machine-learned model. In this paper, we demonstrate that an inductive approach can be adopted using End-to-End (E2E) machine learning. This approach is illustrated for tackling the following chemistry problems: (i) determine the fully coordinated (FC) and undercoordinated (UC) atoms in a molecule with one missing atom, (ii) identify the type of atom that is missing in such an incomplete molecule, and (iii) predict the direction of a reaction between two molecules according to an existing dataset. The E2E approach leads to accuracies higher than 99%, 98%, and 93% for these three problems, respectively. Finally, in order to achieve such accuracies, a descriptor for the molecules, called bag of clusters, is introduced and compared with a series previously proposed descriptors, highlighting a series of advantages.

An ab initio chemical kinetics study of the reactions of methyl butanoate (MB) with hydroperoxyl radical (HO2) is presented in this paper. Particular interest is placed on determining the influences of torsional anharmonicity and addition reaction on the rate constants of hydrogen abstraction reactions. Stationary points on the potential energy surface of MB + HO2 are calculated at the level of QCISD(T)/CBS//B3LYP/6-311++G(d,p). The transition state theory (TST) is used to calculate the high-pressure limit rate constants of the hydrogen abstraction reactions over a board range of temperature (500-2000 K). Anharmonicity of low-frequency torsional modes is considered in the rate calculations by using the one-dimensional hindered rotor approximation and the internal-coordinate multistructural approximation; the latter is used as a higher-level theoretical method to examine the applicability of the former in dealing with strongly coupled torsional modes. The calculated rate constants are compared with the available data from the literature and observed discrepancies are analyzed in detail. An energetically lowest-lying addition reaction with subsequent isomerization and decomposition reactions are identified on the potential energy surface. The multiple-well Master equation analysis shows that these reactions have a secondary influence on the rate constants in the temperature range of interest.

This paper presents a study of a CH

Dielectric microstructures coupled with a conventional optical microscope have been proven to be a successful way to achieve super-resolution imaging. However, a limitation of such super-resolution imaging is the microstructure fabrication ability, which generally provides natural structures (such as spherical, hemispherical, superhemispherical microlenses, and so on). Meanwhile, the influences of microstructures with complex shapes on the super-resolved imaging still remain unknown. In this paper, direct laser writing (DLW) lithography is used to produce a series of complex microstructures, which are capable of achieving super-resolution imaging in the optical far-field region. Cylinder, truncated cone, hemisphere, and protruding hemisphere microstructures are successfully fabricated by this 3D printing technology, allowing us to resolve features as small as 100 nm under classical microscopy. Moreover, different microstructures lead to different photonic nanojet (PNJ) illuminations and collection efficiencies, resulting in a critical role in super-resolved imaging. The microstructures with spherical surfaces can easily collect the light scattered by the object and convert the high-spatial-frequency evanescent waves into propagating waves.

In this paper, we report a quasi-classical trajectory study of the internal energy state specificity of dissociative O

Of all plastics, the most abundantly produced is polyethylene, most of which is destined for landfills, shipping ports, and natural environments. The limited degradability and recyclability of this synthetic polymer motivates the development of chemical recycling methods. One possible approach consists of selective depolymerization to propylene with tandem olefin metathesis and double bond isomerization catalysts. In this paper, we transform thousands of coupled rate equations, pseudo-steady-state approximations, and local density approximations into one simple and analytically solvable Fokker-Planck type equation. The Fokker-Planck equation gives concise expressions for the rate of propylene production and polymer molecular weight evolution as functions of catalyst concentrations, rate constants, and ethylene concentrations.

This paper reports an energy-partition mechanism in dissociative excitation of alkali cyanide molecules, MCN (M = Rb, K, Na), to produce CN(B

Purely organic phosphors with persistent room-temperature phosphorescence (RTP) demonstrate promising potential applications in optoelectronic area, bioimaging, and chemical sensing. However, it is still a formidable challenge to further design new organic phosphors due to the unclear mechanism to produce ultralong phosphorescence lifetimes. This paper investigates the correlation between the ultralong phosphorescence lifetime and structure of a series of 4-carbonylphenylboronic acid derivatives in the crystal state. Experimental and calculation results reveal that the electron-donating effect of substituents makes the phosphorescence lifetime longer by not only weakening the vibration relaxation of the excited triplet state but also increasing the energy of T

Photothermal (PT) microscopy enables the efficient detection of absorbing nano-objects with high sensitivity and stability. The PT signal in the current PT microscopy usually comes from the interaction of the probe laser beam with the heating laser beam-induced thermal lens, and the contribution of the scattering field from the imaged nano-object is usually not taken into account. Here, in this paper, we systematically studied the influence of the scattering field from the imaged nanoparticles on the obtained PT signal by using Ag nanowires (NWs) on a glass substrate surrounded by glycerol as an example. Under the excitation of a heating laser beam at 532 nm wavelength, the rise of local temperature around the Ag NW results in the intensity variation of the interferometric scattering probe light at 730 nm wavelength which includes the scattering light from the Ag NW and the reflection light from the glass-glycerol interface. We found that the PT signal on the NW are positive and negative for the probe beam polarized parallel and perpendicular to the NW axis, respectively. Numerical simulations confirm that the heat-induced intensity variation of the pure scattering light from the NW and the thermal lens-induced intensity increase of the reflection light both contribute to the obtained PT signal. Our work provides the basic guidance for the analysis of PT signal from nano-objects with large scattering cross sections.

The multiplet theory of free ions combined with crystal field theory is used to study core electron excitation of perovskites. This combined method is helpful to further identify transition peaks and comprehend the transition mechanism. In this paper, the core electron excitation of Ti K edge, L