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• A five-dimensional potential surface for N2 -N 2 O involving the Q 3 asymmetric-stretch normal-mode coordinate was built. • Each averaged potential exhibits two equivalent skew T-shaped global minima and two equivalent shallow local minima. • The determined band origin shift in the infrared spectra in the N 2 O ν 3 regionagrees well with the experimental value. We propose a new potential energy surface for the N 2 –N 2 O complex, which encompasses the Q 3 normal mode for the ν 3 antisymmetric stretching coordinate of N 2 O. The interaction potential energies were obtained at the explicitly correlated coupled cluster with single, double, and perturbative triple excitations [CCSD(T)-F12a] level with aug-cc-pVTZ basis set plus mid-bond functions. Four-dimensional vibrationally averaged potentials with N 2 O in the ground and ν 3 excited states were generated through integration over the Q 3 coordinate. Both potentials exhibit two equivalent skew T -shaped global minima. The rovibrational energies were calculated by employing the radial discrete variable representation/angular finite basis representation approach. The determined fundamental band origin shift of the infrared spectra in the N 2 O ν 3 region, transition frequencies and rotational constants are all consistent with the experimental values. [ABSTRACT FROM AUTHOR]

[Display omitted] • Experimental and theoretical investigation of ortho- , meta- , and para- chlorophenylboronic acid derivatives. • The FT-IR, FT-Raman, and UV–Vis spectroscopic properties are studied. • Conformational analysis using by DFT/B3LYP and HF methods. • The dipole moments, vibrational frequencies, polarizability, and hyperpolarizability are calculated. • Assignment of fundamental vibrational modes of stable conformers. In this study, the FT-IR, FT-Raman, and UV–Vis spectroscopic properties of three monosubstituted phenylboronic acid derivatives: ortho -chlorophenylboronic acid (o -ClPhBA), meta -chlorophenylboronic acid (m -ClPhBA) and para -chlorophenylboronic acid (p -ClPhBA) molecules are investigated both experimentally and theoretically using Density Functional Theory (B3LYP) and Hartree Fock (HF). In order to find the stable possible conformations of the compounds, the conformational analysis was carried out by running potential energy surface (PES) scan by means of rotation of two structural parameters, the dihedral angles indicated as φ2 (C6–B–O1–H1A) and φ3 (C6–B–O2–H2A), varying from −180° to 180° with an increment of 10° using B3LYP/6-31G level of theory. Also, to determinate the most stable conformer for all the molecules, potential energy curve (PEC) the stable possible conformations on PES scan were investigated as a function of φ1 (C1-C6–B–O1) dihedral angle from 0° up to 180° with an increment of 10° using B3LYP/6–311++G(d,p) and HF/6–311++G(d,p) level of theory. For all the studied compounds, two conformational structures (conformer anti-anti, syn-syn) that did not have imaginary frequency values outside the equilibrium state (conformer anti-syn) were detected theoretically at the both methods. Due to their conformational flexibility, the relative stabilities of the anti-syn , anti-anti , and syn-syn conformers of o -ClPhBA, m -ClPhBA, and p -ClPhBA are 0.0, 4.66, and 6.76 kcal/mol, respectively, at the B3LYP/6–311++G(d,p) level of theory. For the HF/6–311++G(d,p) level of theory, the relative stabilities are 0.00, 4.54, and 6.11 kcal/mol for o -ClPhBA; 0.00, 3.98, and 1.51 kcal/mol for m -ClPhBA; and 0.00, 4.10, and 1.44 kcal/mol for p -ClPhBA, respectively. Some of the determined stable conformations of these molecules are different in symmetry groups. It was observed that the increase in the symmetry was effective in the of molecular properties, especially for vibrational frequencies. The structural parameter, dipole moments (μ), vibrational frequencies, polarizability (α), hyperpolarizability (β), the highest occupied molecular orbital (HOMO), and the lowest unoccupied molecular orbital (LUMO) of the stable conformers were calculated by using Ab initio HF/6–311++G(d,p) and DFT/B3LYP/6–311++G(d,p) level of theory. The assignments of fundamental vibrational modes of the studied molecule were performed based on total energy distribution (TED) analysis. [ABSTRACT FROM AUTHOR]

[Display omitted] • Dual hydrogen bond strengthening resulting from photoexcitation facilitates ESIPT tendency for D3HF derivatives. • Charge redistribution and related variation of atomic charge promote ESIPT reaction for D3HF-O, D3HF-S and D3HF-Se fluorophores. • Variation of atomic electronegativity could play a regulatory effect on the single ESIPT behavior of D3HF and its derivatives. Inspired by the distinguished photochemical characteristics of new organic molecule containing the chalcogenide substitution that could be potentially applied across various disciplines, in this work, the effects of atomic electronegativity of chalcogen (O, S and Se) on hydrogen bond interactions and proton transfer (PT) reaction. We present the characteristic 2,8-diphenyl-3,7-dihydroxy-4H,6H-pyrano[3,2-g]-chromene-4,6-dione (D3HF), which is based on 3-hydroxyflavone (3HF) and contains intramolecular double hydrogen bonds that is the main objective of this study to explore in detail the influence of the change of atomic electronegativity on the dual hydrogen bond interaction and the excited state proton transfer (ESPT) behavior by photoexcitation. By comparing the structural changes and infrared (IR) vibrational spectra of the D3HF derivatives (D3HF-O, D3HF-S and D3HF-Se) fluorophores in S 0 and S 1 states, combined with the preliminary detection of hydrogen bond interaction by core-valence bifurcation (CVB) index, we can conclude that the hydrogen bond is strengthened in S 1 state, which is favorable for the occurrence of ESPT reactions. The charge recombination behavior of hydrogen bond induced by photoexcitation also further illustrates this point. Via constructing potential energy surfaces (PESs) based on restrictive optimization, we finally clarify the excited state single PT mechanism for D3HF derivatives. Specially, we confirm change of atomic electronegativity has a regulatory effect on the ESIPT behavior of D3HF and its derivatives, that is, the lower the atomic electronegativity is more conducive to the ESIPT reaction. [ABSTRACT FROM AUTHOR]

The potential energy surface of formic acid anhydride has been investigated at highly accurate quantum chemical methods. The rotation of CHO group in global minimum conformer of formic acid anhydride can lead two different local minimum conformers. Both local minimum conformers are around three kcal/mol higher in energy than the global minimum conformer. One conformer is planar and another has two rotamers which rapidly interconvert to each others via planar transition state. In some earlier studies, this planar transition state has incorrectly assigned to be a local minimum structure. We calculated anharmonic vibrational frequencies for the global and local minimum energy conformers and compared the theoretical wavenumbers with experimental gas phase and argon matrix measurements. Our results suggest that some of the experimentally detected peaks are overtone and combination bands. In previous studies with harmonic calculations, those peaks have assigned to be fundamental bands with zero intensities. We confirmed that the higher energy conformer produced in argon matrix by ultra violet induced rotamerization of global minimum conformer belongs to the planar conformer. • Calculated accurate potential energy surface of formic acid anhydride. • Saddle point energies are computed at the coupled cluster level. • Anharmonic vibrational calculations show new band assignments in experimental spectrum. [ABSTRACT FROM AUTHOR]

[Display omitted] • A global MgH 2 + ground-state potential energy surface is represented and the Mg+(2S) + H 2 /HD reaction mechanism is discussed. A globally accurate ground-state MgH 2 + potential energy surface (PES) is constructed by neural network method based on 12,056 high-level ab initio points. On the PES, the dynamics calculations of the Mg+(2S) + H 2 /HD (v 0 = 0, j 0 = 0) reaction are performed using the time-dependent wave packet method. The branching ratio (MgD+/MgH+) in the Mg+ + HD reaction is much larger than one in most studied collision energies. The dynamics results imply that the title reaction follows the complex-forming mechanism near the threshold, and the direct abstraction process gradually plays the dominant role as the collision energy increases. [ABSTRACT FROM AUTHOR]

MgAlSi alloy materials have the main properties of light weight and high strength, good electrical and thermal conductivity and corrosion resistance, and have various applications in the industrial field, making an important contribution to the realization of lightweight and high performance needs. In order to be able to predict the material properties of MgAlSi alloys with a high degree of accuracy, this paper develops for the first time an interatomic potential function for MgAlSi alloys based on a neural network machine learning approach. The effectiveness of the developed machine learning potentials is verified by analyzing the problems encountered during the training process and the errors of the finally obtained potential functions, and comparing some of the radial distribution functions, coordination numbers, and predictions of properties such as the equation of state, lattice constants, shear modulus and bulk modulus with those of AIMD. It is found that the performance error of the deep potential model is basically kept in the same order of magnitude as that of DFT calculations, the computational speed can be up to nearly a thousand times that of DFT, and the computational cost is linearly related to the atomic number, which is well suited for large-scale molecular dynamics simulations, and it will provide a promising solution for accurate large-scale molecular dynamics simulations. [Display omitted] • Interatomic potential functions for MgAlSi alloys are developed based on MLP. • Analyzing problems in training and errors in potential functions. • Calculation of mechanical properties from the developed potential function. • Calculated results and efficiencies were compared with and AIMD. [ABSTRACT FROM AUTHOR]

In this study, the kinetics of hydrogen abstraction reaction H + HCF 3 → H 2 + CF 3 are studied using both tunneling-corrected transition state and quasi-classical trajectory methods on a newly developed global potential energy surface (PES). The PES is constructed by fitting 31 968 ab initio points at the level of UCCSD(T)-F12a/aug-cc-pVTZ using the permutation invariant polynomial-neural network method. The thermal rate coefficients determined for both the forward and reverse reactions exhibit satisfactory agreement with the experimental observations, affirming the accuracy of the potential energy surface. In addition, an investigation into the kinetic isotope effects on the reverse reaction is carried out by substituting H 2 with D 2. These findings collectively serve as explicit evidence that quantum tunnelling plays a significant role, even under elevated temperature conditions. [ABSTRACT FROM AUTHOR]

A new global potential energy surface (PES) for the ground state of CaH 2 system was constructed by using neural network method. This paper provides a comprehensive discussion on the topographical characteristics of the PES and the spectral properties of stationary points. Furthermore, a time-dependent wave packet method was used to perform the dynamics studies on the Ca(4 s 2 1 S) + H 2 reaction based on the newly constructed PES. Some meaningful dynamics results are reported, including reaction probabilities, integral cross sections and differential cross sections. In addition, the reaction mechanism of the Ca(4 s 2 1 S) + H 2 reaction was discussed in detail. [ABSTRACT FROM AUTHOR]

In order to develop reliable combustion models of biodiesel, the low-temperature oxidation kinetics of methyl pentanoate (MP), the smallest methyl ester with the negative temperature coefficient (NTC), is theoretically investigated. We use the DLPNO-CCSD(T)/CBS(T-Q)//M06-2X/cc-pVTZ and CASPT2/CBS(T-Q)//CASSCF(7e,5o)/cc-pVTZ methods to explore the potential energy surfaces (PESs) of the decomposition of different MP peroxy radicals, including dissociation, isomerization, and concerted HO 2 elimination. Comparisons among the PESs of MP and other methyl esters reveal that the ester functional group inherently affects the low-temperature oxidation kinetics of methyl esters, and the energies of the species along the PESs are closely related to the active C site and the alkyl chain length. Based on the determined PESs, the pressure- and temperature-dependent rate constants for the low-temperature oxidation of MP are computed at 298 − 1200 K and 0.01 − 100 atm. The kinetic calculations suggest that the dissociation rate constants of different methyl ester peroxy radicals are similar at the same active C site, and the channels that lead to tri-molecular products are significant during the low-temperature oxidation of large methyl esters. The literature combustion model of MP is revised with our calculations. For the first time, the NTC behavior of MP is theoretically predicted by the revised model, and an excellent agreement between the predictions and the measurements reflects the reliability of the present low-temperature oxidation subset of MP. Novelty and Significance statement Methyl pentanoate (MP) is the smallest methyl ester with the negative temperature coefficient (NTC), but the low-temperature oxidation kinetics in the available combustion model of MP is still insufficient to interpret its NTC behavior. To develop a reliable combustion model for MP, the potential energy surfaces (PESs) of the decompositions of different MP peroxy radicals are investigated. Results show that the ester functional group inherently affects the low-temperature oxidation kinetics of methyl esters, and the energies of the species along the PESs are closely related to the active C site and the alkyl chain length. With our calculated rate constants, the literature combustion model is revised. For the first time, the NTC behavior of MP is theoretically predicted by the revised model, and an excellent agreement between the predictions and the measurements reflects the reliability of the present low-temperature oxidation subset of MP. [ABSTRACT FROM AUTHOR]

[Display omitted] • Dual hydrogen bond strengthening resulting from photoexcitation facilitates ESIPT tendency for FT derivatives. • Charge redistribution and related variation of atomic charge promote ESIPT reaction for FT-O, FT-S, and FT-Se fluorophores. • Variation of atomic electronegativity could play a regulatory effect on the excited state intramolecular single PT behavior for FT derivatives. Inspired by fascinating photochemical and photophysical characteristics of novel organic molecules with chalcogenide substitution, this study focuses on exploring the effects of atomic electronegativity of chalcogens (O, S, and Se) on hydrogen bond interactions and proton transfer reaction mechanisms for 3-hydroxy-2-(5-(5-(5-(3-hydroxy-4-oxo-4H-chromen-2-yl)thiophen-2-yl)thiophen-2-yl)thiophen-2-yl)-4H-chromen-4-one (FT). By comparing structural changes and infrared (IR) spectra, combined with preliminary detection of hydrogen bond interaction by core-valence bifurcation (CVB) index, we conclude S 1 -state hydrogen bond is strengthened, which is favorable for occurrence of ESIPT reaction. Charge recombination and constructed potential energy surfaces (PESs) reveal atomic electronegativity has a regulatory effect on ESIPT behavior for FT derivatives. [ABSTRACT FROM AUTHOR]

[Display omitted] • Additional electron causes H 2 CS- to change into a slightly curved umbrella structure. • The changes in the structure of H 2 CS- are manifested through the out of plane bending vibration and the inverse barrier appearing in the potential energy surface. • The photoelectron spectrum of H 2 CS− X ∼ 2 B 1 → H 2 CS X ∼ 1 A 1 at different temperatures were calculated. The equilibrium structures, multidimensional potential energy surfaces, and anharmonic vibrational frequencies of thioformaldehyde (H 2 CS) and its 2B 1 radical anion were obtained at the (U)CCSD(T)-F12a/cc-pVTZ-F12 level; and the photoelectron spectrum of H 2 CS− X ∼ 2 B 1 → H 2 CS X ∼ 1 A 1 was simulated by calculating the Franck-Condon factors (FCFs). The additional electrons cause a significant change in the bond length of the C = S bond of H 2 CS, which affects the potential energy surface and the C = S bond stretching mode, while the interaction between electrons turns the originally planar structure of H 2 CS into a slightly out-of-plane umbrella structure, resulting in an unusual change in the vibrational frequency of the out-of-plane bending mode. Finally, a time-independent eigenstate-free Raman wave function approach (RWF) was used to calculate the photoelectron spectrum of H 2 CS and to point out the changes in the band under the influence of different temperatures. These data provides a theoretical basis for interstellar observations and experimental studies. [ABSTRACT FROM AUTHOR]

A novel water-soluble stilbene-type molecular photoswitch (CP) has been synthesized by attaching an N -methylpyridinium unit to 7-diethylamino-4-methylcoumarin (coumarin 1) via an ethylene bridge. The photoisomerization cycle of CP and the spectroscopic properties of the two isomers were studied in acetonitrile and in water. In both solvents, the illumination of trans -CP with green light leads to a photostationary state (PSS) with 90% cis isomer and irradiating then this PSS mixture with near UV light, the trans isomer is almost fully recovered. In water, the quantum yield for the trans - cis photoisomerization is 0.042, for the cis - trans photoisomerization it is 0.23. In acetonitrile, the photoisomerization quantum yields are even higher, the respective values are 0.12 and 0.56. The trans isomer of CP is fluorescent with red emission and it has a large Stokes shift, whereas the cis isomer is non-fluorescent. The two isomers are thermally stable at room temperature. The efficient photoisomerization of CP in both direction, the thermal stability of both isomeric forms and the distinct fluorescence of the trans isomer suggest that some water-soluble coumarin-based photoswitches may be promising candidates for applications in fluorescence imaging of biological samples. [Display omitted] • A new water-soluble stilbene-type molecular photoswitch was synthesized. • The photoswitch is 7-diethylamino-coumarin connected with a vinylpyridinium unit. • The trans isomer of the photoswitch is fluorescent, the cis isomer is dark. • The photoisomerization reactions proceed with high quantum yields in both directions. • The photochemical behavior of the photoswitch was interpreted on the basis of PES calculations. [ABSTRACT FROM AUTHOR]

[Display omitted] • Metal-free amination of perfluoro aromatic compounds occurs in the presence of light. • Charge transfer from solvent to arene rings occurs in an excited state. • The existence of two minima on the excited states correspond to different nature of charge transfers. • There is a marked reduction in reaction-barrier in going from ground to excited state. • Reductive cleavage of carbon-halogen bond generates halide ions. Mechanistic insights into the synthetically-valued metal-free sustainable N , N -dimethylamination of perfluoroarenes have been investigated. Density functional theory (DFT) and time-dependent DFT (TD-DFT) have been applied to provide details regarding photo-assisted cleavage of N , N -dimethylformamide (DMF) for the valued N , N -dimethylamination reaction. The radical reaction mediated by the electron transfer process causes DMF cleavage, which is responsible for the amination reaction. It was found that the energy barrier for the ground state reaction is thermally prohibitive. On the other hand, visible-light irradiation activates the electron-donor properties of DMF and acceptor properties of perfluoronaphthalene (PFN), so that the energy barrier for electron transfer reduces to ∼ 14 kcal/mol. The redistribution of the electronic charge between the DMF and PFN generates an imbalance of charge on the overall molecule. These events prompt the relocation of extraneous charges to some antibonding molecular orbitals so that one of the C-F bonds in PFN gets weakened and is easily broken. The reductive cleavage of the C-F bond enables the radical ions to react quickly to afford the amination products, which eventually deactivate to the ground state. [ABSTRACT FROM AUTHOR]

Although C 5 H 4 isomers are detected in flames, they are not thoroughly incorporated into detailed chemical kinetics models (DCKMs). Here we use RRKM/ME modelling to simulate C 5 H 4 + H reactions on a C 5 H 5 potential energy surface. Kinetic studies indicate that C 3 H 3 + C 2 H 2 is the main fate but fall-off from the initial adduct isomer back to C 5 H 4 + H cannot be ignored at relevant combustion temperatures of 900 to 2000 K. Calculated rate coefficient expressions were incorporated into a DCKM for a toluene flame, along with updates to other relevant reactions from the recent literature, particularly the open-chain 1-vinylpropargyl radical, l -C 5 H 5. Obtained species mole fractions were found to be in good agreement with published experimental data for a low-pressure toluene flame, with a significant improvement in predicted concentration of the cyclopentadienyl radical. The presented DCKM will allow for further reactions of C 5 H x species such as 1-vinylpropargyl to be included in combustion simulations. [ABSTRACT FROM AUTHOR]

[Display omitted] Based on a combination of quantum chemistry and atom–atom potentials methods, we developed a technique for modeling the structure and estimating the complexation energy of a binary organic complex in gas and crystal phases. The efficiency of this technique was illustrated by an example of the benzotrifuroxan–benzene molecular complex. For both phases, the same molecular binary structure (π-stacking) was obtained with a parallel arrangement of the planes of BTF and benzene molecules and complexation energies of −11.9 and −11.7 kcal mol−1 for a gas phase and a crystal cluster, respectively. [ABSTRACT FROM AUTHOR]

A new three-dimensional potential energy surface of the electronic ground state of the chloronium ion, H 2 Cl + , based on the explicitly correlated coupled cluster method with a triple zeta basis set adapted to this method has been expanded in an analytical representation. This potential energy surface is later incorporated into our home-made Fortran code to compute variationally the vibrational levels, zero-point ground average structural parameters and the rotational constants of the chloronium ion and several isotopologues. Our results show a good agreement with experimental data and that our results will help to detect H 2 Cl + isotopologues in the interstellar medium. [Display omitted] • Potential energy surface of the chloronium cation, H 2 Cl + • Anharmonic vibrational levels and transitions of H 2 Cl + and isotopologues. • Zero-point average structure and rotational constants of H 2 Cl + and isotopologues. [ABSTRACT FROM AUTHOR]

• AFBD experiences a cooperative ESIDPT process in acetonitrile solvent. • The cooperative ESIDPT is converted into stepwise ESIDPT by introducing –Br or –OCH 3. • The substitution of electronic groups OCH 3 →H→Br can accelerate the ESIDPT process. In this paper, the effect of different electronic group substituents on the excited state intramolecular double proton transfer (ESIDPT) in AFBD is comprehensively researched by using quantum chemistry methods. Two electronic groups with comparable capabilities, including the electron-withdrawing group (-Br) and the electron-donating group (–OCH 3), are chose to accomplish this study. The obtained geometric parameters, reduced density gradient and infrared spectra calculations have demonstrated that AFBD and its two derivatives experience the ESIDPT process. Subsequently, the conclusion of the potential energy surface and Bonn-Oppenheimer molecular dynamics further unveil that AFBD undergoes a cooperative ESIDPT process at ∼15 fs. Nevertheless, it should be noted that the introduction of -Br and –OCH 3 transforms the proton transfer path. That is: "the cooperative ESIDPT is converted into the stepwise ESIDPT". Besides, we also confirm that the substitution of the electronic groups OCH 3 →H→Br can accelerate the ESIDPT process. Our work not only regulates the path of ESIDPT process, but also provides a time scale for this process, which is conducive to developing new intelligent fluorophores based on ESIDPT behavior. [Display omitted] [ABSTRACT FROM AUTHOR]

• BPDC undergoes the concerted ESDPT process in CHY and H 2 O solvents. • The concerted ESDPT process of BPDC is induced at 62 fs (CHY) and 19 fs (H 2 O). • The IEHBs formed by BPDC and H 2 O accelerates the ESDPT process. This study has conducted a systematic investigation into the excited state double proton transfer (ESDPT) process of 2,2′-bipyridine-3,3′-diol-5,5′-dicarboxylate acid ethyl ester (BPDC) in cyclohexane (CYH) and water (H 2 O) by density functional theory (DFT) and time-dependent density functional theory (TDDFT) methods. The calculated geometrical parameters, reduced density gradient and infrared vibration spectra confirm that BPDC undergoes the ESDPT process in both CYH and H 2 O. In comparison to the CYH solvent, the intramolecular hydrogen bonds (IAHBs) are strengthened in the S 0 state by the formation of centrosymmetric intermolecular hydrogen bonds (IEHBs) between H 2 O and the OH group of BPDC molecules. Furthermore, the constructed potential energy surfaces show that BPDC molecules undergo a concerted ESDPT process without potential barriers in both solvents. Time evolution analysis confirms that the ESDPT process of BPDC molecules in H 2 O solvent (19 fs) is faster than that in CYH solvent (62 fs). The results indicate that the formation of IEHBs causes zero disruption to the original I AHBs, but it can effectively promote the ESDPT process of BPDC molecules. Overall, this work serves as important theoretical guidance for the development of high-performance fluorescence materials. [Display omitted] [ABSTRACT FROM AUTHOR]

In this research, the authors investigated a new material called honeycomb borene (HB), which exhibits an attraction-induced superlubricity (AISL) phenomenon and shows potential for experimental exploration of the load-induced superlubricity phenomenon. AISL is dominated by Coulomb interactions between the tip (AFM) and HB surfaces, which are caused by load-tuned electron redistribution. By comparing the sliding behaviors of various tips on HB surface supported by a metal substrate, it is found that the sliding of Ag tip on HB/Ti (0001) surface is the best choice for AISL experimental verification. Subsequently, the feasibility of AISL experiment was demonstrated in detail by analyzing the binding of substrate to HB plate and the adsorption between HB surface and tip. The results of this study provide new insights for experimental exploration and may help push the progress of load-induced superlubricity from theory to experiment. [Display omitted] • The friction force of a silver tip slides on a honeycomb borophene monolayer is found to vary nonlinearly with the tip height. • The friction force turns out to be almost null when the tip height approaches a value corresponding to a critical normal attraction force. • The experimental feasibility of the attraction-induced superlubricity (AISL) is argued by analyzing the different relevant factors. A nanoscale friction test using an atomic force microscope (AFM) is modelled as a diatomic tip in sliding contact with a 2D monolayer supported by a metal substrate. This test is simulated by ab initio DFT calculations. The simulation results show that, when a silver tip slides on a honeycomb borophene (HB) monolayer supported by a titanium substrate, the friction force varies nonlinearly with the prescribed height of the tip or, equivalently, the corresponding normal force exerted by the tip on the HB monolayer. In particular, the friction force turns out to be almost null when the height of the tip sufficiently approaches a critical height of the prescribed height, which corresponds to a critical normal attraction force. This nanoscale friction-free sliding phenomenon is thus qualified as attraction-induced superlubricity (AISL). Further, the origin of AISL is discussed and analyzed in terms of electron redistributions. Finally, the feasibility of AISL detection is argued by analyzing the potential energy surface (PES), the adsorption strength of the tip on HB surface and the binding strength of HB to its substrate. [ABSTRACT FROM AUTHOR]

The self-assembly of proteins is encoded in the underlying potential energy surface (PES), from which we can predict structure, dynamics, and thermodynamic properties. However, the corresponding analysis becomes increasingly challenging with larger protein sizes, due to the computational time required, which grows significantly with the number of atoms. Coarse-grained models offer an attractive approach to reduce the computational cost. In this Feature Article, we describe our implementation of the UNited RESidue (UNRES) coarse-grained potential in the Cambridge energy landscapes software. We have applied this framework to explore the energy landscapes of four proteins that exhibit native states involving different secondary structures. Here we have tested the ability of the UNRES potential to represent the global energy landscape of proteins containing up to 100 amino acid residues. The resulting potential energy landscapes exhibit good agreement with experiment, with low-lying minima close to the PDB geometries and to results obtained using the all-atom AMBER force field. The new program interfaces will allow us to investigate larger biomolecules in future work, using the UNRES potential in combination with all the methodology available in the computational energy landscapes framework. [Display omitted] • UNRES Model: A coarse-grained model with two interaction sites. • OPTIM Program: Searching energy landscape and calculating stationary points. • UNOPTIM Program: UNRES model integrated into OPTIM. • Benchmarks with All-Atom: UNOPTIM significantly faster. • Exploring Energy Landscape: UNOPTIM offers useful accuracy. [ABSTRACT FROM AUTHOR]

[Display omitted] • Water molecules can be used as hydrogen bond bridges to produces a synergistic excited intermolecular double-proton transfer process, which effectively reduces the ESIPT barrier. • The drastically increased water fraction in the solvent inhibits the ESIPT reaction. • The phenomenon of fluorescence quenching can be ascribed to the increased polarity of solvent and stimulative ICT process. • Our work provides a theoretical basis for the synthesis of new Schiff base fluorescent chromophores for the water detection in organic solvents. The 8-hydroxyquinoline-2-carboxaldehyde thiosemicarbazone (HQCT) is sensitive to water molecules in dimethyl sulfoxide according to the experimental phenomenon description, with a sensory performance that is dependent on the water-based hydrogen bond bridge as mediator. Here the excited state intramolecular (ESAPT) and intermolecular (ESEPT) proton transfer mechanism involved by water solvent and the optical properties associated with them are clarified in details. Along the minimum energy pathways in the scanned potential energy surfaces (PESs), we find that the ESEPT reaction induced by water molecule is a synergistic double-proton transfer process. And the results indicate that trace water molecules can promote the reaction effectively. In addition, we also investigate the photophysical properties involved with the excited state proton transfer (ESPT) reaction with the increase of water fraction in the solvent. The results show that the fluorescent oscillator strength (f) and radiative rates (k r) decrease with the increase of water fraction, which are consistent with the experimental phenomenon. We attribute the phenomenon of fluorescence quenching to the increasing transition dipole moment (μ) which accelerates the intramolecular charge transfer (ICT) process. Our work not only explain the water-detection mechanism in the organic solvent before water-sensitive reactions essentially, but also provide a theoretical basis for the synthesis of new Schiff base fluorescent chromophores for the water detection in organic solvents. [ABSTRACT FROM AUTHOR]

• CO 2 reacts with methyl groups to both promote and inhibit combustion. • CO 2 is weakly oxidizing and can participate in chemical reactions. • CO 2 also reacts with formaldehyde, ethylene and vinyl. The study aims to examine the impact of CO 2 concentration gradient on the ignition and combustion of a diesel surrogate fuel composed of 70% C 7 H 16 and 30% C 7 H 8. The investigation focuses on the weak oxidation of CO 2 through its reaction with methyl groups (CH, CH 2 , and CH 3 radicals). Firstly, the molecular bond-breaking recombination process between CO 2 and methyl groups is calculated using Born-Oppenheimer molecular dynamics with the UB3LYP/6–311++g (d, p) level of theory. Subsequently, the electronic distribution and competition of the molecule surface are analyzed through various wave function analyses to identify the reactive sites. Secondly, the precise potential energy surface and reaction rate are calculated based on the acquired reaction process information. This calculation employs the B2PLYP/def2-TZVP level of theory and transition state theory. Finally, extensive molecular dynamics simulations of CO 2 and methyl groups are conducted using reaction force fields. These simulations provide insights into the temperature-energy variation within the system and the resulting chemical reaction network. The optimized combustion mechanism for the binary fuel is derived, focusing exclusively on the influences of CO 2 and O 2 while excluding those of N 2 and other extraneous gases. The results demonstrate exothermic reactions of CO 2 with CH and CH 2 radicals at 850 K, yielding ΔG values of −238.91 kJ/mol and −209.96 kJ/mol, respectively. Conversely, CO 2 reacts with CH 3 radicals in heat-absorbing reactions at 850 K, resulting in a ΔG of 491.73 kJ/mol. Additionally, the chemical impact of CO 2 exhibits both promotional and inhibitory effects on combustion. The CO 2 molecule exhibits weak oxidation properties due to the presence of active sites on its surface characterized by minimal values of electrostatic potential (-50.17 kJ/mol) and average local ionization energy (61.92 kJ/mol) at the O-atomic end. The molecular dynamics process involving the methyl groups and CO 2 system exhibits a heat absorption phenomenon. This behavior can be attributed to the participation of CO 2 not only in the reactions with methyl groups but also with formaldehyde and ethylene, among others. [ABSTRACT FROM AUTHOR]

[Display omitted] • The ab initio potential energies of O 3 were computed with the extended CAS(24, 15) reference. • The SO coupling between 9 multiplet electronic states approaching D e was included. • An excellent agreement was achieved between the empirical and theoretical values of D e. • The long-range (R O 2 - O ≥5 a 0) ab initio PES was developed in the scattering coordinates. In this work an excellent agreement was achieved between the empirical (9230.08 ± 4.85 cm−1) and theoretical (9230.70 cm−1) values of the first dissociation limit (D e) of O 3. Ab initio multireference calculations were performed for the first time using the extended complete active space [CAS(24, 15)] reference in the icMRCI(Q) method combined with the extrapolation to the complete basis set limit [CBS(56Z)] and with the inclusion of the spin–orbit coupling between 9 multiplet electronic states approaching D e. Finally, the full-dimensional potential energy surface was developed in the scattering coordinates for the long-range region toward D e at this level of theory. [ABSTRACT FROM AUTHOR]

Which potential energy curve is correct? [Display omitted] • The most unexpected findings is that potential energy curves of HXeF⋅⋅⋅M 3 N 3 H 6 (M = B, Ga) with respect to the H 2 -H 1 -F-Xe dihedral angle depend on the density functional theories and the second order perturbation theory. • Thus, how to produce correctly these potential energy curves become a serious challenge for theoretical models. Theoretical studies on the weak interactions in HXeF⋅⋅⋅M 3 N 3 H 5 Y (M = B, Al and Ga; Y = H, F, Cl, Br, CF 3 , NH 2 and CH 3) have been carried out with B3LYP-D3(BJ)/aug-cc-pVTZ (aug-cc-pVTZ-PP for Xe). Electron-withdrawing groups make HXeF⋅⋅⋅M 3 N 3 H 5 Y more stable than electron-donating groups. AIM analysis indicates N-H⋅⋅⋅F interaction plays a dominant role in the stabilities of the studied complexes. It is found that potential energy curves of HXeF⋅⋅⋅M 3 N 3 H 6 (M = B, Ga) with respect to the H 2 -H 1 -F-Xe dihedral angle depend on the computational methods. Thus, how to produce correctly these potential energy curves becomes a serious challenge for the accuracy of theoretical models. [ABSTRACT FROM AUTHOR]

The C 3 H 5 O and C 3 H 5 O 2 potential energy surfaces accessed by the oxidation reactions of allyl radical with atomic and molecular oxygen have been mapped out at the CCSD(T)-F12b/cc-pVTZ-F12// ω B97XD/6-311G(d,p) level of electronic structure theory to unravel the reaction mechanism. Temperature- and pressure-dependent reaction rate constants have been evaluated using variable reaction coordinate transition state and RRKM-Master Equation theoretical kinetics methods. The C 3 H 5 + O reaction is found to be fast in the 300-2500 K temperature interval, with the total rate constant of 1.8-1.0 × 10−10 cm3 molecules s−1 independent of pressure in the considered 30 Torr – 100 atm range. Acrolein + H formed by a simple O addition/H elimination mechanism via the CH 2 CHCH 2 O association complex are predicted to be the major reaction products with the branching ratio decreasing from 61% at 300 K to 44% at 2500 K. Other substantial bimolecular products include C 2 H 3 + formaldehyde (32%-26%) formed through the C-C bond β-scission in CH 2 CHCH 2 O and two minor products C 2 H 4 + formyl radical HCO and allene + OH, where the latter, formed via direct H abstraction by O from the central carbon atom of allyl, becomes significant only at high temperatures above ∼1500 K. The C 3 H 5 + O 2 reaction studied in the 200-2500 K temperature range shows a peculiar kinetic behavior characteristic for a bimolecular reaction with a low entrance barrier, shallow association well, and high ensuing isomerization and decomposition barriers to bimolecular products. This behavior is described in terms of three distinct temperature regimes: the low-temperature one with slightly negative dependence of the rate constant, the intermediate one where the rate constant sharply drops, and the high-temperature regime with an Arrhenius-like rate constant. The rate constant is relatively high (10−13-10−12 cm3 molecule−1 s−1) in the low-temperature regime when the reaction produces the peroxy association complex CH 2 CHCH 2 OO, but slow at higher temperatures when it leads to bimolecular products. Under combustion relevant conditions, the C 3 H 5 + O 2 rate constant is by 5 to 3 orders of magnitude lower than that for C 3 H 5 + O, but since O 2 concentrations in flames could be as much as 3 orders of magnitude larger than O concentrations, C 3 H 5 + O 2 cannot be ruled out as a significant allyl radical sink. Above 1500 K, the C 3 H 5 + O 2 reaction can form vinoxy radical + formaldehyde (40%-15%) via the five- or four-membered ring closure and opening mechanism starting from the initial peroxy intermediate, acrolein + OH (41%-49%) via the H shift from the attacked carbon to the terminal oxygen followed by the immediate O-O bond cleavage, and allene + OH (18-25%) via the H migration from the central CH group to the terminal O atom accompanied or followed by the C-O bond rupture. Modified Arrhenius expressions fitting the computed rate constants for both reactions have been generated and proposed for kinetic models. [ABSTRACT FROM AUTHOR]

Ab initio calculations of the C 13 H 10 and C 13 H 9 potential energy surfaces related to the reaction of 1-acenaphthyl and methyl radicals and secondary isomerization of C 13 H 9 primary radical products have been performed at the chemically accurate G3(MP2,CC)//B3LYP/6-311G** level of theory to unravel the mechanism of conversion of acenaphthalene to phenalene or phenalenyl radical + H. The computed energetics and molecular parameters were utilized in Rice-Ramsperger-Kassel-Marcus Master Equation (RRKM-ME) calculations of reaction rate constants and relative product yields. The 1-acenaphthyl + CH 3 reaction is predicted to proceed by a fast radical-radical recombination mechanism and to predominantly produce collisionally stabilized 1-methylacenaphthalene B1 or a C 13 H 9 benzylic radical A1 + H with exothermicities of 106.8 and 25.2 kcal/mol, respectively. The A1 + H channel is preferable at higher temperatures, whereas the stabilization of 1-methylacenaphthalene is favored at higher pressures. The radical A1 can nearly irreversibly interconvert to phenalenyl radical AP via a 22.7 kcal/mol exothermic isomerization process involving formal insertion of the CH 2 group into a C C bond of the five-member ring leading to the expansion of this ring to a six-member ring. The rate constants for the H addition reaction to phenalenyl radical to form phenalene and the reverse H loss from phenalene were also computed and the strength of the weakest C H bond in the CH 2 group of phenalene is evaluated as 62.2 kcal/mol. The analysis of the reaction kinetics allowed us to deduce a mechanism for the conversion of 1-acenaphthyl radical to phenalene or phenalenyl radical + H via methylation involving the formation of A1 via a well-skipping channel or stabilization and dissociation of (or H abstraction from) B1 followed by isomerization of A1 to phenalenyl AP, which can add an H atom producing phenalene. Rate constants for the significant elementary reactions are fitted to modified Arrhenius expressions and are proposed for kinetic modeling of the expansion of a five-member ring on a zigzag edge of PAH to a six-member ring by methylation. [ABSTRACT FROM AUTHOR]

Although addition reactions of β -hydroxypropyl radicals with O 2 are important steps in the reaction pathways of propylene oxidation at low temperature, there is a lack of available accurate rate constants for these reactions in the literature. To obtain complete reaction channels and relatively accurate rate constants over a wide range of temperatures and pressures, a systematic method, which combines the high level ab initio calculation, the conventional transition state theory (TST), the variational transition state theory (VTST) and Rice-Ramsberger-Kassel-Marcus/Master-Equation theory (RRKM/ME), was used to investigate these reactions. The CCSD(T)/cc-pVTZ method was applied to calculate potential energy surfaces. High-pressure limit rate constants of barrierless reactions and those reactions with tight transition states were obtained using the VTST and the TST, respectively. RRKM/ME theory was used to compute rate constants in the fall-off range for pressure-dependent reactions. Take CC•COH as an example, the peroxy adduct of CC•COH with O 2 can further react to form more stable products, and subsequent reactions include H-shift reactions, HO 2 elimination reactions, OH elimination reactions and Waddington reaction. In these reactions, Waddington reaction is one of the most competitive advantage paths, as it has the lowest barrier. This conclusion is similar to that of those reactions about O 2 with products from OH addition to ethylene or isobutene. Rate constants of relevant reactions were fitted to the form of a modified Arrhenius expression, and were implemented into the existing mechanism to simulate concentration profiles of main species of propylene oxidation in a jet-stirred reactor. The results show that predicted results of the revised mechanism are closer to the experimental data than those of the original mechanism. Our calculated rate constants over a wide range of temperatures and pressures for these reactions are transferable and can be applied to a wider range of oxidation conditions. [ABSTRACT FROM AUTHOR]

Seven-membered N, O-ligands containing ketone and pyrrole have been designed and synthesized via a facile method using organocatalyst, piperidinium acetate or L-proline. Their photophysical properties including absorption and emission spectra have been investigated in eight kinds of different polar solvents. DFT and TD-DFT calculations have also been carried out to further demonstrate the geometric structures and illuminate their extraordinary photochemical properties. The calculations show that ESIPT process is prohibited in both compounds NOAB-1, 2 which is confirmed by experiment and calculation due to its stable ketone structure. Image 1 • Two seven-membered N, O-ligands (NOABs) have been synthesized by a facile method. • Photophysical properties are discussed by experiment and calculation. • ESIPT process of NOABs is prohibited which is confirmed by this work. [ABSTRACT FROM AUTHOR]

The atomic ions with hydrogen reactions play important role in biological chemistry, atmospheric and combustion chemistry. In this work, a full three-dimensional global many-body expansion potential energy surface (PES) for the ground state of H 2 S−(2A′) is reported for the first time, since there is almost no investigations can accurately and completely describe the PES. It is obtained using many-body expansion theory and an extensive set of accurate ab initio energies extrapolated to the complete basis set limit, for improving the accuracy of the potential energy surface. The topographical features of the new three-dimensional global potential energy surface are examined in detail, and found to be in good agreement with theoretical and experimental results. To better test the reaction, such a surface was applied to quasi classical trajectory calculations for S−(2P) + H 2 (1Σ g +) → SH−(1Σ) + H(2S) reaction. The integral cross sections, differential cross sections and the rate coefficients have been computed. Results indicate that such a work can be recommended for corresponding atmospheric dynamics studies and as building blocks for constructing the many body expansion potential energy surface of larger S−/H containing systems. Unlabelled Image • A full three-dimensional global potential energy surface for the ground state of H 2 S−(2A') is reported for the first time. • The topographical features of the new three-dimensional global potential energy surface are examined in detail. • The results found to be in good agreement with theoretical and experimental results. • Such a surface was applied to quasi classical trajectory calculations for the reaction S−(2P)+H 2 (1Ʃ g +). [ABSTRACT FROM AUTHOR]

• Point defect transformations can accelerate potential energy surface explorations. • Implemented according to three regimes: interstitial, neutral, and vacancy rich. • Application on fullerene clusters demonstrates new explorations pathways. • Energy super-basin history list enables further enhanced sampling during operation. The free and potential energy surfaces (F/PES) of atomistic systems contain important information regarding structural stability that is crucial in the development of new materials and devices. An effective method for navigating the energy surface can help to realize new synthesis pathways, fabrication techniques, and aid in the prediction of complex atomic structures. In most physical systems, an accurate exploration of the most stable atomic configurations in the FES can be computationally prohibitive using traditional, temperature dependent Monte-Carlo and dynamics based techniques due to the large spatial rearrangements and long time scales involved. In this work, we demonstrate the role of point defect (PD) mediated processes in navigating the PES by implementing PD transformations in a conventional PES exploration technique in order to enable shortcuts in finding the global energy minimum. Using the standard minima-hopping method as a means of sampling the PES, we discuss the details of a point defect mediated Minima-Hopping (PDMH) approach. We study the necessity of incorporating classification and biasing techniques during the search, such as a funnel characterization procedure with an accompanying super-basin history list. An example of our method is demonstrated on fullerene clusters starting from known, nearby low energy configurations. The results show that our method can enable pathways toward the global minimum energy configuration where an optimized MH calculation could not. The implications of such a method are discussed along with future areas of development. [ABSTRACT FROM AUTHOR]

Acetophenone (C 8 H 8 O, AP) is a common indoor air component but with no information on its atmospheric oxidation. The atmospheric oxidation mechanism of AP in gas phase, initiated by its reaction with the OH radical, is investigated here using quantum chemistry and chemical kinetics calculations. The reaction starts mainly by OH additions to the aromatic ring, and the predicted rate coefficient suggests a lifetime of ∼8 days in the atmosphere. The additions form adducts AP-i-OH (Ri) (i = 1, 2, 3, 4, the position on the aromatic ring). The adducts Ri would react with O 2 or undergo unimolecular decompositions. The adduct R1 reacts with O 2 rather slowly with an effective rate coefficients of <10−20 cm3 molecule−1 s−1, and it would alternatively decompose to phenol and acetyl radical. The dominate fate of R2, R3, and R4 in their reaction with O 2 proceeds via direct hydrogen-atom abstraction, forming hydroxyacetophenones, and only R3 would have a fraction of bicyclic radical formation as in oxidation of alkyl benzenes. The main products from oxidation of AP include phenol and three isomers of hydroxyacetophenones, suggesting that oxidation of AP by OH would reduce its unpleasant effect to human beings. [Display omitted] • Atmospheric lifetime of acetophenone is ∼8 days due to its reaction with OH. • Oxidation of acetophenone forms mainly the hydroxyacetophenones. • Oxidation of acetophenone reduces its health impact. [ABSTRACT FROM AUTHOR]

Abstract In order to understand the fine-tuned photo-physical behaviors of the N(X)–H⋯N systems, the excited state intramolecular proton transfer (ESIPT) switching in the N-substituted X 1 - 5 - NHIPA molecules (NHIPA = 2-(imidazo[1,2- a ]pyridin-2-yl)aniline and X = H, COCH 3 , CH 3 C 6 H 4 SO 2 , C 6 F 5 SO 2 , and COCF 3) were investigated in detail in gas phase and three solvent media at TD-PBE0/6-311++G(d,p) and TD-M06-2X/6-311++G(d,p) levels of theory. ESIPT reactions at S 1 state were approximately without energy barrier, exergonic processes and were quantitatively demonstrated to be mainly sensitive to substituents and solvent media. The X - NHIPA (X = CH 3 C 6 H 4 SO 2 , C 6 F 5 SO 2 and CF 3 CO) compounds were predicted to undergo fast, irreversible proton transfer at S 1 state and, in turn, exhibit tautomer emission with anomalous large Stokes shift in the gas phase. In the toluene solvent, except for C 6 F 5 SO 2 - NHIPA that showed exclusively a tautomer emission with a long wavelength, all other X - NHIPA molecules were predicted to involve in the reversible ESIPT and hence exhibit a dual normal and tautomer emissions behavior, in good agreement with the experimental observations. In polar solvents, it is expected that all compounds show dual normal and tautomer emissions. The nearly equal intensities of the normal and tautomer emissions can lead to the generation of the white lights with the potential in lighting applications. Graphical abstract Unlabelled Image Highlights • Photophysical properties of substituted X-NH⋯N molecules were evaluated. • Effect of the substituent on the ESIPT of X-NH⋯N type molecules was explored. • The normal and keto fluorescence emissions were predicted. • The potential energy surfaces were computed. • Effect of solvent on ESIPT reaction was investigated. [ABSTRACT FROM AUTHOR]

Abstract The cross second virial coefficient and three dilute gas transport properties (shear viscosity, thermal conductivity, and binary diffusion coefficient) of mixtures of water (H 2 O) and carbon dioxide (CO 2) were calculated with high accuracy for temperatures up to 2000 K using statistical thermodynamics and the kinetic theory of molecular gases, respectively. The required intermolecular potential energy surface (PES) for the H 2 O–CO 2 interaction is presented in this work, while the like-species interactions were modeled using PESs from the literature. All three PESs are based on high-level quantum-chemical ab initio computations. The predicted values for the cross second virial coefficient are in satisfying agreement with the best experimental data. In the case of the transport properties, the calculated values should be more accurate than the few available data sets. [ABSTRACT FROM AUTHOR]

Abstract A novel fluorescence molecule (2‑hydroxy‑4‑methoxyphenyl)(phenyl)‑methanone azine (HMPM) has been explored theoretically in this present work. Based on density functional theory (DFT) and time-dependent density functional theory (TDDFT) methods, we investigate the excited state hydrogen bonding behaviors and excite state intramolecular proton transfer (ESIPT) process for HMPM molecule. Via simulating the reduced density gradient (RDG) versus sign(λ 2)ρ, we firstly verify the double intramolecular hydrogen bonds (O1 H2⋯N3 and O4 H5⋯N6) for HMPM system. Comparing with the changes about these two hydrogen bonds (i.e., bond distances, bond angles and infrared (IR) vibrational spectra), we find that they should be enhanced in the first excited state upon the photo-excitation. The shortened hydrogen bonding distance of H2⋯N3 and H5⋯N6 provide the possibility for ESIPT reaction. Given the photo-excitation process, we confirm the charge redistribution around the hydrogen bonding moieties plays an important role as a driving force for the ESIPT process. Further, via constructing S 0 -state and S 1 -state potential energy surfaces (PESs), we confirm the excited state double proton transfer (ESDPT) is excludable since the high optimized energy and high potential energy barrier. While the low potential barrier for excited state single proton transfer path results in the ultrafast ESIPT reaction, which explains why the initial HMPM fluorescence peak cannot be detected in previous experimental phenomenon. This work not only clarifies the excited state dynamical behavior for HMPM system, but also explains previous experimental phenomenon and attributions about steady state spectra. We hope this work can facilitate novel applications based on the novel HMPM system in future. Graphical Abstract Unlabelled Image Highlights • Hydrogen bond of HMPM should be strengthened in the first excited state. • Charge transfer facilitates the ESIPT process for HMPM molecule. • Only the excited state single proton transfer process occurs for HMPM molecule. [ABSTRACT FROM AUTHOR]

Abstract Oxidation mechanism of an embedded five-member ring on a surface of a carbonaceous particle with atomic oxygen has been studied employing G3(MP2,CC)//B3LYP/6-311G* potential energy surface calculations for C 15 H 9 + O reactions. Temperature- and pressure-dependent reaction rate constants have been evaluated using the RRKM – Master Equation approach. The mechanism involves barrierless oxygen atom addition to a carbon atom on a free edge of a five-member ring followed by migration of the H atom from the attacked C atom to an ortho position followed by the five-member ring opening and elimination of the CO group, with the five-member ring being fully destroyed. When the embedded ring has three common sides with surrounding six-member rings and one free-edge carbon atom, the only product is the 4-phenanthrenyl radical. When the embedded ring has two common sides with the six-member rings and two free-edge C atoms, two different decarbonylation products possessing a phenalene core can be formed depending on the direction of the 1,2-H shift. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • The most stable isomer of 2-(tetrazol-5-yl)benzoic acid (TC) isolated in N 2 matrix. • Cis-trans photoisomerization of TC induced by tunable UV laser radiation. • Tetrazole ring cleavage and formation of carbodiimide derivative upon irradiation. Abstract A combined FTIR matrix isolation and theoretical B3LYP/6-311++G(2d,2p) study of 2-(tetrazol-5-yl)benzoic acid isolated in solid nitrogen was performed. Out of fifteen stable isomers of this molecule located on the singlet potential energy surface the most stable one, comprising the intramolecular N H⋯O hydrogen bond, was detected experimentally in nitrogen matrices after deposition. Upon irradiation with λ = 305 nm a new conformer of the precursor was generated and upon λ = 280 nm radiation a reverse photorotamerization reaction was induced. Simultaneously with the photoisomerizations, a cleavage of the tetrazole ring with dinitrogen elimination was observed proceeding with a very small rate and leading to formation of a carbodiimide derivative. [ABSTRACT FROM AUTHOR]

Abstract The higher level ab initio methods are performed to reduce an accuracy of three-dimensional adiabatic potential energies. And the accurate numerically fitted method, 3D-spline method, is used to get an accuracy adiabatic potential energy surfaces for the three lowest states of CCO molecule. Starting from reactants, the title reaction through the first two lowest states have no reaction barrier should be very fast. The title reaction pathways should be different depending on the angles that the oxygen atom O(3P) attacked the C 2 ( a 3 Π u ) molecule. If the angles less than 60 ° , the reaction pathway should be O(3P) + C 2 ( 3 Π u ) → CCO( C ∞ ) → CO( X 1 Σ) + C(1D); On the other hand, if the angles great than 65°the transition state should be take into account, the reaction pathway is O(3P) + C 2 ( 3 Π u ) → CCO( C 2 v ) → TS → CCO( C ∞ ) → CO( X 1 Σ) + C(1D). [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • A potential energy surface for the lowest 2A′ state of LiHO+ is constructed. • The ab initio energy points are extrapolated to the complete basis set limit. • The O + LiH+ reaction are investigated using the quasiclassical trajectory method. • The reaction mechanism ruling the O + LiH+ reaction changes with collision energy. Abstract A potential energy surface (PES) for the lowest 2A′ state of LiHO+ is constructed using ab initio calculations. The MRCI method with AVQZ and AV5Z basis sets is employed during the calculations. The artificial neural network is utilized to fit the analytical PES based on 28,552 energy points which are extrapolated to the complete basis set limit. The reaction dynamics of the O + LiH+ ⟶ Li+ + HO reaction is investigated by means of quasi-classical trajectory method. The dynamics results show that the reaction mechanism dominating the title reaction changes from indirect to direct mechanism with increasing collision energy. [ABSTRACT FROM AUTHOR]

Abstract 1-(N,N-dimethylamino)-1-silacyclohexane 1 was synthesized. Contributions of the conformers of 1, Eq- trans : Eq- gauche : Ax- trans , were found to be 55(15):15(15):30(15) mol.% in gas phase at 288 K from gas electron diffraction. The enthalpy Δ H = 0.29(15) kcal/mol for Ax-to-Eq transition was measured by temperature dependent Raman spectroscopy of liquid 1 and its solutions. Geometry, conformational properties and intramolecular conversion were explored by theoretical calculations. The nitrogen bond configurations for 1 was found to be close to planar, with a sum of the bond angles of ca. 350-355° that is quite different from those analogs in which the N atom is connected to a carbon atom rather than to a silicon atom. Graphical abstract Image 1 Highlights • Axial and equatorial conformers contribute to1-NMe 2 -1-silacyclohexane. • Equatorial conformers dominate in gas and liquid phases. • The substituent may occupy trans –and gauch -orientations. • Nitrogen bond configuration is of low pyramidality. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • Acetic acid decomposition over bare and MgO supported Ru catalyst studied by DFT. • OH cleavage path is favourable over both catalysts for acetic acid decomposition. • Ru/MgO performs better than bare Ru for acetic acid decomposition. • Kinetic parameters presented over wide range of temperature conditions. Abstract In this study, the decomposition of acetic acid to lower fraction products (i.e., CH 4 , CH 3 CHO, CO, and CO 2) is elucidated using different possible pathways along with their potential energy surfaces under density functional theory (DFT) framework. Furthermore, a kinetic investigation involving evaluations of rate constants, Arrhenius constants and equilibrium rate constants of all elementary reaction steps is carried out at a wide range of temperature (298–698 K) and a fixed pressure of 1 atm. Briefly, results indicate that overall decomposition of acetic acid is favourable through OH cleavage reaction route over both catalyst clusters involving elementary reaction steps of OH cleavage of acetic acid, CO cleavage of acetyl species, and hydrogenation of methyl to produce methane. The decomposition of acetic acid over both catalysts is highly likely to produce methane and CO 2 rather producing acetaldehyde which agrees with the existing experimental results. The formation of water from hydrogenation of hydroxyl group is not favourable over both catalyst clusters especially Ru/MgO catalyst. According to the kinetic investigation, the performance of supported Ru catalyst, i.e., Ru/MgO is superior to that of bare Ru catalyst for the decomposition of acetic acid. [ABSTRACT FROM AUTHOR]

A new accurate ab initio potential energy surface (PES) of the HeTiO system is constructed. The multi-reference configuration interaction with the Davidson correction is used to obtain the energy points, and the neural network method is employed to fit the PES. State-to-state rotational quenching cross sections and rate coefficients are obtained over a wide range based on the PES. Wigner threshold law is proved to be valid in the ultralow energy regime. In comparison with 3 He, 4 He is more efficient for the TiO molecule cooling process in the dominant transition j  = 1 → 0 due to the isotope effect. [ABSTRACT FROM AUTHOR]

In this work, we have constructed a high dimensional neural network (NN) potential energy function for simulating palladium surface properties. The NN potential was trained with 3035 density functional theory (DFT) calculations, and was shown to be nearly as accurate as DFT in molecular simulations. Important properties including lattice constants, elastic properties and surface energies as well as transition state energies and adatom diffusion barriers were predicted by the NN and were found to be in excellent agreement with DFT results. The computational time to run the NN was compared to DFT calculation time, and we found this implementation of the NN is roughly four orders of magnitude faster than DFT. This approach is general and applicable to other systems and may have applications in modeling catalytic processes at surfaces. [ABSTRACT FROM AUTHOR]

The double excited state intramolecular proton transfer (ESIPT) mechanisms of porphycene, were theoretically studied. The primary bond lengths, IR vibrational spectra and hydrogen-bond energy indicate that the intramolecular hydrogen bonds were strengthened in the first excited state, which facilitate the ESIPT processes. To elucidate the proposed mechanism, the potential-energy surfaces of the ground state and first excited state were constructed as functions of N H bond lengths and its relative torsional angle rotation. The intramolecular proton transfer of prophycene is more likely to occur through lengthwise pathway and proceed in the concerted coordinated transfer manner. [ABSTRACT FROM AUTHOR]

Molybdenum (Mo) nanoparticles (NPs) are one of the most effective refractory catalysts for preparing single-walled carbon nanotubes (SWCNTs) with high chirality. In this work, the evolution of Mo NPs at the initial stage of catalytic growth of SWCNT was investigated. It was found that NPs underwent transformation between the solid and semi-liquid phases during gradual deposition of C atoms, even though the deposition temperature was far below the melting point of NPs. Such transformation was caused by the elastic strain in NPs that could be manipulated by carbon (C) atoms. Furthermore, the results indicated that the lifetime of NPs in the semi-liquid state could be controlled by adjusting the feeding rate of C atoms. This work not only provides useful insight into the evolution of Mo NPs during the early stage of the catalytic growth of SWCNTs, but also opens up new prospects for controlling the lifetime of NPs in the semi-liquid phase by changing the experimental parameters. [Display omitted] [ABSTRACT FROM AUTHOR]

Recently, a new fluorescent chromophore 6,6′-((1E,1′E)-hydrazine-1,2-diylidenebis(methanylylidene))bis(3-(diethylamino)phenol) (DEASH) with double intramolecular hydrogen bonds (IHBs) was synthesized and could be used as an effective indicator of hydrazine. The experimental results showed that DEASH could emit bright green fluorescence due to the excited state intramolecular proton transfer (ESIPT) induced by IHBs. [ Dyes Pigments , 2022, 197, 109880.] However, the underlying mechanism of the ESIPT process for DEASH is still unclear. In this paper, we investigate excited-state intramolecular single (ESISPT) and double (ESIDPT) proton transfer processes of DEASH by density functional theory (DFT) and time-dependent density functional theory (TD-DFT) methods. Through the theoretical analyses for the constructed potential energy surfaces (PESs), excited hydrogen bond strengthening and photophysical properties of the molecule, we finally come to the conclusion that ESIDPT process of the DEASH in water solution is inclined to a stepwise process. [ABSTRACT FROM AUTHOR]

[Display omitted] • There are the negative correlations between the solvent polarities and the ESIPT processes as well as nπ* ICT. • There are the negative correlations between the solvent polarities and the tautomer emission as well as ππ* ICT. • The ESIPT reaction of 3NTF molecule is an ultrafast photochemical reaction less than 180 fs with dynamic simulation. • Compared with 3NHF isomer, the 3NTF isomer has the more nπ* character in the electron transition process. Recently, the dual-fluorescent phenomena of excited state intramolecular thiol proton transfer (ESIPT) for 3-thiolflavone derivative (3NTF) were reported by Chou and coworkers for the first time [ J. Am. Chem. Soc. 143 (2021) 12715 – 12724 ], which opened a new chapter in the field of ESIPT. Based on density functional theory (DFT) and time-dependent density functional theory (TDDFT), the proton transfer processes of 3NTF in toluene, dichloromethane and acetonitrile were studied. By optimizing the structure of the ground (S0) state and first excited (S1) state of 3NTF in different solvents, the hydrogen-bond parameters and proton-transfer potential energy curves were calculated. It was shown that although photo-excitation enhanced the intramolecular hydrogen bonding strength and thus promoted the occurrence of ESIPT, the solvent polarities inhibited the enhancement of the hydrogen bond of S1 state, which was not conducive to ESIPT. The electron spectra analyses were consistent with experimental data, which confirmed the rationality of molecular configurations. The time-evolved excited state dynamics simulation was performed based on the optimized structure of 3NTF, indicating that the ESIPT was an ultrafast photochemical reaction less than 180 fs. Moreover, we compared the potential energy surfaces of ESIPT, electronic structures based on natural transition orbitals (NTOs) method and electron-hole isosurfaces for the 3NTF and the traditional flavone molecule (3NHF), concluded that the unusually large Stokes shift fluorescence of 3NTF was mainly caused by the coupling of ESIPT and twisting intramolecular charge transfer (TICT), and the 3NTF isomer had the more nπ* character in the electron transition process. The nπ* ICT significantly increased with the decrease of solvent polarities, affecting the molecular photophysical properties, this made it more widely used in biomedical, photochemical, materials science and other fields. [ABSTRACT FROM AUTHOR]

• The API of Enzalutamide (ENZ) was synthesized via a milder condition in the presence of a new catalyst, and under the aerobic condition. • The mechanism of the reaction, especially the role of DMSO in this process has been investigated by the potential energy surface (PES) study. • The pharmaceutical analytical analyses were described and done for the API of ENZ. This paper has been prepared to investigate the question " why the five-membered ring formation to give Enzalutamide, needs at least a portion of dimethyl sulfoxide (DMSO) as the solvent and a high level of temperature about 95 ° C? ". By understanding the role of DMSO as solvent in the mechanism of such ring closing, this question might be answered. In addition, with the aid of the potential energy surface (PES) (dE) calculations, and the density functional theory (DFT) investigations, the PES curves of the reaction were designed to find the probable energy valleys and barriers of the process. The results of the experimental as well as theoretical studies showed that by choosing a suitable catalyst in DMSO: Isopropyl acetate (IPOAC) as the solvent mixture, we could handle the synthesis of Enzalutamide anti-cancer active pharmaceutical ingredient (API) in a milder condition with a lower temperature (about 70 °C), and also a shorter time (about 18 h instead of 24 h). Also, the developed HPLC-UV method showed that after crystallization, the API powder would have a total purity profile up to 99%. [Display omitted] [ABSTRACT FROM AUTHOR]

Methanimine reaction with O 2 on singlet and triplet potential energy surfaces are investigated using B3PW91, M06-2X, MP2 and CCSD(T) methods. Thermodynamic and kinetic parameters are calculated at M06-2X method. The most favorable channel involves H-abstraction of CH 2 NH+O 2 to the formation of HCN + H 2 O 2 products via low level energy barrier. The catalytic effect of water molecule on HCN + H 2 O 2 products pathway are investigated. Result shows that contribution of water molecule using complex formation with methanimine can decreases barrier energy of transition state and the reaction rate increases. Also, substituent effect of fluorine atom as deactivating group are investigated on the main reaction pathway. [ABSTRACT FROM AUTHOR]