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Interanion hydrogen bonding (IAHB) and halogen bonding (IAXB) have emerged as a counterintuitive linker in a range of fascinating applications. Despite the overall repulsive (positive) binding energy, anions are trapped in a local minimum with its corresponding transition state (TS) preventing dissociation. In other words, the adduct of anions is metastable. Seemingly, the electrostatic paradigm and force field description of hydrogen/halogen bonding (HB/XB) are challenged, because of the preconceived Coulombic repulsion. Aiming at an insightful understanding of these interanion phenomena, we employed the energy decomposition approach based on the block-localized wavefunction method (BLW-ED) to investigate a series of exemplary interanion complexes. As expected, the key distinction from the conventional HB/XB lies in the electrostatic interaction, which is not increasingly repulsive as anions gradually approach to each other. Rather, there is a Coulombic barrier at a certain point. After this point, the electrostatic repulsion diminishes with the decreasing distance between anions. Differently, other energy components vary monotonically just like in conventional cases. The nonmonotonic characteristic of the electrostatic interaction in interanion complexes was reproduced using the multipole expansion in AMOEBA polarizable force field in which the state-specified atomic multipoles were adopted. This suggests that the nonmonotonicity can be well interpreted by classical electrostatic theory and there is no conceptual difference between conventional HB/XB and IAHB/IAXB. The stability of IAHB/IAXB depends on the competition between the local attractive HB/XB and the global Coulombic repulsion of net charges, though there is cooperativity between these two contrasting forces. This concise model was supported by the attractive IAHB/IAXB in modified molecular capsules, which exhibit strong quadruple HB/XBs and a considerable distance between charged substituents.

The photodissociation of methyl hydroperoxide (CH3OOH) at 193 nm has been studied using a direct dynamics trajectory surface-hopping (TSH) method. The potential energies, energy gradients, and nonadiabatic couplings are calculated on the fly at the MRCIS(6,7)/aug-cc-pVDZ level of theory. The hopping of a trajectory from one electronic state to another is decided on the basis of Tully's fewest switches algorithm. An analysis of the trajectories reveals that the cleavage of the weakest O-O bond leads to major products CH3O(2E) + OH(2Π), contributing about 72.7% of the overall product formation. This OH elimination was completed in the ground degenerate product state where both the ground singlet (S0) and first excited singlet (S1) states become degenerate. The O-H bond dissociation of CH3OOH is a minor channel contributing about 27.3% to product formation, resulting in products CH3OO + H. An inspection of the trajectories indicates that unlike the major channel OH elimination, the H-atom elimination channel makes a significant contribution (∼3% of the overall product formation) through the nonadiabatic pathway via conical intersection S1/S0 leading to ground-state products CH3OO(X 2A″) + H(2S) in addition to adiabatic dissociation in the first excited singlet state, S1, correlating to products CH3OO(1 2A') + H(2S). The computed translational energy of the majority of the OH products is found to be high, distributed in the range of 70 to 100 kcal/mol, indicating that the dissociation takes place on a strong repulsive potential energy surface. This finding is consistent with the nature of the experimentally derived translational energy distribution of OH with an average translational energy of 67 kcal/mol after the excitation of CH3OOH at 193 nm.

Based on the new 2A' and 4A' potential energy surfaces of NO2 fitted by Varga et al., we conducted a quasi-classical trajectory study on the N(4S) +O2(X3Σg- ) → NO(2Π) + O(3P) reaction, focusing on the high vibrational state up to ν = 25. For different rovibrational states of O2, within the relative translational energy (Ec) range of 0.1-30 eV, the total exchange cross section (ECS) is calculated, and it is found that the initial relative translational energy and vibration excitation have a significant effect on ECSs, while rotational excitation has little influence; the rate coefficient of the high rovibrational state of O2 molecules at high temperatures is studied, and it is found that when the vibrational level ν of O2 is in the range of 0-15, the value of log10k(T, ν, j) with the vibrational level ν is almost linear, while when ν is greater than 15, it becomes gentle with the increase in ν. Finally, the state-to-state rate coefficients are calculated; our results supply the advantageous state-to-state process data in the NO2 system, and they are useful for further studying the related hypersonic gas flow at very high temperature.

In this work, radical anion photodetachment photoelectron (PD-PE) spectra of N-methylacridone (NM-AC) and N,N'-dimethyl-trans-quinacridone (NNM-QAC) are presented, from which we derived electron affinities and transition energies from S0 to the lowest excited triplet and singlet states (T1, T2, and S1). Because in molecules with extended π systems and heteroatoms the state density even in the energy range of the lowest excited electronic states is already high, assignment of most of the spectral structures in the PD-PE spectra was possible only on the basis of theoretical calculations. To this end, adiabatic transition energies including zero-point vibrational energy corrections were determined using a combination of density functional theory, time-dependent density functional theory, and multireference configuration interaction methods. Calculated Franck-Condon spectra proved to be particularly valuable for the assignment of the spectra. Surprisingly, the density of electronically excited states in the low-energy regime is smaller for NNM-QAC than for NM-AC. This is due to the fact that the nπ* energies remain nearly the same in the two molecules whereas the lowest ππ* excited singlet and triplet transitions are strongly red-shifted in going from NM-AC to NNM-QAC.

We use molecular dynamics to calculate the rotational and vibrational energy relaxation of C2H6 in Ar, Kr, and Xe bath gases over a pressure range of 10-400 atm and at temperatures of 300 and 800 K. The C2H6 is instantaneously excited by 80 kcal/mol randomly distributed into both vibrational and rotational modes. The computed relaxation rates show little sensitivity to the identity of the noble gas in the bath. Vibrational relaxation rates show a nonlinear pressure dependence at 300 K. At 800 K the reduced range of bath gas densities covered by the range of pressures does not yet show any nonlinearity in the pressure dependence. Rotational relaxation is characterized with two relaxation rates. The slower rate is comparable to the vibrational relaxation rate. The faster rate has a linear pressure dependence at 300 K but an irregular, nonlinear pressure dependence at 800 K. To understand this, a model was developed based on approximating the periodic box used in the molecular dynamics simulations by an equal-volume collection of cubes where each cube is sized to allow only single occupancy by the noble gas or the molecule. Combinatorial statistics then leads to a pressure- and temperature-dependent analytic distribution of the bath gas species the molecule encounters in a collision. This distribution, the dissociation energy of molecule/bath gas complexes and bath gas clusters, and the computed energy release per collision combine to show that only at 300 K is the energy release sufficient to dissociate likely complexes and clusters. This suggests that persistent and pressure-dependent clusters and complexes at 800 K may be responsible for the nonlinear pressure dependence of rotational relaxation.

The electronic g-tensor calculations are performed for dangling bonds (DBs) introduced into nanodiamonds (NDs) with four different functional groups on their surfaces. For hydrogenated and fluorinated NDs, it is found that g-shifts of the latter vary in a much wider range, and the same is also true for the total energy differences between the highest and the lowest energy DBs. In addition, it is shown that the shape of NDs significantly impacts the energetics and g-shifts of DBs, whereas the influence of the size is much less pronounced, as is the influence of the presence of one DB in the vicinity of the other, resulting in no substantial change on their magnetic behavior. For hydroxylated and aminated NDs, it is demonstrated that the variation range of g-shifts is larger for the former, whereas the opposite is seen regarding the total energy differences. On the whole, some of the positions of DBs can be energetically very costly in these NDs; besides, the lowest energy DBs are irregular, that is, formed by OH- and NH2-bonded C atoms, contrasting with hydrogenated and fluorinated NDs, for which irregular DBs are the most energetically unfavorable.

The fast F reaction with NH3 poses a big challenge to experimental studies because of secondary chemical and collisional reactions. The quasi-classical trajectory method is utilized to investigate the mode specificity, product energy disposal, and temperature dependence of the thermal rate coefficient of F + ND3 → DF + ND2 on a recently developed potential energy surface. The effect of isotopic substitution is explored by comparing the F + ND3 reaction with the F + NH3 reaction. The computed results permit a better understanding of the F + ammonia reaction. The DF vibrational state has a Λ-type distribution, in accordance with the experimental measurement by the fast flow reactor technique. The product ND2 is dominantly populated in the ground state, and a considerable amount of ND2 is produced in the fundamental states of the bending mode. The similar vibrational state distributions of HF and NH2 in the F + NH3 reaction indicate a weak isotopic substitution effect on the product energy disposal. Exciting the umbrella mode of ND3 suppresses the reaction at low energies below 5 kcal mol-1, in sharp contrast to the observation in the F + NH3 reaction. These dynamical behaviors can be partially explained by the sudden vector projection model. In addition, the thermal rate coefficient of F + ND3 shows no temperature dependence in the range between 150 and 2000 K. There exists an inverse kinetic isotope effect at temperatures from 150 to 1500 K.

There is an intense race by the scientific community to identify materials with potential applications for the conversion of carbon dioxide (CO2) into new products. To extend the range of possibilities and explore new effects, in this work, we employ density functional theory calculations to investigate the presence of edge effects in the adsorption and activation of CO2 on pristine and Fe-decorated (WS2)16 nanoflakes. We found that Fe has an energetic preference for hollow sites on pristine nanoflakes, binding with at least two two-fold edge S atoms and one or two three-fold core S atoms. Fe adsorption on the bridge sites occurs only at the edges, which is accompanied by the breaking of W-S bonds in most cases (higher energy configurations). CO2 activates on (WS2)16 with an OCO angle of about 129° only at higher energy configurations, while CO2 binds via a physisorption mechanism, linear structure, in the lowest energy configuration. For CO2 on Fe/(WS2)16, the activation occurs at lower energies only by the direct interaction of CO2 with Fe sites located near to the nanoflake edges, which clearly indicates the enhancement of the catalytic activity of (WS2)16 nanoflakes by Fe decoration. Thus, our study indicates that decorating WS2 nanoflakes with TM atoms could be an interesting strategy to explore alternative catalysts based on two-dimensional materials.

The thermal unimolecular decomposition of a methoxy radical (CH3O), a key intermediate in the combustion of methane, methanol, and other hydrocarbons, was studied using high-level coupled-cluster calculations, followed by E,J-resolved master equation analyses. The experimental results available for a wide range of temperature and pressure are in striking agreement with the calculations. In line with a previous theoretical study that used a one-dimensional master equation, the tunneling correction is found to exhibit a marked pressure dependence, being the largest at low pressure. This curious effect on the tunneling enhancement also affects the calculated kinetic isotope effect, which falls initially with pressure but is predicted to rise again at high pressures. These findings serve to reconcile a set of conflicting results regarding the importance of tunneling in this prototype unimolecular reaction and also motivate further experimental investigation. This study also exemplifies how changes in the energy redistribution due to collisions manifest in the tunneling rates.

In radionuclide compounds undergoing electron capture (EC) decay, the electron density at the nucleus (ρ(0)) and half-life of the nucleus are inversely proportional. Thus, the decay can be accelerated by changing the chemical or physical conditions. A previous study reported a 1.1-1.5% reduction in the half-life of 7Be encapsulated in C60 compared with 7Be metal. However, 7Be was inserted into the fullerene using the rebound energy of the nuclear reaction, which may not be a practical method. This paper elucidates the mechanism of ρ(0) change in various Be compounds from density functional calculations and attempts to propose better systems that show faster EC decay (larger ρ(0)) and/or that are easier to generate than Be in C60. In typical Be compounds, ρ(0) decreases because Be donates electrons to other atoms through chemical bonds and, thus, is not effective. Among the various Be-encapsulated fullerenes (C20-C180), the largest increase in ρ(0) was obtained for C50 fullerene, but the magnitude was almost similar to that of C60. As new systems, we propose Be-encapsulated rare gas solids, which would be generated only by applying high pressure. An increase in ρ(0) from Be metal in the range 2-10%, which depends on the lattice constant, is obtained.

A full-dimensional global potential energy surface (PES) for the KRb + KRb → K2Rb2* → K2 + Rb2 reaction is reported based on high-level ab initio calculations. The short-range part of the PES is fit with the permutationally invariant polynomial-neural network method, while the long-range parts of the PES in both the reactant and product asymptotes are represented by an asymptotically correct form. The long- and short-range parts are connected with intermediate-range parts to make them smooth. Within a statistical quantum model, this PES reproduces both the measured loss rates of ultracold KRb molecules and the K2 and Rb2 product state distributions, underscoring the important role of tunneling in ultracold chemistry. The PES also correctly predicts the lifetime of the K2Rb2* intermediate complex within the Rice-Ramsperger-Kassel-Marcus limit. It thus provides a reliable platform for future dynamical studies of the prototypical reaction.

The acidity of acetylene CH is stronger than that of alkane CH, and the attractive interaction between an acetylene CH with π-electrons, which shows a clear hydrogen bond property, is called activated CH/π interaction. In this study, cooperative enhancement of the activated CH/π interaction has been probed through the cluster size dependence of the red shift of the acetylene CH stretching vibrational band in neutral phenol-(acetylene)n (∼16 ≤ n ≤ ∼30) and (acetylene)n+ (10 ≤ n ≤ 70). In both the clusters, the characteristic asymmetric (red-shaded) shape of the CH stretch band has been observed. This band shape means that the magnitude of the activated CH/π interaction is enhanced by its cooperativity in the interior moiety of the cluster. The red-shifted component of the band extends with increasing cluster size, and the edge of this component seems to reach to the CH stretch band position of crystalline acetylene at the size of n = 20-30, indicating that dozens of molecules need to interact each other to maximize cooperativity in the activated CH/π interaction of acetylene. On the other hand, the peak position of the band does not converge to that of crystalline acetylene in the observed size range. The present result suggests that the spectral convergence of acetylene clusters to the bulk may occur in the cluster size range of hundreds or larger.

To clarify the contentions about dissociative photoionization mechanism of nitrogen dioxide via the a3B2 and b3A2 ionic states, a new threshold photoelectron-photoion coincidence (TPEPICO) velocity imaging has been conducted in the 12.8-14.0 eV energy range at the Hefei Light Source. The fine vibrational-resolved threshold photoelectron spectrum agrees well with the previous measurements. The ro-vibrational distributions of NO+, as the unique fragment ion in the dissociation of NO2+ in specific vibronic levels of a3B2 and b3A2 states, are derived from the recorded TPEPICO velocity images. A "cold" vibrational (v+ = 0) and "hot" rotational population is observed at the a3B2(0,3,0) and (0,4,0) vibronic levels, while the dissociation of NO2+ in b3A2(0,0,0) leads to the NO+ fragment with both hot vibrational and rotational populations. With the aid of the quantum chemical calculations at the time-dependent B3LYP level, minimum energy paths on the potential energy surfaces of the a3B2 and b3A2 states clarify their adiabatic dissociation mechanisms near the thresholds, and this study proposes reliable explanations for the observed internal energy distributions of fragment ions. Additionally, this study provides valuable insights into the application of the classical "impulsive" model on an overall slow dissociation process.

Organic aerosol can adopt a wide range of viscosities, from liquid to glass, depending on the local humidity. In highly viscous droplets, the evaporation rates of organic components are suppressed to varying degrees, yet water evaporation remains fast. Here, we examine the coevaporation of semivolatile organic compounds (SVOCs), along with their solvating water, from aerosol particles levitated in a humidity-controlled environment. To better replicate the composition of secondary aerosol, nonvolatile organics were also present, creating a three-component diffusion problem. Kinetic modeling reproduced the evaporation accurately when the SVOCs were assumed to obey the Stokes-Einstein relation, and water was not. Crucially, our methodology uses previously collected data to constrain the time-dependent viscosity, as well as water diffusion coefficients, allowing it to be predictive rather than postdictive. Throughout the study, evaporation rates were found to decrease as SVOCs deplete from the particle, suggesting path function type behavior.

We report an ion velocity imaging study of the charge exchange reactions between Ar+ ion and trans-/cis-dichloroethylene in the collision energy range of 2.1-9.5 eV, and we find that the energy-resonant charge transfer plays a dominant role in the large impact-parameter reaction. The parent yields C2H2Cl2+ in the high-lying excited states are directly produced in the charge exchange reactions, while they prefer spontaneous fragmentations in photoionization. This significant difference indicates that the present charge exchange reactions are much slower than the photoelectron detachment. The structural relaxations of the target molecule are allowed in multiple dimensions of freedom during the charge transfer, which should be frequently observed for the charge exchange reactions with large molecules.

Focused electron beam deposition often requires the use of purification techniques to increase the metal content of the respective deposit. One of the promising methods is adding H2O vapor as a reactive agent during the electron irradiation. However, various contrary effects of such addition have been reported depending on the experimental condition. We probe the elementary electron-induced processes that are operative in a heterogeneous system consisting of iron pentacarbonyl as an organometallic precursor and water. We use an electron beam of controlled energy that interacts with free mixed Fe(CO)5/H2O clusters. These mimic the heterogeneous system and, at the same time, allow direct mass spectrometric analysis of the reaction products. The anionic decomposition pathways are initiated by dissociative electron attachment (DEA), either to Fe(CO)5 or to H2O. The former one proceeds mainly at low electron energies ( 6 eV), where the DEA to H2O forms OH- in the first reaction step. This intermediate reacts with Fe(CO)5, leading to enhanced decomposition, with the desorption of up to three CO ligands. The present results demonstrate that the water action on Fe(CO)5 decomposition is sensitive to the involved electron energy range and depends on the hydration degree.

Several mechanisms for the electropolymerization of pyrrole have been proposed since the first report 40 years ago. However, none of them were consensual despite a range of assumptions. We simulated and explained the preliminary steps governing the electropolymerization of pyrrole in a charged model interface using first-principles molecular dynamics calculations to solve the problem. We have shown under these conditions that adjacent pyrrole molecules in water can react together, causing their electropolymerization at the interface with a biased platinum electrode in anodic oxidation. In this work, the effective screening medium method that prevents energy divergence of the system was applied to different configurations of pyrrole, water, and electrolyte molecules to best screen the phase space. Furthermore, we worked on a Pt(100) electrode surface in an aqueous electrolyte to be as close as possible to the experimental conditions, MD taking the average of their different orientations.

The OH + NO_2 reaction is a critically important process for radical chain termination in the atm. with a major impact on the ozone budgets of the troposphere and stratosphere. Rate consts. for the reaction of OH + NO_2 + → products have been measured under conditions relevant to the upper troposphere/lower stratosphere with a Pulsed Laser Photolysis - Pulsed Laser Induced Fluorescence technique augmented by in situ optical spectroscopy for quantification of [NO_2]. The expts. are carried out over the temp. range of 230K - 330K and the pressure range 40-800 Torr of air and N_2. The reaction was studied under pseudo first-order conditions, monitoring the decay of OH in the presence of a large excess of NO_2. The obsd. pressure and temp. dependences are analyzed to quantify the falloff behavior and to derive parameters for Troe falloff expressions. The atm. implications are discussed.

Quasiclassical trajectory computations are performed for the F- + CH3I(v = 0, JK) → I- + CH3F (SN2) and HF + CH2I- (proton-transfer) reactions considering initial rotational states characterized by J = {0, 2, 4, 6, 8, 12, and 16} and K = {0 and J} in the 1-30 kcal/mol collision energy (Ecoll) range. Tumbling rotation (K = 0) counteracts orientation effects, thereby hindering the SN2 reactivity by about 15% for J = 16 in the 1-15 kcal/mol Ecoll range and has a negligible effect on proton transfer. Spinning about the C-I bond (K = J), which is 21 times faster than tumbling, makes the reactions more direct, inhibiting the SN2 reactivity by 25% in some cases, whereas significantly enhancing the proton-transfer channel by a factor of 2 at Ecoll = 15 kcal/mol due to the fact that the spinning-induced centrifugal force hinders complex formation by breaking H-bonds and activates C-H bond cleavage, thereby promoting proton abstraction on the expense of substitution. At higher Ecoll, as the reactions become more direct, the rotational effects are diminishing.

Dynamics of the reaction of hydrogen sulfide, H2S(X1A1), with ground-state atomic carbon, C(3Pj), was investigated over the interpolated ab initio-based potential energy surface using the quasi-classical trajectory (QCT) simulation. The reaction probability and total reactive cross section were calculated at a wide range of collision energies from 2.6 to 78.8 kJ mol-1. The total rate constant of the reaction was calculated using collision theory. The energy distribution for the formation of main products (HCS/HSC + H) was also investigated. At 44.6 kJ mol-1 collision energy, approximately 39.5 and 12% of the total available energy were released to translational and rotational energy levels of the HCS + H products, respectively, while for HSC + H, these values were found to be about 61.6 and 25.7% of the total available energy. The remaining total energy was deposited in the vibrational modes of the products.

Quantifying vibronic couplings in molecular excited states is crucial for the elucidation of a broad range of photophysical phenomena. In this study, we compare different theoretical approaches for the calculation of reorganization energy, a measure of vibronic coupling strength, and provide a rigorous derivation to show that molecular transition density characterizing electron-hole excitation could be used to quantify the magnitude of reorganization energy. The theory enables a descriptor based on molecular-orbital coefficients and atomic transition densities to quantify the magnitude of reorganization energies in molecular excited states. Applying the approach to low-lying excited states of polyacenes, we demonstrate that transition density distribution explains the difference in the magnitude of the reorganization energy of different excited states. Furthermore, to clarify the applicability of the transition density descriptor in molecular design for small-reorganization energy molecules, we investigate a broad range of molecular chromophores to show the effectiveness of the proposed theory. With this perspective on the relationship between reorganization energy and transition density, we successfully provide a quantitative rule to identify π-conjugated systems with small reorganization energy in the excited state, which should be useful for the development of novel optoelectronic materials.

We present an experimental and theoretical investigation of the photon interaction with formic acid in the vacuum-ultraviolet energy range. The absolute absorption cross sections and ionization efficiencies were measured in the 11.2-21.4 and 13.5-21.4 eV ranges, respectively, using a double-ion chamber technique. Photoionization and neutral-decay cross sections were derived from these results. From the present ionization cross sections and previously reported ionic dissociative branching ratios, the partial cross sections for dissociating processes were obtained. Theoretically, the photoionization cross sections and the asymmetry parameters of the photoelectron angular distributions for ionization out of the six outermost valence orbitals (10

Sulfuryl fluoride (SO2F2) plays an important role in the operation of gas-insulated switchgear (GIS) equipment where it is widely used as the characteristic gas for discharge diagnostics. However, the formation mechanism of SO2F2 is currently unclear, and as a consequence, we have employed a range of ab initio methods to investigate the hydrolysis reaction of SOF4 that is known to afford SO2F2 in the gas phase. These results suggest that two H2O molecules are incorporated into a low energy transition state to afford an H-bond network that facilitates proton transfer during the hydrolysis of SOF4.

In photocatalysis, it is of general interest to understand and design wide-range light-absorbing inorganic/organic hybrid materials with an excellent photo-induced intramolecular charge-transfer (ICT) effect. To verify the role of unpaired electrons in enhancing ICT within electron-withdrawing ligand-based metal-organic frameworks (MOFs), the molecular structure, density of states (DOS), and electronic structure of strong electron-deficient pyridine-diketopyrrolopyrrole (

Ion-molecule charge-exchange reactions Ar+ + CO → Ar + CO+ at the center-of-mass collision energies of 4.40, 6.40, and 8.39 eV are investigated using ion velocity map imaging technique. Although multiple electronically excited states of CO+ are accessed, the population of CO+ at the A2Π state is predominant in the present collision-energy range. In contrast to our previous study for NO, but similar to the case of O2, the forward-scattered CO+ yields show a broader angular distribution at the higher collision energy. Typically, the Franck-Condon-region charge transfer, energy resonant charge transfer, and intimate collision are three different mechanisms in which the intimate collision experiences an intermediate complex, and this mechanism usually plays an essential role in the thermal-energy reactions. However, the present observations indicate that this mechanism, concerning the intermediate (Ar-CO)+, is still of utmost importance in a relatively high collision-energy range.

Rotationally resolved spectra of the H3Σu- - X3Σg- electronic transition bands of Si2 have been experimentally studied using laser induced fluorescence in the 380 - 520 nm range. Si2 molecules are ...

The anion photoelectron imaging spectra of an ion with m/z 85, generated under ion source conditions that optimize ·OH production in a co-expansion with isoprene, are presented and analyzed with supporting calculations. A spectroscopic feature observed at a vertical electron detachment energy of 2.45 eV, which dominates the photoelectron spectrum measured at 3.495 eV photon energy, is consistent with the OH−·isoprene ion-molecule complex, while additional signal observed at lower electron binding energy can be attributed to other constitutional isomers. However, spectra measured over a 2.2 to 2.6 eV photon energy range, i.e., from near threshold of the predominant OH−·isoprene detachment feature through the vertical detachment energy, exhibit sharp features with common electron kinetic energies, suggesting autodetachment from a temporary anion prepared by photoexcitation. The photon energy independence of the electron kinetic energy of these features along with the low dipole moment predicted for the neut...

Structural evolution and stability pattern of pure neutral gold clusters Aun in the small size range of n = 20–30 are examined using density functional theory (DFT) calculations. The equilibrium ge...

International audience; The behavior of potential prebiotic species in space is of main concern in the chemistry at the origin of life. Their reactivity or stability in spatial conditions, under strong UV radiations or ion bombardments, remains an open question and needs wide investigations. As protons are by far the most abundant ions in space, we focus presently on proton-induced collisions on imidazole and 2-aminoimidazole evidenced as important prebiotic RNA intermediates. Unconstrained full optimization of the structures was performed with B3LYP/cc-pVTZ model chemistry. The calculations were performed in a wide collision energy range in order to model various astrophysical environments, from eV in the interstellar medium, up to keV for solar winds or supernovae shock-wave protons. Such a study provides for the first time a theoretical insight on the influence of the amino substituent on the proton-induced charge transfer. We evaluated the role of icy grain environments through a cluster approach modeling the effect of a stepwise microhydration on the process. Comparisons with oxygenated and sulfurated analogues address further qualitative trends on the respective stability or reactivity of such heterocycles which may be of tremendous interest in prebiotic chemistry. Charge transfer appears to be quite efficient for imidazole compounds and their sulfurated analogue compared to the oxygenated heterocycle.

In the present work, the optical response of isolated (CdSe)n+ clusters with n = 3–6 is probed by measuring the photodissociation cross section in the photon energy range ℏω = 1.9–4.9 eV. In this j...

We present a study of the structural evolution of palladium cluster anions in a size range from 55 to 147 atoms using a combination of trapped ion electron diffraction and density functional theory computations. We show that Pdn- clusters (n = 55, 65, 75, 85, 95, 105, and 147) change from an icosahedral motif at Pd55- to the bulk fcc motif at Pd147-. This size-dependent structure transition is probed experimentally at a temperature of 95 K and characterized by a continuously increasing fraction of fcc isomers over the considered size range showing a crossover to the fcc motif at n ≈ 90.

High-resolution velocity map imaged photoelectron spectra of the nitrite anion NO2– are measured over a range of photodetachment wavelengths between 355 and 550 nm, resolving the vibrational and ro...

The interactions between a wide variety of molecules having σ-holes or π-holes and several nitrogen bases have been analyzed computationally. The σ- and π-hole atoms span groups III–VII of the periodic table. The interaction energies range from quite weak, typical of non-covalent bonding, to unusually strong: from −4.6 to −22.0 kcal/mol for σ-hole bonding and from −4.0 to −42.4 kcal/mol for π-hole bonding. The markedly greater strengths of some bonds does not imply that any new factors or types of bonding are involved; they simply reflect higher degrees of the polarization that is part of any Coulombic interaction. To explain the stronger bonding, this polarization must be explicitly taken into account. We show that the interaction energies can be related quite well to (a) the maximum positive electrostatic potentials associated with the σ- or π-holes on their molecular surfaces, (b) the polarizabilities of the nitrogen bases, and especially (c) the polarizing electric fields of the σ- or π-hole molecules...

Recent experimental data reveal the complexity of diffusion dynamics beyond the scope of classical Brownian dynamics. The particles exhibit diverse diffusive motions from the anomalous toward classical diffusion over a wide range of temporal scales. Here a dressed diffusion model is developed to account for non-Brownian phenomena. By coupling the particle dynamics with a local field, the dressed diffusion model generalizes the Langevin equation through coupled damping kernels and generates the salient feature of time-dependent diffusion dynamics reported in the experimental measurements of biomolecules. The dressed diffusion model provides one quantitative aspect for future endeavors in this rapid-growing field.

Three-dimensional ion momentum imaging is developed in a combination of ion velocity map imaging technique and delay-line anode ion detection, and applied for the ion-molecule charge exchange reaction between Ar+ and CO2. In a center-of-mass collision energy range of 7.23 - 15.96 eV, CO2+ products are primarily populated at the ground state X2Πg and the single-electron excited states A2Πu, B2Σu+, and C2Σg+; the multi-electron excited states of CO2+ are also found at the higher collision energies. The production efficiency profiles of CO2+ are distinctly different from the photoionization electron spectrum of CO2, implying that the charge transfer from Ar+ would be not so fast as expected. The strong electron correlations in the short-lived intermediate (Ar-CO2)+ should be responsible for the CO2+ yields at the multi-electron excited states.

A quasiclassical trajectory study of the kinetics of the title astrochemical reaction in a range of temperatures varying from 5 to 1000 K (corresponding to both the outer and the inner regions of the protostar and the circumstellar envelopes) was carried out and a clear dependence of the rate coefficient on the temperature is given, in contrast with the constant value adopted in kinetics astrochemical databases. Levering the massive nature of the performed calculations and of the detailed dynamical investigation of the reactive process, a rationalization of the temperature dependence of the released translational energy and of the rovibrational population of the CH and H2 diatomic products is also provided. Furthermore, the effect of the initial rovibrational energy of CH2 on the state-specific rate coefficients and cross sections is analyzed in order to single out the role played by the different regions of the potential energy surface on the dynamical outcomes and on the modeling the temperature dependence of the reactive efficiency of the investigated process. This led to a parametrization of the computed rate in terms of the following double Arrhenius expression (in cm3 s-1), k(T) = 2.50 × 10-10 exp(- 1.67/T) + 5.98 × 10-11 exp(- 280.5/T), alternative to the piecewise formulation into the three subintervals of temperature in which the overall 5-1000 K interval can be divided.

The rate coefficients, k, for the gas-phase reaction of the OH radical and Cl-atom with (E)- and (Z)-CF3CF═CFCF3 were measured using a relative rate technique over a range of temperature (240–375 K...

Atmospheric organic aerosols comprise complex mixtures of a myriad of compounds with a wide range of structures and volatilities. To understand the fate of atmospheric organic aerosols and their contribution to particulate matter pollution, we need to study the relative portion divided between semivolatile organic compounds (SVOCs) and low-volatility organic compounds (LVOCs). SVOCs can effectively migrate and exchange between aerosol populations and thus are more accessible for further reactions and removal processes, while LVOCs will essentially stay in the particle phase. Here, we introduce using ionic liquid droplets as novel sorbents for organic vapors in smog chamber experiments to study the transfer of constituents between aerosol populations and to separate SVOCs and LVOCs from chamber-produced secondary organic aerosols (SOAs). SOA was formed and condensed on the ammonium-sulfate seeds, and later ionic liquid droplets were introduced into the chamber. We show that there are considerable yields of both LVOCs and SVOCs produced from α-pinene ozonolysis, and the uptake of SVOCs into the ionic liquid increases as the amount of reacted α-pinene increases. We also show that the SVOCs absorbed into the ionic liquid re-evaporate more readily compared to SOA originally condensed on the ammonium-sulfate seeds. We are thus able to differentiate the semivolatile components that partition into the extremely polar ionic liquid aerosols from the demonstrably less volatile components also condensed on the ammonium-sulfate seeds. Combined with previous studies using other organic aerosols as solvents to probe SVOC transfer between aerosol populations, we provide a wide set of measurements to probe and constrain the physical and thermodynamic properties of chamber-produced SOA complex.

International audience; A theoretical approach, in which the rotational degrees of freedom are treated quantum mechanically while translational degrees of freedom classically or semiclassically, is applied to calculate the total and final-state specific cross sections for the reaction H − + H → H 2 (v, j) + e − in the range of low collision energies (E = 1− 754 meV). The calculated cross sections agree well with the existing experimental and theoretical results. Results are also presented for the inverse dissociative attachment process: H 2 (v, j) + e − → H − + H.

Excimers play an important role in photochemical processes ranging from singlet fission to DNA damage, and the characteristic red-shift in fluorescence spectra associated with excimer formation can provide information about aggregate formation and the orientation of chromophores. When a mixture of chromophores is present, exciplex formation may lead to spectral characteristics distinct from those of either monomer or the corresponding excimers. To predict the effects of aggregation in a system containing a mixture of small acenes, binding energies and minimum-energy geometries have been calculated for three mixed S_1 exciplexes. Benchmark CASSCF/NEVPT2 multireference binding energies of 18.2, 27.7, and 49.3 kJ/mol are reported for the benzene-naphthalene, benzene-anthracene, and naphthalene-anthracene exciplexes, respectively. TDDFT calculations have been performed using a range of exchange-correlation functionals, showing that many functionals perform inconsistently, and the error in binding energy often depends on the character of the monomer excitation from which the exciplex state is derived. Moderate exciplex stabilization observed for the benzene-naphthalene and naphthalene-anthracene exciplexes results from a mixture of charge transfer and exciton delocalization.

We present a method based on kinetic molecular theory that identifies reactions of various molecularities in molecular dynamics (MD) simulations of bulk gases. The method allows characterization of the thermodynamic conditions at which higher than bimolecular reactions are a factor in the mechanisms of complex gas-phase chemistry. Starting with Bodenstein's definition of termolecular collisions we derive analytical expressions for the frequency of higher molecularity collisions. We have developed a relationship for the ratio of the frequencies of termolecular to bimolecular collisions in terms of the temperature, density, and collision times. To demonstrate the method, we used ReaxFF in LAMMPS to carry out MD simulations for NVT ensembles of mixtures of H2-O2 over the density range 120.2-332.7 kg m-3 and temperature range 3000-5000 K. The simulations yield ReaxFF-based predictions of the relative importance of termolecular collisions O2···H2···O2 and bimolecular collisions O2···H2 in the early chemistry of hydrogen combustion.

Broadband microwave spectra over the 2-18 GHz range have been recorded for the resonance-stabilized 2-furanyloxy radical, formed in the first step of pyrolysis of the second-generation biofuel 2-methoxyfuran by methyl loss. Using a flash pyrolysis source attached to a pulsed valve, a 0.7% mixture of 2-methoxyfuran in argon was pyrolyzed at a series of temperatures ranging from 300 to 1600 K. Subsequent cooling in a supersonic expansion produced rotational temperatures of ∼2 K in the interrogation region. Using chirped-pulse Fourier transform microwave (CP-FTMW) methods, combined with strong-field coherence breaking (SFCB), a set of transitions due to the radical were identified and assigned. The experimental rotational constants ( A = 8897.732(93), B = 4019.946(24), C = 2770.321(84)), centrifugal distortion constants, and spin-rotation coupling constants have been determined for the radical and compared with ab initio predictions at the CCSD(T) level of theory. Compared to the 2-methoxyfuran precursor, the 2-furanyloxy radical has allylic C-C bond lengths intermediate between single and double bonds, a shortened C(5)-O(6) bond characteristic of partial double-bond character, and an O(1)-C(5)-O(6) bond angle of 121°, which resembles the O-C-O angle of an ester. Atomic spin densities extracted from the calculations confirm that the 2-furanyloxy radical is best viewed as a carbon-centered allylic lactone radical, with 80% of the spin density on the two allylic carbons and 20% on the pendant O(6) atom.

The acidity dependence of the iron-catalyzed bromate-malonic acid Belousov–Zhabotinsky reaction was studied in the range 0.36 M < [H2SO4]0 < 1.20 M, and the temporal evolutions of the oscillation p...

A global potential energy surface (PES) representation of the C(3P) + SH(X 2Π) → H(2S) + CS(a 3Π) system is developed by fitting plenty of precise energies obtained through the ab initio calculation with aug-cc-pVQZ and aug-cc-pV5Z basis sets via extrapolation to the complete basis set limit. The topographical characteristics of the PES are examined in detail, and it is found that they agree well with previous calculations available in the literature. By utilizing the PES of HCS(A2A″), the corresponding reaction is investigated using the quasi-classical trajectory (QCT) method in the collision energy range of 0.08–1.0 eV. The minimum energy paths (MEPs) calculated on the basis of the present PES indicate that the C(3P) + SH(X 2Π) → H(2S) + CS(a 3Π) reaction is exothermic, with the exothermicity ∼0.204 eV. The calculation for the capture time indicates that the reaction is mainly governed by the indirect mechanism at the lower collision energy, while, for higher collision energy, the direct mechanism is in...

We systematically studied the adsorption of O2 on Aun– in the size range of 0–1 nm at low temperatures and determined new active sizes with n = 22, 24, 34, and 36. The kinetic measurements more clearly showed the correlation between the reactivity of Aun– with O2 and their electronic properties: the sizes with a closed electron shell are always inert, and the sizes with an unpaired electron can chemically adsorb one O2 molecule if their adiabatic detachment energies (ADEs) are lower than a threshold around 3.5 eV. This ADE threshold dividing the active and inert Aun– is independent of the clusters’ sizes, global geometries, and local adsorption sites. According to the widely accepted electron transfer mechanism, this threshold could stand for the case in which the total energy of the Aun– and an O2 roughly equals that of the spin crossover point of the potential surfaces of Aun–O2– and Aun–···O2.

Low-energy linear absorption spectrum of a series of 48 donor-acceptor-donor (D-A-D) scheme based thiophone-benzo(bis-)X-diazole molecules with X = O, S, Se, or Te are calculated using time dependent density functional theory in order to propose strategical design of molecules that can efficiently absorb light in the infrared and visible region of the solar spectrum. Our study establishes that optical properties of the D-A-D based organic molecules significantly depend on the donor-to-acceptor (D/A) ratio and the strength of the acceptor moiety. Thus, by choice of a suitable D/A ratio and type of the acceptor moiety, the linear absorption spectrum can be largely shifted, in general, while the optical gap can be engineered over a wide energy range of ∼0.2-2.3 eV, in particular. It is also noticed that the increase in acceptor units (i.e., when D/A ≤ 1) leads to increase in steric hindrance in between them. This, in turn, disrupts the effective conjugation length and increases the optical gap. However, this effect is found to dominate strongly in the bis-configurations of the molecules as compared to the nonbis compositions. In order to reduce this effect for rational designing of effective D-A-D type chromophores with less steric hindrance, the role of π-conjugated ethylene (-CH═CH-) linkage/spacer between the A-A units is explored further. Here, it is found that introduction of such linkage substantially decreases the steric hindrance and, thereby, the optical gap as well. Besides this, our study also highlights and explains the impact of the acceptor moiety in improving the absorption capabilities of these molecules in the low-energy region.

The transition-state (TS) region of the simplest heavy-light-heavy type of reaction, F• + H–F → F–H + F•, is investigated in this work by a joint experimental and theoretical approach. Photodetaching the bifluoride anion, [F···H···F]−, generates a negative ion photoelectron (NIPE) spectrum with three partially resolved bands in the electron binding energy (eBE) range of 5.4–7.0 eV. These bands correspond to the transition from the ground state of the anion to the electronic ground state of [F–H–F]• neutral, with associated vibrational excitations. The significant increase of eBE of the bifluoride anion, relative to that of F–, reflects a hydrogen bond energy between F– and HF of ∼46 kcal/mol. Theoretical modeling reveals that the antisymmetric motion of H between the two F atoms, near the TS on the neutral [F–H–F]• surface, dominates the observed three bands, while the F–H–F bending, F–F symmetric stretching modes, and the couplings between them are calculated to account for the breadth of the observed sp...

Quantum and quasiclassical calculations have been performed to compute the low energy efficiency of the Li + ClH → LiCl + H reaction on some potential energy surfaces fitted to ab initio electronic energies using different functional forms. The outcomes of the calculations show marked differences at threshold and in the shape of the excitation function in seeming contrast with the height of the saddle to reaction and the width of the cone of acceptance. The differences in the computed reactive probability and cross section are rationalized in terms of the attractive/repulsive nature of the long-range interaction and the inability of trajectory techniques to deal with threshold effects. The vestiges of these features in the value of the thermal rate coefficients are also commented on.

Ethane core–silver shell clusters consisting of several thousand particles have been assembled in helium droplets upon capture of ethane molecules followed by Ag atoms. The composite clusters were studied via infrared laser spectroscopy in the range of the C–H stretching vibrations of ethane. The spectra reveal a splitting of the vibrational bands, which is ascribed to interaction with Ag. A rigorous analysis of band intensities for a varying number of trapped ethane molecules and Ag atoms indicates that the composite clusters consist of a core of ethane that is covered by relatively small Ag clusters. This metastable structure is stabilized due to fast dissipation in superfluid helium droplets of the cohesion energy of the clusters.

Methyl halides have been used to test basis set effects on simulations of strong field ionization using time dependent configuration interaction with an absorbing potential. Standard atom centered basis sets need to be augmented by several sets of diffuse functions on each atom so that the wave function in the strong field can interact with the absorbing potential used to model ionization. An absorbing basis of 3 s functions, 2 p functions, 3 d functions, and 1 f function is sufficient for CH3F. Large absorbing basis sets with 4 s functions, 3 or 4 p functions, 4 or 5 d functions, and 2 f functions are recommended for the heavier halogens. The simulations used static fields in the 0.035-0.07 au range to explore the angular dependence of ionization of methyl halides. CH3F ionizes mainly from the methyl group; CH3Cl and CH3Br show ionization from both the methyl group and the halogen, and CH3I ionizes almost exclusively from the pπ orbitals of the iodine.