Van Der Waals Complexes Research Articles

DFT Insight into the Kinetics and Mechanism of OH⋅‐Initiated Atmospheric Oxidation of Catechol: Addition of 3∑g− O2 and Isomerization of Peroxy Radicals

AbstractAtmospheric oxidation mechanism of predominant catechol‐OH adduct [C6H6O2−OH]⋅ (AD2) by oxygen molecule in its triplet electronic ground state and isomerization processes of catechol peroxy radicals [C6H6O2−OH]⋅−O2 into bicyclic peroxy radicals have been studied at the M06‐2X/aug‐cc‐pVTZ level in conjugation with the RRKM theory. The first step begins via the complexation of [C6H6O2−OH]⋅ with oxygen molecule and formation of two pre‐reactive van der Waals complexes in syn and anti modes. Syn mode addition of O2 is more favorable over the anti mode due to the formation of intramolecular hydrogen bond. Kinetically and thermodynamically, addition of O2 at the C5 position in syn mode, namely peroxy radical AD2‐5OO‐syn, is the most efficient process with bimolecular RRKM rate coefficient 2.80×10−16 cm3 molecule−1 s−1 at ambient conditions. Isomerization (cyclization) of peroxy radical AD2‐5OO‐syn into bicyclic peroxy radicals via the formation of −OO− bridge are strongly endothermic and nonspontaneous processes with high activation energies. Ring closure into the bicyclic peroxy radical AD2‐5,6OO‐syn is the most favorable process with unimolecular RRKM rate coefficient 1.41×10−8 s−1 at ambient conditions.

Quantum nuclear delocalization and its rovibrational fingerprints.

Quantum mechanics dictates that nuclei must undergo some delocalization.In this work, emergence of quantum nuclear delocalization and its rovibrational fingerprints are discussed for the case of the van der Waals complex HHe3+.The equilibrium structure of HHe3+ is planar and T-shaped,one He atom solvating the quasi-linear He-H+-Hecore.The dynamical structure of HHe3+, in all of its bound states, isfundamentally different.As revealed by spatial distribution functions and nuclear densities, during thevibrations of the molecule the solvating He is not restricted to be in the planedefined by the instantaneously bent HHe3+ chomophore, but freely orbits the central proton, forming a three-dimensional torus around the HHe2+ chromophore.This quantum delocalization is observed for all vibrational states, the type ofvibrational excitation being reflected inthe topology of the nodal surfaces in the nuclear densities,showing, for example, that intramolecular bending involvesexcitation along the circumference of the torus.

Quantum Nuclear Delocalization and its Rovibrational Fingerprints

AbstractQuantum mechanics dictates that nuclei must undergo some delocalization. In this work, emergence of quantum nuclear delocalization and its rovibrational fingerprints are discussed for the case of the van der Waals complex . The equilibrium structure of is planar and T‐shaped, one He atom solvating the quasi‐linear He−H+−He core. The dynamical structure of , in all of its bound states, is fundamentally different. As revealed by spatial distribution functions and nuclear densities, during the vibrations of the molecule the solvating He is not restricted to be in the plane defined by the instantaneously bent chomophore, but freely orbits the central proton, forming a three‐dimensional torus around the chromophore. This quantum delocalization is observed for all vibrational states, the type of vibrational excitation being reflected in the topology of the nodal surfaces in the nuclear densities, showing, for example, that intramolecular bending involves excitation along the circumference of the torus.

Simple Physical Model for the Estimation of Irreversible Dissociation Rates for Bimolecular Complexes.

In this article, we propose a simple method of estimating dissociation rates of bimolecular van der Waals complexes ("wells"), rooted in rigid body dynamics, requiring as input parameters only the bimolecular binding energy, together with the intermolecular equilibrium distance and moments of inertia of the complex. The classical equations of motion are solved for the intermolecular and rotational degrees of freedom in a coordinate system considering only the relative motion of the two molecules, thus bypassing the question of whether the energy of the complex is statistically distributed. Well-escaping trajectories are modeled from these equations, and the escape rate as a function of relative velocity and angular momentum is fitted to an empirical function, which is then integrated over a probability distribution of said quantities. By necessity, this approach makes crude assumptions on the shape of the potential well and neglects the impact of energy quantization, and, more crucially, the coupling between the degrees of freedom included in the equations of motion with those that are not. We quantify the error caused by the first assumption by comparing our model potential with a quantum chemical potential energy surface (PES) and show that while the model does make several compromises and may not be accurate for all classes of bimolecular complexes, it is able to produce physically consistent dissociation rate coefficients within typical atmospheric chemistry confidence intervals for triplet state alkoxyl radical complexes, for which the detailed balance approach has been shown to fail.

Experimental and Theoretical Studies of the HeICl Van der Waals Complexes in the Valence and Ion-pair States.

The article presents results of experimental and theoretical analysis of the T-shaped and linear HeICl van der Waals complexes in the valence A1 and ion-pair β1 states as well as the HeICl(A1,vA ,nA ←X0+ ,vX =0,nx and β1,vβ ,nβ ←A1,vA ,nA ) optical transitions (ni are quantum numbers of the vdW) modes). The HeICl(β1,vβ ,nβ )→He+ICl(E0+ , , β1) decay are also studied. Luminescence spectra of the HeICl(β1,vβ =0-3,nβ ) complex electronic (ICl(E0+ ,vE , ) and vibrational ICl(β1,vβ ) predissociation products are measured, and branching ratios of decay channels are determined. To construct potential energy surfaces for the HeICl(A1, β1) states, we utilized the intermolecular diatomic-in-molecule perturbation theory first order method. Experimental and calculated spectroscopic characteristics of the A1 and β1 states agree well. Comparison of the experimental and calculated pump-probe, action and excitation spectra shows that the calculated spectra describe the experimental spectra adequately.

Understanding the high-resolution spectral signature of the N2-H2O van der Waals complex in the 2OH stretch region.

We present the observation of the N2-H2O van der Waals complex in the 2OH stretch overtone region. The high-resolution jet cooled spectra were measured using a sensitive continuous wave cavity ringdown spectrometer. Several bands were observed and vibrationally assigned in terms of ν1, ν2, and ν3, the vibrational quantum numbers of the isolated H2O molecule, as (ν1'ν2'ν3')←(ν1″ν2″ν3″)=(200)←(000) and (101) ← (000). A combination band involving the excitation of the in-plane bending motion of N2 and the (101) vibration of water is also reported. The spectra were analyzed using a set of four asymmetric top rotors, each associated with a nuclear spin isomer. Several local perturbations of the (101) vibrational state were observed. These perturbations were assigned to the presence of the nearby (200) vibrational state and to the combination of (200) with intermolecular modes.

Rovibrational spectra of SO2-containing van der Waals complexes in the v1 region of SO2. Part II. SO2–H2O and SO2–D2O

Jet-cooled rovibrational absorption spectra of SO2–H2O and SO2–D2O complexes have been measured in the v1 symmetric stretching region of SO2 around 1151 cm−1 using a segmented rapid-scan quantum cascade laser spectrometer. The rovibrational spectrum of SO2–D2O has also been measured in the v2 bending region of D2O around 1178 cm−1. The tunneling splittings caused by the internal rotation of the water unit could not be resolved under our experimental conditions. The observed rovibrational transitions for these two complexes are analyzed using a standard A-reduced Watson asymmetric top Hamiltonian, yielding precise molecular constants for the excited vibrational states. The experimental band-origins are 1156.713866(70) cm−1 for SO2–H2O and 1156.819797(66) cm−1 for SO2–D2O in the v1 region of SO2, and 1180.177901(58) cm−1 for SO2–D2O in the v2 region of D2O.

Investigating the Rydberg states and photodissociation dynamics of Kr2using velocity map imaging

Although the krypton dimer, Kr2, is a prototypical weakly bound van der Waals complex in its ground electronic state, the excited states of Kr2exhibit many and various interactions. Resonance-enhanced multiphoton ionization and velocity map imaging provide an avenue to explore the electronic structure and photofragmentation dynamics of Kr2in the vacuum ultraviolet region. By monitoring photofragmentation product channels and recoil anisotropy distributions, one can gain insights into excited state symmetries and lifetimes, which can aid in interpreting spectroscopy. Here, we study the spectroscopy and photodissociation dynamics of Kr2in the 91 000–94 500 cm−1region. We record and assign photofragment product channels for 32 vibronic bands corresponding to seven electronic transitions. We also identify two previously unobserved vibronic band systems, which we assign as the Kr2 5p [5/2]3 [Formula: see text] and 5p [3/2]2[Formula: see text] transitions. Velocity map images show photofragments arising from predissociation of the neutral Rydberg states and from dissociative photoionization at the n > 2 photon level. We also observe variation in branching ratios between the predissociative and dissociative photoionization channels depending on the lifetime of the intermediate; longer lived states favour higher dissociative photoionization yields and exhibit β6anisotropy parameters for predissociation product channels, indicating “rotational smearing” of the product angular distributions.

Noncovalent chalcogen and tetrel bonding interactions: Spectroscopic study of halide–carbonyl sulfide complexes

AbstractChalcogen and tetrel intermolecular bonding interactions formed between carbonyl sulfide and halide anions have been studied utilizing a combined experimental and theoretical approach. In particular, high‐level CCSD(T) energetics and experimental anion photoelectron spectroscopy have been used in order to assign the dominant binding motif exhibited in these complexes. Halide anions solvated by multiple carbonyl sulfide molecules have also been investigated in order to ascertain the effect that additional binding partners has on the strength of the noncovalent interactions. The experimental and computational results support the main binding motif of carbonyl sulfide molecules with halide anions being chalcogen bonding, both in dimer complexes and larger solvated complexes. In addition, comparison between the noncovalent interactions formed by halides with carbon disulfide, carbonyl sulfide, and carbon dioxide allows a deeper understanding of noncovalent binding strength in relation to isoelectronic species.Key points Spectroscopic and ab initio characterization of halide–carbonyl sulfide van der Waals complexes bound through chalcogen and tetrel bonding. Detailed insight into chalcogen and tetrel bond strength in the context of changing chemical environments. Effect of increasing solvation on noncovalent binding strength.

Electronic structure of PH2− containing complexes as photoelectron spectroscopy candidates

Phosphine is attracting interest due to the role it plays in extraterrestrial and interplanetary atmospheric environments. Phosphorus hydride anion and neutral van der Waals complexes with CH4, C2H4, HCCH, CO2, H2S and NH3 have been investigated as potential targets for photoelectron spectroscopy using a combination of DSD-PBEP86-D3BJ optimised geometries, W2w energies and Franck–Condon simulations. All anion complexes exhibit hydrogen-bonding interactions and while complexes with CH4 are weakly bound, showing minimal perturbation upon complexation. All other solvating molecules studied yield sufficient energetic or vibrational structural differences to be differentiable in photoelectron spectra. Most notably, PH2−⋯CO2 undergoes barrierless nucleophilic addition to form the phosphino formate anion (PH2COO−) and is proposed as one such potential atmospheric sink.

Fine-structure excitation of CCS by He: Potential energy surface and scattering calculations.

The fine structure excitation of the interstellar CCS radical induced by collisions with He is investigated. The first potential energy surface (PES) for the CCS-He van der Waals complex is presented. It was obtained from a highly correlated spin unrestricted coupled cluster approach with single double and perturbative triple excitations. The PES presents two shallow minima of 31.85 and 37.12 cm-1 for the linear (He facing S) and the nearly T-shaped geometries, respectively. The dissociation energy of the complex was calculated and found to be D0 = 14.183 cm-1. Inelastic scattering calculations were performed using the close-coupling approach. Cross-sections for transitions between the 61 first fine structure levels of CCS were obtained for energy up to 600 cm-1 and rate coefficients for the 5-50K temperature range were derived. This set of collisional data can be used to model CCS emission spectra in dark molecular interstellar clouds and circumstellar envelopes and enable an accurate determination of CCS abundance in these astrophysical media.

Machine learning identification of atmospheric gases by mapping the graphene-molecule van der waals complex bonding evolution

Atmospheric doping of graphene, and the variation in atmospheric composition (e.g., humidity) makes graphene machine learning (ML) models limited to controlled environments (e.g., dry air), and unsuitable for atmospheric applications (e.g., non-invasive medical diagnosis). Herein, using nano-porous activated carbon for atmospheric passivation of the graphene channel, Extreme Gradient Boosting (XGBoost), K-nearest neighbors (KNN), and Naïve Bayes supervised ML models for atmospheric gas identification were developed, with model feature contribution studied using the Game theoretic approach, SHapley Additive exPlanations (SHAP). Unlike conventional graphene-based ML models which only monitor the gas adsorption induced doping and scattering without tuning voltage (Vt) modulation, in this work, the tuning voltage evolution of the gas adsorption induced van der Waals (vdW) complex doping and scattering characteristics was mapped out over time. The accuracy, precision, recall, and F1-score of the developed models in the environments: atmospheric ammonia, atmospheric acetone, ammonia in dry air, and acetone in nitrogen were 100% for XGBoost, 96%, 97%, 97%, 97% respectively for KNN, and 95%, 95%, 96%, 96% respectively for Naïve Bayes, even at single-digit ppb gas concentrations. Hence, our results advance the application of graphene based electronic nose models from conventional controlled environments to actual atmospheric sensing.

Calculation of the Transport and Relaxation Properties of the Ar···HCl van der Waals Complex Using a New Potential Energy Surface: Comparison of the Classical and Full Quantum Mechanical Kinetic Theory Results with Molecular Dynamics Simulations.

The intermolecular potential energy surface (PES) of the Ar···HCl complex was calculated at the RCCSD(T)/aug-cc-pvQz-BF level of theory. The obtained potential was expanded in terms of Legendre polynomials and fitted to a mathematical model. The fitting results are highly correlated with the ab initio PES data with SD = 5.9 × 10-3 cm-1 and average absolute deviation (AAD) = 4.0 × 10-6 cm-1. The interaction second virial coefficients (B12) in the temperature range of 190-480 K were calculated by considering classical and first quantum corrections and compared with the available experimental data. A reasonable agreement with the experimental and calculated B12 was obtained. The PES was also used to obtain the rovibrational energy levels, and the spectroscopic rovibrational constants were obtained. It was found that the D0 values differ ∼2.25 cm-1 from the experimental values of the ground rovibrational state. Furthermore, the obtained potential was used to calculate the transport and relaxation properties using full quantum close-coupling (CC) formalism and the classical kinetic theory methods based on the Mason-Monchik approximation (MMA). It was found that the deviation between MMA and CC calculations is increased with increasing the temperature due to the higher influence of the rotational degrees of freedom on the transport properties. Also, the contribution of the inelastic (off-diagonal) transitions for diffusion coefficient is higher than the viscosity. Furthermore, the classical molecular dynamics simulations were performed using LJ(12,6) and Vashishta models, to calculate the interaction diffusion and viscosity coefficients, and compared with the results of the full quantum CC calculations. The obtained results confirm that the Vashishta model is better fitted to the ab initio potentials and is more accurate than LJ(12,6) in calculation of the diffusion coefficients.

Neural network method for constructing intermolecular potential energy surfaces of van der Waals complexes

This study proposes a new approach for constructing intermolecular potential energy surfaces (PESs) of van der Waals (vdW) complexes using neural networks. The descriptors utilized in this neural network model are split into two parts: radial parts representing the intermolecular stretching vibrations between monomers and angular parts describing the relative orientation of these molecules. Specifically, the parity-adapted rotational basis functions used in the bound state calculation are taken as the angular descriptors, which ensure the correct symmetry of the PES. The number of orthogonal rotational basis functions is controlled by the maximum value of the angular momentum quantum number. In addition, the symmetry of monomer molecules is achieved by restricting the quantum number of the rotational basis function. The descriptors for five types of van der Waals complexes, including atom-linear, atom-nonlinear, linear-linear, linear-nonlinear and nonlinear-nonlinear molecules complexes, have been derived in this work. The neural network models with these newly developed descriptors were then applied to construct PESs of two van der Waals complexes, Ar-NaCl and N2-OCS. The root-mean-square error values between the fitted and ab initio energies are found to be 0.11 cm−1 and 0.26 cm−1 for Ar-NaCl and N2-OCS, respectively. These results indicate that this method is accurate and effective for constructing high-precision PESs of vdW complexes.

Quantum mechanical and classical calculation of the transport and relaxation properties of He⋯CO2 complex using a new PES.

The intermolecular potential energy surface (PES) of He⋯CO2 van der Waals (vdW) complex was computed at the RCCSD(T)/aug-cc-pvQz-BF level of theory. The obtained potential was fitted to an exact mathematical model using the Legendre expansion method. The fitted PES model was then used to calculate the interaction second virial coefficients (B12) considering the classical and first quantum corrections, and compared with the available experimental data in the temperature range of T = 50-463.2 K. The results of the experimental and calculated B12 reasonably agree. The fitted potential was also applied to compute the transport and relaxation properties of He⋯CO2 complex from classical Mason-Monchick approximation (MMA) and Boltzmann weighting method (BWM), and the full quantum mechanical close-coupling (CC) solution of the Waldmann-Snider kinetic equation. The average absolute deviation percent (AAD%) of the experimental and CC calculated viscosity (η12) and diffusion coefficients (D12) were found to be 1.4% and 1.9%, respectively, which are in the range of the experimental uncertainties. However, the AAD% of MMA for η12 and D12 were found to be 11.2% and 11.9%, respectively. It was also found that as the temperature increased, the accuracy of MMA decreased compared to the CC method, which may be related to the elimination of the contribution of the rotational degrees of freedom, especially the off-diagonal elements in the classical MMA method. Furthermore, equilibrium classical molecular dynamics (MD) simulations based on the Green-Kubo time correlation function were performed using the Morse, LJ(12,6), and Vashishta potential models to calculate η12 and D12. The AAD% for η12 and D12 were found to be ∼13% and ∼30%, respectively, at the temperature range of T = 200-1000 K.

Towards the generation of potential energy surfaces of weakly bound medium-sized molecular systems: the case of benzonitrile-He complex.

Currently, the explicitly correlated coupled cluster method is used routinely to generate the multi-dimensional potential energy surfaces (mD-PESs) of van der Waals complexes of small molecular systems relevant for atmospheric, astrophysical and industrial applications. Although very accurate, this method is computationally prohibitive for medium and large molecules containing clusters. For instance, the recent detections of complex organic molecules (COMs) in the interstellar medium, such as benzonitrile, revealed the need to establish an accurate enough electronic structure approach to map the mD-PESs of these species interacting with the surrounding gases. As a benchmark, we have treated the case of the polar molecule benzonitrile interacting with helium, where we use post-Hartree-Fock and symmetry-adapted perturbation theory (SAPT) techniques. Accordingly, we show that MP2 and distinguishable-cluster approximation (DCSD) cannot be used for this purpose, whereas accurate enough PESs may be obtained using the corresponding explicitly correlated versions (MP2-F12 or DCSD-F12) with a reduction in computational costs. Alternatively, computations revealed that SAPT(DFT) is as performant as CCSD(T)-F12/aug-cc-pVTZ, making it the method of choice for mapping the mD-PESs of COMs containing clusters. Therefore, we have used this approach to generate the 3D-PES of the benzonitrile-He complex along the intermonomer Jacobi coordinates. As an application, we have incorporated the analytic form of this PES into quantum dynamical computations to determine the cross sections of the rotational (de-)excitation of benzonitrile colliding with helium at a collision energy of 10 cm-1.

New rovibrational subbands of Ar-D<sub>2</sub>O complex in the D<sub>2</sub>O bending mode region

The intermolecular interactions involving the water molecule play important roles in many fields of physics, chemistry, and biology. High-resolution spectroscopy of Van der Waals complexes formed by a rare gas atom and a water molecule can provide a wealth of information about these intermolecular interactions. The precise experimental data can be used to test the accuracies and efficiencies of various theoretical methods of constructing the intermolecular potential energy surfaces and calculating the bound states. In this work, the high-resolution infrared absorption spectrum of the Ar-D<sub>2</sub>O complex in the <i>v</i><sub>2</sub> bending region of D<sub>2</sub>O is measured by using an external cavity quantum cascade laser. A segmented rapid-scan data acquisition method is employed. The Ar-D<sub>2</sub>O complex is generated in a slit supersonic jet expansion by passing Ar gas through a vessel containing liquid D<sub>2</sub>O. Four new rovibrational subbands are assigned in the spectral range of 1150–1190 cm<sup>–1</sup>, namely <inline-formula><tex-math id="M1">\begin{document}$\Sigma \left( {{0_{00}}, {v_2} = 1} \right) \leftarrow \Sigma \left( {{1_{11}}} \right)$\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="1-20221728_M1.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="1-20221728_M1.png"/></alternatives></inline-formula>, <inline-formula><tex-math id="M2">\begin{document}$\Sigma \left( {{0_{00}}, {v_2} = 1} \right) \leftarrow \Pi \left( {{1_{11}}} \right)$\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="1-20221728_M2.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="1-20221728_M2.png"/></alternatives></inline-formula>, <inline-formula><tex-math id="M3">\begin{document}$\Sigma \left( {{1_{01}}, {v_2} = 1} \right) \leftarrow \Pi \left( {{1_{10}}} \right)$\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="1-20221728_M3.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="1-20221728_M3.png"/></alternatives></inline-formula> and <inline-formula><tex-math id="M4">\begin{document}$\Sigma \left( {{1_{01}}, {v_2} = 1} \right) $\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="1-20221728_M4.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="1-20221728_M4.png"/></alternatives></inline-formula><inline-formula><tex-math id="Z-20221230153751">\begin{document}$\leftarrow \Pi \left( {{1_{01}}} \right) $\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="1-20221728_Z-20221230153751.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="1-20221728_Z-20221230153751.png"/></alternatives></inline-formula>. The first two subbands belong to the <i>otho</i>- species of Ar-D<sub>2</sub>O, while the latter two belong to the <i>para</i>- species. The observed rovibrational transitions together with the previously reported pure rotational spectra having the common lower vibrational sub-states are analyzed by a weighted least-squares fitting using a pseudo-diatomic effective Hamiltonian. An experimental error of 10 kHz for the far-infrared transitions and 0.001 cm<sup>–1</sup> for the infrared transitions are set in the global fitting when using Pickett’s program SPFIT, respectively. The molecular constants including vibrational substate energy, rotational and centrifugal distortion constants, and Coriolis coupling constant, are determined accurately. The previous results for the <inline-formula><tex-math id="M5">\begin{document}$\Pi \left( {{1_{11}}, {v_2} = 0} \right)$\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="1-20221728_M5.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="1-20221728_M5.png"/></alternatives></inline-formula> substate are found to be likely incorrect. The energy of the <inline-formula><tex-math id="M6">\begin{document}$\Sigma \left( {{0_{00}}, {v_2} = 1} \right)$\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="1-20221728_M6.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="1-20221728_M6.png"/></alternatives></inline-formula>and <inline-formula><tex-math id="M7">\begin{document}$\Sigma \left( {{1_{01}}, {v_2} = 1} \right)$\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="1-20221728_M7.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="1-20221728_M7.png"/></alternatives></inline-formula>substates are determined experimentally for the first time. The band origin of Ar-D<sub>2</sub>O in the D<sub>2</sub>O <i>v</i><sub>2</sub> bending mode region is determined to be 1177.92144(13) cm<sup>–1</sup>, which is a red shift about 0.458 cm<sup>–1</sup> compared with the head of D<sub>2</sub>O monomer. The experimental vibrational substate energy is compared with its theoretical value based on a four-dimensional intermolecular potential energy surface which includes the normal coordinate of the D<sub>2</sub>O <i>v</i><sub>2</sub> bending mode. The experimental and theoretical results are in good agreement with each other. But the calculated energy levels are generally higher than the experimental values, so, there is still much room for improving the theoretical calculations.

Rotational spectra and semi-experimental structures of furonitrile and its water cluster.

Rotational spectroscopy represents an invaluable tool for several applications: from the identification of new molecules in interstellar objects to the characterization of van der Waals complexes, but also for the determination of very accurate molecular structures and for conformational analyses. In this work, we used high-resolution rotational spectroscopic techniques in combination with high-level quantum-chemical calculations to address all these aspects for two isomers of cyanofuran, namely 2-furonitrile and 3-furonitrile. In particular, we have recorded and analyzed the rotational spectra of both of them from 6 to 320 GHz; rotational transitions belonging to several singly-substituted isotopologues have been identified as well. The rotational constants derived in this way have been used in conjunction with computed rotation-vibration interaction constants in order to derive a semi-experimental equilibrium structure for both isomers. Moreover, we observed the rotational spectra of four different intermolecular adducts formed by furonitrile and water, whose identification has been supported by a conformational analysis and a theoretical spectroscopic characterization. A semi-experimental determination of the intermolecular parameters has been achieved for all of them and the results have been compared with those obtained for the analogous system formed by benzonitrile and water.

Temperature‐dependent kinetics of the reactions of CH2OO with acetone, biacetyl, and acetylacetone

AbstractTemperature‐dependent rate constants for the reactions of CH2OO with acetone (Ac), biacetyl (BiAc), and acetylacetone (AcAc) have been measured over the range 275–335 K using a flash photolysis, transient absorption spectroscopy technique. The measurements were performed at a total pressure of ∼80 Torr in N2 bath gas, which corresponds to the high‐pressure limit for these reactions. All three reactions show linear Arrhenius plots with negative temperature dependences. Rate constants increase in the order Ac < AcAc « BiAc across the temperature range; at 295 K the rate constants are kAc = (4.8 ± 0.4) × 10–13 cm3 s–1, kAcAc = (8.0 ± 0.7) × 10–13 cm3 s–1, and kBiAc = (1.10 ± 0.09) × 10–11 cm3 s–1. Sensitivity to temperature, characterized by the magnitude of the negative activation energy, increases in the order AcAc < BiAc < Ac (Ea/R values of –1830 ± 170 K, –1260 ± 170 K, and –460 ± 180 K, respectively). CBS‐QB3 calculations show that the Ac and BiAc reactions proceed via formation of an entrance channel complex followed by 1,3‐dipolar cycloaddition to form secondary ozonide products via a submerged transition state. For the BiAc reaction, the rate limiting step appears to be rearrangement of a long‐range van der Waals complex into the short‐range complex that subsequently leads directly to the cycloaddition transition state with a very low energy barrier. The calculations show that two reaction pathways are competitive for AcAc with nearly identical transition state free energies (ΔG° = +10.1 kcal mol–1 at 298 K) found for cycloaddition at the C=O and at the C=C site of the dominant enolone tautomer. The weak temperature dependence observed is likely due to competition between these pathways.

γ-graphyne: A promising electron acceptor for organic photovoltaics

The search for new materials is constantly ongoing. Recently, a two-dimensional carbon allotrope , γ-graphyne, has been synthesized with a unified crystalline structure . Because of its low LUMO and excellent electron mobility, it appears to be a promising electron acceptor for photovoltaic applications. Here we report an analysis of the electronic properties of model van der Waals complexes of γ-graphyne with several partners of different electronic nature. We show that photoinduced electron transfer from electron-donating partners to γ-graphyne is favorable and occurs on nano to picosecond time scale. In contrast, electron transfer from γ-graphyne to strong electron acceptors is unlikely. Our results open perspectives for the future application of γ-graphyne in photovoltaic devices.