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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]

The trigonal prismatic MnO 6 is a basic structural unit of Mn-based compound which has been seldom explored in theoretical and experimental studies. In this paper, the diffusion potential energy surfaces of Li+, Na+, K+, Mg2+, Al3+, and NH 4 + ion in trigonal prismatic 1H-MnO 2 are presented, which give an intuitionistic picture of the Jahn-Teller effect on the diffusion process. Based on the nudged elastic band method, it is found that the diffusion of ions in trigonal prismatic MnO 2 is accompanied by consecutive structural distortion. The low diffusion barriers indicate trigonal prismatic MnO 2 is a fast ion conductor. Band structure calculations show the semimetal characteristic of the intercalated compound, which is fit for high electrochemical performance. The details of the diffusion process are also highlighted. Our theoretical study provides an in-depth understanding and research on the fundamentals of the diffusion process in the special configuration in MnO 2 and helps to develop novel high-performance electrodes. [ABSTRACT FROM AUTHOR]

• 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]

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]

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]

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]

CHN 7 and CN 7 − are meta-stable species. In order to study on the relationship between thermodynamic and kinetic stabilities, the potential energy surfaces of CHN 7 and CN 7 − were scanned at the B3LYP/aug-cc-pVDZ level. After the analysis of potential energy surfaces, the optimum pathways were got to conclude the dissociation and formation mechanisms. The dissociation barriers of 5-azido-1 H -tetrazole and 5-azido-2 H -tetrazole are about 150 kJ mol −1 . They are sufficient to keep the two azidotetrazoles stable. The reaction between cyanogen azide and azide anion cannot produce azidotetrazolate anion, but produce the linear CN 7 − with a lower barrier. The reaction between cyanogen azide and hydrazoic acid preferentially produce 5-azido-1 H -tetrazole. The decyclization barriers of 1 H -tetrazolo[1,5- d ]tetrazole and tetrazolo[1,5- d ]tetrazolate anion are 44.7 and 81.6 kJ mol −1 , respectively. The deprotoned anion is more available than the neutral compound. Heptaazacubane and heptaazacubanide anion with cubic geometries are highly unstable. [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]

We study the benzene-Rn (BzRn) complex in its electronic ground state using an ab initio scalar relativistic method in the framework of the coupled-cluster level of theory with single, double, and perturbative triple excitations [CCSD(T)]. Two different approaches to treat the scalar relativistic effects have been tested — the small-core pseudopotential (PP) and the Douglas–Kroll–Hess (DKH) Hamiltonian. These methods were used with the augmented Dunning's double zeta basis set for C and H atoms, and the augmented triple PP basis set for Rn supplemented by midbond functions. Additionally, the effects of the basis extension for C and H atoms and the extension of the correlation space to include the internal orbitals of Rn and C have been tested. The comparison of the binding energy D e and the equilibrium coordinate z e found with different methods has allowed to choose the optimal one based on PP for the construction of the analytical potential energy surface (PES). The long-range part of the potential has been fitted separately and the obtained long-range coefficients have been compared to their counterparts calculated from the first principles using the CCSD polarization propagator. The vibrational energy level pattern of BzRn has been studied, and the revealed polyad structure of the complex has been compared to the previously studied benzene-Kr and benzene-Xe complexes. A Python code that yields the interaction energy at any Rn position is provided. [ABSTRACT FROM AUTHOR]

Quantum mechanical close coupling calculation of the state-to-state transport and relaxation cross sections have been done for Hg-H 2 molecular system using a high-level ab initio potential energy surface. Rotationally averaged cross sections were also calculated to obtain the energy dependent Senftleben-Beenakker cross sections at the energy range of 0.005–25,000 cm −1 . Boltzmann averaging of the energy dependent Senftleben-Beenakker cross sections showed the temperature dependency over a wide temperature range of 50–2500 K. Interaction viscosity and diffusion coefficients were also calculated using close coupling cross sections and full classical Mason-Monchick approximation. The results were compared with each other and with the available experimental data. It was found that Mason-Monchick approximation for viscosity is more reliable than diffusion coefficient. Furthermore, from the comparison of the experimental diffusion coefficients with the result of the close coupling and Mason-Monchick approximation, it was found that the Hg-H 2 potential energy surface used in this work can reliably predict diffusion coefficient data. [ABSTRACT FROM AUTHOR]

Three dimensional ab initio potential energy surfaces (PESs) have been computed for the ground state and low-lying excited states of HCS + molecular ion using the internally contracted multi-reference (single and double) configuration interaction and augmented correlation consistent polarized valence quadruple zeta (aug-cc-pVQZ) basis sets. Ground state global PES is analyzed as dissociation of molecular ion into H + CS + . The ground state PES (H + CS + ) has been fitted by the inverse power series expansion function. The anisotropy of the surface has been analyzed in terms of the multipolar expansion coefficients for the rigid-rotor surface. The surface will be useful for detailed understanding of collision dynamics in terms of ro-vibrational cross sections and rate coefficients. [ABSTRACT FROM AUTHOR]

The cyclooctatetraene (COT) anion has a stable D 4h structure that is similar to the transition state configurations of the neutral C–C bond-alternation ( D 4h ↔ D 8h ↔ D 4h ) and ring-inversion ( D 2d ↔ D 4h ↔ D 2d ) unimolecular reactions. The previously measured photodetachment spectrum of COT − revealed the reaction dynamics in the vicinity of the two transition states on the neutral potential energy surface. In this work, the photodetachment spectrum is calculated quantum mechanically on ab initio -level potential energy surfaces within a three degree-of-freedom reduced-dimensionality model. Very good agreement has been obtained between theory and experiment, providing reliable interpretations for the experimental spectrum. A detailed picture of the reactive molecular dynamics of the COT unimolecular reaction in the transition state region is also discussed. [ABSTRACT FROM AUTHOR]

Five-dimensional morphed potentials have been generated for the prototype hydrogen-bonded H 2 O-HF and halogen-bonded H 2 O-F 2. These determined morphed potentials formed the basis for modeling the dynamics of the complexes and predicting accurate intermolecular rovibrational frequencies. The discrepancy between previous experimental and ab initio predictions for the dissociation energy of the H 2 O-HF complex is discussed. Predictions based on the morphed potential and application of the Badger-Bauer rule give better estimates for the dissociation energy of the H 2 O-HF complex, that are in better agreement with the experimental prediction. It is found that the H 2 O-HF and H 2 O-F 2 complexes have similar equilibrium and ground state geometries. This is in agreement with recent developed canonical approaches to potential energy surfaces, which demonstrated that there are no fundamental distinctions between hydrogen and halogen bonds. [ABSTRACT FROM AUTHOR]

A new global potential energy surface of the ground state of the RbH 2 system is constructed by using the permutation invariant polynomial neural network method. In the ab initio calculations, the aug-cc-pVQZ basis set for H, Def2-QZVPP basis set for Rb, and multi-reference configuration interaction method with Davidson correction are used. The topographical features of the new PES are discussed in detail, and no wells and barriers in the minimum energy path are found. Thereafter, specific initial-state dynamics calculations of the H + RbH (v = 0 ∼ 2, j = 0) → Rb + H 2 reaction are carried out based on the new PES by means of the time-dependent quantum wave packet method with a second-order split operator. The dynamics results indicate that the vibrational excitation of RbH molecules reduces and increases the reaction probability when the collision energy is below 0.4 eV and above 0.4 eV, respectively. [ABSTRACT FROM AUTHOR]

The intermolecular potential energy surface (PES) of the ground electronic state for the Ar–BrCl dimer is constructed at the CCSD(T) level with the aug-cc-pVQZ basis set and mid-bond functions. The PES is characterized by three minima and two saddle points. The global minimum corresponding to a collinear Ar–BrCl configuration, which has been observed experimentally, is located at R = 4.10 Å and θ = 2.5° with a well depth of −285.207 cm −1 . A nearly T-shaped structure and an anti-linear Ar–ClBr geometry is also predicted. The bound state calculations are preformed to study intermolecular vibrational modes, rotational levels and average structures for the complex. Our transition frequencies, spectroscopic constants and average structures for all isotopomers of the collinear isomer agree well with experimental data. We have also provided pure rotational transitional frequencies for both nearly T-shaped and anti-linear isomers. These results are significant for further experimental investigations of the Ar–BrCl dimer. [ABSTRACT FROM AUTHOR]

A hybrid fitting scheme is proposed for the construction of global analytic ab initio potential energy surfaces (PESs) by means of applying reproducing kernel Hilbert space (RKHS) interpolation and cubic spline interpolation onto different dimensions of the molecular configuration space. In addition to inheriting most advantages of the pure RKHS method, this scheme offers the following extra benefits: short initiation time and enhanced stability and accuracy. We also propose a fast algorithm for the scheme allowing the PES computation time to be independent of the number of ab initio points. We have constructed an adiabatic PES of N( 2 D) + H 2 →NH + H reactive system from more than twenty thousand ab initio points using this scheme. The accurate quantum dynamics results calculated on the constructed PES demonstrate high accuracy and efficiency of this new scheme. [ABSTRACT FROM AUTHOR]

Quantum dynamics for the reaction between S( 3 P ) and NH(X 3 Σ) has been investigated on the lowest three adiabatic 1 A′, 1 A″, and 3 A″ potential energy surfaces, which have been recently developed on the basis of accurate ab initio electronic structure calculations. We employed both time-dependent and time-independent quantum reactive scattering methods. We report collision energy dependence of reactive cross sections and product NS vibrational distributions calculated within adiabatic treatment. The reaction proceeds with a complex-forming mechanism via an initial barrier-less process; however, the results of quantum reactive scattering calculations suggest non-statistical behaviors. The contribution of the HNS/HSN isomerization as well as singlet–triplet spin-forbidden process on the overall reactivity is also discussed. [ABSTRACT FROM AUTHOR]

The lowest three adiabatic potential energy surfaces (1¹ A′, 1¹ A″ and 1³A″) of the HNS molecular system have been developed using ab initio MRCI+Q-level electronic structure calculations with a complete-basis-set approach in order to understand the NS production mechanisms from the S(³P)+NH(X³Σ)→NS(X²Π)+H(²S) and N(4S)+SH(X²Π)→NS(X²Π)+H(²S) reactions. The results of time-independent quantum reactive scattering calculations show that the reactions proceed with the contribution of both direct and HNS/HSN complex-forming mechanisms on all the three potential energy surfaces. It is found that the reaction dynamics is not entirely statistical and cannot be described with a simple capture theory despite that the reactions are barrierless with large exoergicity. [ABSTRACT FROM AUTHOR]

Highlights: [•] B2S can adopt either the B-B-S (singlet) or B-S-B (triplet) conformation. [•] A neural network potential energy surface for B2S transformation is developed. [•] The transformation pathway is predicted using the nudged elastic band method. [•] Molecular dynamics of the transformation is investigated with various excitations. [Copyright &y& Elsevier]

Highlights: [•] High level quantum chemical calculations are performed for two SN2 reactions. [•] The calculated gradient reaction pathways for reactions have an unusual behavior. [•] An unusual saddle point of index two lies on the gradient reaction path. [•] VRI points have been detected by using Newton trajectories for the reaction path. [•] An infinite flow of gradient lines emanates at three equivalent product minima. [ABSTRACT FROM AUTHOR]

Abstract: Nitrate radical (NO3) is reported to be one of the initial decomposition products of RDX, while it has never been detected in experiment studies. This study for the first time theoretically investigated the reactions of H X CN (X =1,2) with NO3 by computational chemistry methods. The calculated results demonstrate that the barrier height of H abstraction reaction of H2CN with NO3 is close to 0kcalmol−1, implying that the reaction may be responsible for the disappearance of NO3 during the decomposition process of RDX. The study encourages further experimental investigation in future. [Copyright &y& Elsevier]

Abstract: Based on the ground state HN2(12A′) potential energy surface (PES), the effects of collision energy and the rotational excitation of the reagent on the product alignment and the orientation for the title reaction are investigated by using quasi-classical trajectory (QCT) method. The distribution of polar angle P(θ r ) at collision energies 2–40kcal/mol with v = 0 and j = 0 level has been presented. The three angle distribution functions P(θ r ), P(), P(θ r , ) and four generalized polarization dependent differential cross sections (PDDCSs) at collision energy of 10kcal/mol with different rotational excitation are plotted. The results show that the product rotational angular momentum j′ is not only aligned, but also oriented along the direction perpendicular to the scattering plane. It has been found that the three angle distributions are sensitive to initially rotational excitation. The HHL mass combination and the property of the PES are used to explain the found results. [Copyright &y& Elsevier]

Abstract: A coupled cluster singles, doubles, and a hybrid treatment of triples [denoted as CCSD(T)-h] has been applied to investigate the equilibrium geometries and harmonic frequencies of five diatomic open-shell molecules, bond breaking potential energy surfaces in C2 and , and the twisting potential energy surface of ethylene. In the present work, CCSD(T)-h calculations are based on the restricted or restricted open-shell Hartree–Fock (RHF or ROHF) reference. A general procedure for constructing the active RHF or ROHF orbitals is proposed. A comparison of CCSD(T)-h with other CC methods show that for all systems CCSD(T)-h is an excellent approximation to CCSDT, being much better than CCSD(T) especially when a molecule exhibits strong multireference character. [Copyright &y& Elsevier]

Abstract: We consider the recursive single commutator (RSC) approximation of the Baker–Campbell–Hausdorff expansion introduced by Yanai and Chan [T. Yanai, G.K.-L. Chan, J. Chem. Phys. 124 (2006) 194106] and apply it in order to approximate the similarity transformation of the Hamiltonian in both traditional and unitary coupled cluster theory. The equilibrium bond distance, harmonic vibrational frequency, and anharmonic constant of H2, HF, N2, CuH, and Cu2 were computed using the coupled cluster approach with single and double excitations (CCSD) and CCSD with the RSC approximation of the similarity-transformed Hamiltonian (CCSD-RSC). Our results demonstrate that the RSC approximation introduces substantial errors in the estimates of molecular properties. The leading pejorative effects of the RSC approximation can be traced back to the imbalanced description of diagrams arising from the term . Following this analysis we consider a modified RSC scheme correct to fourth-order in the energy, which is found to reproduce CCSD results more closely. The RSC scheme is also applied in conjunction with the state-specific multireference coupled cluster approach of Mukherjee and co-workers [U.S. Mahapatra, B. Datta, D. Mukherjee, J. Chem. Phys. 110 (1999) 6171] to compute the potential energy curve of the BeH2 model, the vibrational frequencies of ozone, and the singlet–triplet splitting of p-benzyne. These examples show that the deterioration of the results caused by the RSC scheme is analogous to the one observed in the single-reference case. Implications for the formulation of approximate internally contracted multireference theories are discussed. [Copyright &y& Elsevier]

Abstract: Intermolecular interactions and parameters for use in MD studies of large molecule systems have earlier been determined for hydrocarbons, carbon tetrahalides and sulfur. The paper reports a model representing nonbonding interactions between silane molecules, which were examined in the same way as hydrocarbons in an earlier (neopentane, isopropane, propane, and ethane) study. Intermolecular potentials were determined for 11 combinations of silane compound pairs (silane SiH4, disilane Si2H6, trisilane Si3H8, isotetrasilane Si4H10 and neopentasilane Si5H12) with MP2/aug(df)-6-311G∗ ab initio calculations. The most stable dimer configurations were identified. With use of the modified Morse potential model to represent the interactions, 276 new potential energy surfaces were generated for silane dimers. Separate and generic pair potentials were calculated for the silanes. The pair potentials can be used in MD studies of silanes. [Copyright &y& Elsevier]

Abstract: A multi-coordinate expansion of potential energy surfaces has been used to perform quantum dynamical calculations for reactions showing double-minimum potentials. Starting from the transition state, a fully automated algorithm for exploring the multi-dimensional potential energy surface represented by arbitrary internal or normal coordinates allows for an accurate description of the relevant regions for vibrational dynamics calculations. An interface to our multi-purpose quantum-dynamics program MrPropa enables routine calculations for simple chemical reactions. Illustrative calculations involving potential energy surfaces obtained from explicitly-correlated coupled-cluster calculations, CCSD(T)-F12a, are provided for the tunneling splittings in the isotopologues of hydrogen peroxide and for reaction dynamics based on the enantiomeric inversion of PHDCl. [Copyright &y& Elsevier]

Abstract: Explicitly correlated coupled cluster theory at the (U)CCSD(T∗)-F12a level has been employed to study the vibrational structure of the first two bands of the low-temperature photoelectron spectra of four different isotopomers of the propargyl radical with C2v symmetry (H2C3H, H2C3D, D2C3H, and D2C3D). A five-dimensional anharmonic model is employed to calculate the peak positions and relative intensities. While the first band of the PE spectra of all four isotopomers is dominated by the adiabatic peak, the second band shows a progression in the pseudoantisymmetric CC stretching vibration v 3 with relative intensities of 100:68:23:5:1 for n =0–4 in the case of the most abundant isotopomer. [ABSTRACT FROM AUTHOR]

Abstract: Spin-polarized density functional theory calculation is employed to study the adsorption and dissociation of NO2 molecule on Cu(111) surface. It is shown that the most favorable adsorption structure is the NO2 (T,T-O-,O′-nitrito) configuration which has an adsorption energy of −1.49eV. The barriers for step-wise NO2 dissociation reaction, NO2(g) →N(a) +2O(a), are 1.05 (for O–N–O bond activation), and 2.08eV (for N–O bond activation), respectively, and the entire process is 0.6eV exothermic. The energetics of single N–O dissociation with and without the presence of N atom or O atom on the surface are also calculated. The results indicate that in the presence of O atom on Cu(111) surface would raise the N–O dissociation barrier, whereas in the presence of N atom decrease it. The interaction nature between adsorbates and substrate is analyzed by the local density of states (LDOS) calculation. [ABSTRACT FROM AUTHOR]

Abstract: An extension of the periodic London–Eyring–Polanyi–Sato (PLEPS) function has been recently proposed in order to accurately describe the six-dimensional potential energy surface for two atoms interacting with a periodic rigid surface. However, only the main features were presented so that the present paper aims at precisely describing the necessary details to achieve the fitting procedure of the so-called flexible periodic LEPS function (FPLEPS) to a set of ab initio electronic structure calculations. The topology of the resulting global potential energy surface is compared to that of previously developed models, including a state-of-the-art ab initio potential, for N2 interacting with W(100). The dynamics of dissociative adsorption using these different models is analyzed. [Copyright &y& Elsevier]

Abstract: Calculations of the dynamics of the reactions O(1 D)+H2 →OH+H, O(1 D)+HD→OH+D, O(1 D)+HD→OD+H and O(1 D)+D2 →OD+D have been performed using the quasi-classical trajectory (QCT) method with symplectic integration. The theoretical calculations were carried out on the ground state 1A′ potential energy surfaces (PES) by Dobbyn and Knowles. The distributions of the dihedral angle P(), the angle between k and j′, P(θr ), and the product vibrational state are presented. The results show that the intermediate geometrical structures and lifetimes of the reactive collisions play a vital role in these reactions. [Copyright &y& Elsevier]

Abstract: The chemical mechanism of the 1PN formation was successfully studied by using the CCSD(T)/6-311++G(3df,3pd) level of theory. The 1NH3 + 3PH and 4P+NH3 reaction paths are not energetically favorable to form the 1PN molecule. However, the 3NH+ 3PH, 4N+ 3PH3, 4N+ 3PH, 4P+ 3NH, and 4P+ 2NH2 reaction paths to form the 1PN molecule are only energetically favorable by taking place through specific transition states to form the 1PN molecule. The NH3 + 3PH, 4N+ 1PH3, NH3 + 4P, and 4N+ 2PH2 reactions are spin-forbidden and the probability of hopping for these reactions was estimated to be 0 by the Landau–Zener theory. This is the first detailed study on the chemical mechanism for the 1PN formation. [Copyright &y& Elsevier]

Abstract: The potential energy surfaces for the electronic ground state of the HXeO molecule is constructed from more than 3500 ab initio points at the internally contracted multi-reference configuration interaction with the Davidson correction (icMRCI+Q) level employing large basis sets. The stabilities and dissociation barriers are identified from the potential energy surfaces. The three-body dissociation channel is found to be the dominate dissociation channel for HXeO. Low-lying vibrational energy levels of both HXeO and DXeO are calculated on the three-dimensional potential energy surface using the Lanczos algorithm, and found to be in good agreement with known experimental band origins. [Copyright &y& Elsevier]

Abstract: The reaction of atomic radical N (4S) with NO2 was explored theoretically using density functional, coupled cluster, and Møller–Plesset perturbation theory. The triplet electronic state potential energy surface (PES) was calculated at the G3B3 and CCSD(T)/cc-pVTZ//B3LYP/6-311+G(d,p) levels of theory. Various possible reaction pathways, including the N-adduct-O-shift and four-center ring formation-decomposition reactions, are considered. On the PES of the title reaction, it is shown that the most favorable pathway should be the atomic radical N attacking the N-atom of NO2 firstly to form the adduct 1 NN(OO), followed by one of the NO bonds breaking to give intermediate 2 NNOO, and then leading to the major products P2 (O2 +N2). As efficient routes to the reduction of NO2 to form N2 and O2 are sought, both kinetic and thermodynamic considerations support the viability of this channel. The transition states involved in the generation of products P1 (2NO), P2 (O2 +N2), and P3 (3O+N2O) lie much lower than the reactants. Thus, the novel reaction N+NO2 can proceed effectively even at low-temperature and it is expected to play an important role in both combustion and interstellar processes. The reaction heats of formation calculated are in good agreement with that obtained experimentally. [Copyright &y& Elsevier]