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The UV absorption spectrum of all-trans-octatetraene is reinvestigated theoretically, focussing on the strongly dipole-allowed 1 A g – 1 B u transition. The dynamical calculations rely on ab initio multistate CASPT2 (MS-CASPT2) computations of the underlying potential energy surfaces and coupling elements, and the multiconfiguration time-dependent Hartree (MCTDH) method for solving the time-dependent Schrödinger equation for the nuclear motion. The vibronic structure of the absorption band near 2700 Å is well reproduced, better than ever before by a purely ab initio approach. The C–C single bond and C = C double bond stretching modes dominate the vibrational structure of the transition. While the latter resembles nearly harmonic motion on weakly coupled potential energy surfaces, the time-dependent calculations reveal a subpicosecond electronic population transfer from the 1 B u state to the lower-lying 2 A g state proceeding on a time scale of ∼ 50 fs . The details of this internal conversion process and its relation to the conical intersection between the two excited states are discussed, paying particular attention to the impact of the 1 B u – 2 A g energy gap on the dynamics. [ABSTRACT FROM AUTHOR]

A new global potential energy surface (PES) of the ground state of the HN2 system is built using the neural network method. The aug-cc-pVQZ basis set for the H atom, cc-pwCVQZ basis set for the N atom and multi-reference configuration interaction method are employed in the ab initio calculations. The topographic features of the PES are discussed and compared with available theoretical studies. In addition, the initial state (v0 = 0, j0 = 0) dynamic studies of the N + NH(³Σ -) → N2(X¹ Σg +)+H reaction are performed using a time-dependent wave packet method, based on the newly constructed PES. The dynamics properties, such as reaction probabilities, integral crosssections, differential cross-sections, the rovibrational state distribution of product and rate constants, are calculated at the state-to-state level of theory and compared with available theoretical and experimental results. The differential cross-section indicates that the forward abstraction mechanism dominates the reaction with the increase of collision energy. [ABSTRACT FROM AUTHOR]

The intermolecular potential energy surfaces (PESs) of Ne-CO complex have been constructed by using the CCSD(T)-F12a method with the aug-cc-pVQZ basis set. These PESs were subsequently applied to investigate the microwave and infrared spectra via bound state calculations. Firstly, compared to the available microwave data, the pure rotational transitions with K = 0 and J = 4 for this complex can be well reproduced. Furthermore, a set of accurate spectroscopic parameters were deduced for the fundamental (vCO = 1) and overtone (vCO = 2) bands. The vibrational shift for the normal isotopologue (Ne-12C16O) was determined to be -0.0683 cm-1, which is in excellent agreement with the experimental observation of -0.0711cm-1. Isotope effects were also investigated, and the determined rotational constants and vibrational shifts display a fairly good linear relationship, which is classified into two types according to the 12C and 13C in the CO monomer. [ABSTRACT FROM AUTHOR]

Based on 17,326 ab initio points, a global potential energy surface (PES) of the ground state of the CsH2 system was constructed using the neural network method. In ab initio calculations, the AVQZ basis set was used for the H atom, the def2-QZVP basis set was adopted for the Cs atom, and a multi-reference configuration interaction method was employed. The topographical characteristics of the newly developed PES were discussed in detail and no wells or barriers were detected. In addition, the dynamical calculations of the H + CsH reaction were performed using the time-dependent wave packet method, based on the new PES. Dynamics properties, such as reaction probability, integral cross section and differential cross-section were examined. The differential cross-section results indicated that the forward abstraction mechanism dominated the abstraction channel, and the 'rebound' reaction mechanism played a primary role in the exchange channel. Highlights Using the PIP-NN method, A global potential energy surface for the ground state of the CsH2 system was built based on 17,326 ab initio points. Dynamic calculations for the abstraction and exchange channels of the H + CsH reaction were performed using the time-dependent wave packet method and the dynamic properties of these two channels were discussed in detail. The direct abstraction mechanism plays a dominant role in the abstraction channel and the 'rebound' mechanism dominates the exchange channel. [ABSTRACT FROM AUTHOR]

Methyl isocyanate (CH3NCO) is an important agricultural and industrial precursor and emission from wildfires. In this paper, we study thermodynamic, kinetic and mechanistic approach of CH3NCO with OH radical and Cl atom using M06-2X level in combination with 6-311++G(d,p) basis set, and corrected by relatively accurate the single point CCSD(T) method. The rate constants of the title reactions are calculated in the temperature range of 200 and 400 K. The reactions exhibit a positive temperature depending on rate constants and fitted to the three-parameter Arrhenius expressions: kOH = 2.76 × 10−19 T2.65 exp[−486/T] and kCl = 3.51 × 10−18 T2.28 exp[95/T] with Wigner's and kOH = 4.95 × 10−19 T2.57 exp[−504/T] and kCl = 1.20 × 10−17 T2.11 exp[63/T] with Eckart's tunnelling corrections between 200 and 400 K. The calculated rate constants for the CH3NCO + OH/Cl reaction are in very good agreement with the previously reported experimental values. Thermochemical data (ΔH°298 K and ΔG°298 K) illustrate the feasibility and spontaneity of the title reactions. The atmospheric degradation mechanism of CH3NCO is discussed. The OH/Cl-driven tropospheric lifetimes and global warming potential (GWP) for CH3NCO were calculated. It was concluded that CH3NCO existed in the Earth's atmosphere for a few days and its GWP is not significantly large. The ozone formation potential of CH3NCO was also reported in this work. [ABSTRACT FROM AUTHOR]

The potential energy surface describing the interaction of methylene (CH 2 ) in its ground X ~ 3 B 1 electronic state with molecular hydrogen has been calculated through explicitly correlated coupled cluster theory with inclusion of single, double, and (perturbatively) triple excitations [RCCSD(T)-F12a] and a correlation-consistent aug-cc-pVTZ basis. The calculated points for various geometries of the CH 2 –H 2 complex were fit to a functional form suitable for use in time-independent quantum scattering calculations of cross sections for collision-induced transitions between CH 2 rotational levels. The well depth D e of the CH 2 –H 2 complex was found to equal 92.1 cm − 1 in a planar geometry and intermolecular separation R = 6.55 a 0 . A representative set of cross sections is presented and compared with cross sections for the corresponding transitions in methylene induced by collisions with helium. [ABSTRACT FROM AUTHOR]

Low-lying vibrational energy levels of both the ground (S0) and first excited singlet (S1) states of formaldehyde have been determined using an exact kinetic energy operator and adiabatic potential energy surfaces derived from a recently developed full-dimensional global diabatic potential energy matrix (DPEM) based on a neural network representation of high level ab initio data. The agreement with available experimental band origins provides strong evidence in support of the accuracy of the DPEM, which can be used in the future for understanding the internal conversion of H2CO(S1) and the subsequent roaming dynamics on its S0 state. [ABSTRACT FROM AUTHOR]

The reaction between O(3P) and H2O is of significance in combustion, atmospheric and interstellar chemistry. Using an accurate full-dimensional potential energy surface (PES) for the lowest triplet state of the H2O2 system, the quasi-classical trajectory method is employed to run dynamical simulations between O(3P) and H2O at hyperthermal collision energies of 50–100 kcal mol−1, which may access the hydrogen abstraction channel OH + OH, the hydrogen elimination channel H + HO2 and the oxygen exchange channel O + H2O. The integral cross sections (ICSs), differential cross sections, product energy/state distributions and reaction mechanisms are studied for the channels leading to products OH + OH and H + HO2. [ABSTRACT FROM AUTHOR]

This work presents a time-dependent wave packet investigation for the reaction N(2D) + H2(X1Σ+g) based on the new potential energy surface [Y. Q. Li and A. J. C. Varandas 2010 J. Phys. Chem. A 114 9644] of NH2(12A′) for the first time. The probability of reaction at the total angular momentum J = 0, 8, 16, 24, 30 and 45 are calculated as a function of collision energies with the range from 0.1 to 1.2 eV. The integral cross section obtained by Coriolis coupling is larger than the given by centrifugal sudden approximation, which shows that Coriolis coupling in this reaction cannot be ignored. Furthermore, the difference among the j-dependent integral cross sections indicates that N2 rotation promotes the reaction. [ABSTRACT FROM AUTHOR]

In this contribution, we investigate the nature of the electronic interaction between gas phase CO and NO with coinage metal atoms {Cu, Ag, Au} in different charge states. The electronic structure is first characterised by means of state-of-the-art coupled-cluster calculations for a wide range of configurations. An analytical Reactive Bond Order (REBO) force field is used to fit the data, revealing a strong corrugation of the potential energy landscape in some cases. The fundamental vibrational bands are variationally computed for the different system. It is found that the metal determines the binding interaction and the spectroscopic signature of the complexes, as well as their structure and geometry. [ABSTRACT FROM AUTHOR]

The excited-state intramolecular proton transfer (ESIPT) mechanisms of [2,2′-bipyridyl]-3,3′-diol (BP(OH)2) in gas are studied by using density functional theory (DFT) and time-dependent density functional theory (TDDFT) methods. The intramolecular hydrogen bond (H-bond) is strengthened in the first excited-state in view of the structural parameters and infrared (IR) vibrational frequencies. The enhanced intramolecular H-bond is favourable for ESIPT process. The effect of the extra intermolecular H-bond between BP(OH)2 and water on ESIPT is considered. The potential energy surfaces, molecular electrostatic potential, topological analysis, frontier molecular orbitals, absorption and fluorescence spectra are investigated. Our calculated results show that the intermolecular H-bond enhances the intramolecular H-bond, changes the mechanism and decreases the barrier height of ESIPT process. [ABSTRACT FROM AUTHOR]

We report a new four-dimensional potential energy surface for the C2H2–Ar complex involving the Q 1 and Q 3 normal modes for the v 1 symmetric stretching and v 3 asymmetric stretching vibration of the C2H2 molecule. The potential was constructed at the coupled-cluster singles and doubles with noniterative inclusion of connected triples [CCSD(T)]-F12 level with augmented correlation-consistent polarized-valence triple-zeta (aug-cc-pVTZ) basis set supplemented with midpoint bond functions (3s3p2d1f1g). Two vibrationally averaged potentials with C2H2 at the vibrational ground and v 1 + v 3 excited states were obtained by the integration of the potential over the Q 1 and Q 3 coordinates. It was found that each averaged potential has two equivalent T-shaped global minima, two equivalent local minima as well as three saddle points among them. The global minima are located at R = 3.97 Å, θ = 61.4°/118.6° with a well depth of 125.47 cm−1. The rovibrational energy levels and bound states were calculated adopting radial discrete variable representation (DVR)/angular finite basis representation (FBR) and the Lanczos algorithm. The calculated band origin for C2H2–Ar is red-shift by −0.9937cm−1 in the v 1 + v 3 region of C2H2, which reproduces the observed value of −1.0749cm−1 successfully. Furthermore, the calculated microwave and infrared transition frequencies are in well good agreement with the experiment data. [ABSTRACT FROM AUTHOR]

As an intermediate product of phosphorus compounds in astrophysical chemistry, PH 2 + (1 1 A ′) has great significance in research on the PH n + (n = 0 − 4) systems. However, as a basis for studying its reaction mechanisms, PH 2 + (1 1 A ′) lacks an accurate global potential energy surface (PES) and related dynamic reports. In this investigation, based on a multi-reference configuration interaction approach with Davidson correction, an accurate global many-body expansion PES for PH 2 + in its ground state was reported by fitting extensive ab initio energies, as calculated with the correlation-consistent basis set aug-cc-pVQZ. Meanwhile, the switching function formalism was adopted to explain and distinguish the transformation between P + ( 1 D) and P + ( 3 P) in one-body energy terms, which ensured the correct dissociation channel in the reaction process of P + ( 1 D) + H 2 ( {X} 1 Σ g +) → P H + ( X 2 Π) + H ( 2 S). The topographical characteristics of the title system PES were meticulously contrasted with those in other literature reports, which were consistent with previous experimental and theoretical values. Subsequently, the time-dependent wave packet approach was adopted to calculate the reaction probability and integral cross-section for the reaction P + ( 1 D) + H 2 ( {X} 1 Σ g +) (v = 0 , j = 0) → P H + ( X 2 Π) + H ( 2 S) to verify the accuracy of the new PES. This dynamics study may help to further explain the thermochemical reactions of phosphorus-containing molecules in interstellar media. [ABSTRACT FROM AUTHOR]

AlH 2 + has very important research significance as the intermediate product of free radical Al H 2 . However, in Bell and Simons's [J. Phys. Chem. A. 103, 539–549 (1999)] study about AlH 2 + , the maximum value of the integral cross section is about twice as large as the experimental value, which is caused by the lack of a precise global potential energy surface. An accurate full three-dimensional global potential energy surface for the electronic ground state of AlH 2 + is reported in this paper by fitting a large amount of ab initio energies extrapolated to the complete basis set limit, which calculated based on aug-cc-pV(Q,5)Z basis sets and the multi-reference configuration interaction method with Davidson correction. The main geomorphic features of the novel potential energy surface are carefully investigated and have a great agreement with previous works. For examining the correctness of the new potential energy surface, based on the reaction A l + ( 1 S) + H 2 ( 1 Σ g +) (υ = 0 , j = 0) → Al H + ( X 2 ∑ + ) + H ( 2 S) , the integral cross section is calculated by employing the time-dependent wave packet theory and quasi-classical trajectory method. The dynamic results of two methods are in good agreement with the experimental values, which indicates the novel potential energy surface perfectly solves the divergence between the theoretical and the experimental value. [ABSTRACT FROM AUTHOR]

A new six-dimensional potential energy surface for the Ar–H2S complex involving the Q 1 , Q 2 and Q 3 normal modes for the v 1 symmetric stretch vibration, v 2 bending vibration and v 3 asymmetric stretch vibration of H2S was reported. The potential was calculated at the coupled-cluster singles and doubles with non-iterative inclusion of connected triples [CCSD(T)]-F12a. The vibrationally averaged potentials with H2S at the vibrational ground state as well as the v 2 and v 3 excited states were generated from the six-dimensional potential. Each potential was found to have a planar T-shaped global minimum, a planar local minimum, two first-order saddle points and a second-order saddle point. The global minimum is located at R = 3.73 Å , θ = 113.5 ∘ and ϕ = 0.0 ∘ with a well depth of 179.24 cm−1. The radial discrete variable representation/angular finite basis representation method and the Lanczos algorithm were employed to calculate the rovibrational energy levels for Ar–H2S with H2S at the vibrational ground and excited states. The predicted vibrational band origins are redshift by −0.38 and −0.63 cm−1 of the Ar–H2S in the v 2 and v 3 regions of H2S, respectively. The rotational frequencies were in good agreement with the experimental values, which were within 0.5% of the observed dates. [ABSTRACT FROM AUTHOR]

Electronic structure calculations are carried out for the S4 molecule at the CCSD(T)-F12a/VTZ-F12 level of theory to map out its potential energy surface, which possesses a double-well shape with a low-energy barrier. Two degrees of freedom are considered: the distance R and the gearing motion angle between the two weakly-perturbed S2 dimers, which form S4. Vibrational states are computed on this 2D-surface and assigned quantum numbers based on their energies and the shapes of their wave functions. Two progressions of vibrational states are identified: a long progression of easily assignable states that develop nodes along the 'channels' on the surface, and a shorter progression of states that develop nodes across the 'channels' and are much harder to assign, due to the double-well effect. Normal mode analysis indicates that these two modes in S4 represent a significant mixture of conventional bending and stretching motions. When the angle is increased, the lower frequency mode corresponds to stretching of the distance R, while the higher frequency mode corresponds to compression of R. Frequencies of the modes, ∼180 and ∼420 cm−1, are in a qualitative agreement with earlier ab initio studies of tetra-sulfur, and with sparse experimental data. [ABSTRACT FROM AUTHOR]

A globally correct potential energy surface (PES) for the molecular ion is presented. The Born-Oppenheimer (BO) ab initio grid points of Pavanello et al. [J. Chem. Phys.136, 184303 (2012)] are refitted as BOPES75K, which reproduces the energies below dissociation with a root mean square deviation of 0.05 cm−1; points between dissociation and 75,000 cm−1 are reproduced with the average accuracy of a few wavenumbers. The new PES75K+ potential combines BOPES75K with adiabatic, relativistic and quantum electrodynamics (QED) surfaces to provide the most accurate representation of the global potential to date, overcoming the limitations on previous high accuracy PESs near and above dissociation. PES75K+ can be used to provide predictions of bound rovibrational energy levels with an accuracy of approaching 0.1 cm−1. Calculation of rovibrational energy levels within PES75K+ suggests that the non-adiabatic correction remains a limiting factor. The PES is also constructed to give the correct asymptotic limit making it suitable for use in studies of the prototypical chemical reaction. An improved dissociation energy for is derived as cm−1. [ABSTRACT FROM AUTHOR]

A 5-D compound-model morphed potential has been generated for the prototype hydrogen-bonded dimer HCN⋯HF. The potential includes the intermolecular degree of freedom and the HF stretching vibration. Only five morphing parameters are optimised, correcting for inadequacies in the underlying ab initio potentials. Band origin fundamental vibrational frequencies are fitted to an average absolute error of 0.01 cm−1. The calculated value of the ground state dissociation energy, D0 = 1969 cm−1, is in excellent agreement with the experimental value of 1970(10) cm−1 [Oudejans and Miller, Chem. Phys. 239 (1998) 345]. Additional vibrational frequencies are predicted with an average absolute error of 1.61 cm−1. Application of the morphing methodology to characterise hydrogen-bonded complexes is discussed. [ABSTRACT FROM AUTHOR]

In this contribution, we reinvestigate the interaction of nitric oxide with a gold(111) surface using plane-wave density functional theory, with particular emphasis on the role of intermode coupling. A new global representation of the potential energy surface is obtained from the ab initio data by non-linear adjustment, yielding a set of physically motivated parameters. The novel functional form improves on its parent [Marquardt et al. J. Chem. Phys. 132, 074108 (2010)] by addressing the variation of the charge transfer character of the electronic structure data, and by treating surface corrugation via translationally invariant weighting functions of lower-dimensional, high-symmetry sites. Contrary to previous studies, the adsorption minimum does not favour the hollow sites and is found at a strongly tilted orientation (circa 60) on top of a gold atom of the topmost layer. High-dimensional anharmonic vibrational analysis performed using a Lanczos-based contracted iterative procedure reveals that the low-lying excited vibrational states retain a strongly tilted orientation and remain predominantly localised at the atop site. These findings are expected to have important implications for the interpretation of recent NO scattering experiments. [ABSTRACT FROM AUTHOR]

We report a new full-dimensional ab initio potential energy surface for the Ar-HF van der Waals complex at the level of coupled-cluster singles and doubles with noniterative inclusion of connected triples levels [CCSD(T)] using augmented correlation-consistent quintuple-zeta basis set (aV5Z) plus bond functions. Full counterpoise correction was employed to correct the basis-set superposition error. The hypersurface was fitted using artificial neural network method with a root mean square error of 0.1085 cm−1 for more than 8000 ab initio points. The complex was found to prefer a linear Ar-H-F equilibrium structure. The three-dimensional discrete variable representation method and the Lanczos propagation algorithm were then employed to calculate the rovibrational states without separating inter- and intra- molecular nuclear motions. The calculated vibrational energies of Ar-HF differ from the experiment values within about 1 cm−1 on the first four HF vibrational states, and the predicted pure rotational energies on (0000) and (1000) vibrational states are deviated from the observed value by about 1%, which shows the accuracy of our new PES. [ABSTRACT FROM AUTHOR]

Gaussian process regression (GPR) is an efficient non-parametric method for constructing multi-dimensional potential energy surfaces (PESs) for polyatomic molecules. Since not only the posterior mean but also the posterior variance can be easily calculated, GPR provides a well-established model for active learning, through which PESs can be constructed more efficiently and accurately. We propose a strategy of active data selection for the construction of PESs with emphasis on low energy regions. Through three-dimensional (3D) example of H3, the validity of this strategy is verified. The PESs for two prototypically reactive systems, namely, H + H2O ↔ H2 + OH reaction and H + CH4 ↔ H2 + CH3 reaction are reconstructed. Only 920 and 4000 points are assembled to reconstruct these two PESs respectively. The accuracy of the GP PESs is not only tested by energy errors but also validated by quantum scattering calculations. [ABSTRACT FROM AUTHOR]

A novel global potential energy surface for H2S+(X 4A″) based on accurateab initiocalculations is presented. Energies are calculated at the multi-reference configuration interaction level with Davidson correction using aug-cc-pVQZ basis set plus core-polarisation high-exponent d functions. A grid of 4552 points is used for the least-square fitting procedure in the frame of a many-body expansion. The topographical features of the new potential energy surface are here discussed in detail. Such a surface is then employed for dynamic studies of the S(4S) + H2(X 1Σ+g) →SH+(X 3Σ−) + H(2S) reaction using the quasi-classical trajectory method. State specific trajectories are calculated, for both ground and ro-vibrationally excited initial states of H2(X 1Σ+g). Corrections to the zero point energy leakage of the classical calculations are also presented. Calculated reaction cross sections and rate constants are here reported and compared with available literature. [ABSTRACT FROM PUBLISHER]

In this work, we propose an algorithm for calculating the matrix elements of the kinetic energy operator for tetrahedral molecules. This algorithm uses the dependent six-angle coordinates (6A) and takes into account the full symmetry of molecules. Unlike A.V. Nikitin, M. Rey, and Vl. G. Tyuterev who operate with the kinetic energy operator only in Radau orthogonal coordinates, we consider a general case. The matrix elements are shown to be a sum of products of one-dimensional integrals. [ABSTRACT FROM PUBLISHER]

A new four-dimensional (4D)ab initiopotential energy surface (PES) for Ne–CS2involving theQ1andQ3normal modes for the ν1symmetric stretching vibration and ν3antisymmetric stretching vibration of CS2is presented. The PES is constructed at the coupled-cluster singles and doubles with noniterative inclusion of connected triples [CCSD(T)]-F12 level with a large basis set including midpoint bond functions. Two vibrationally averaged potentials with CS2at the vibrational ground and ν1+ ν3excited states are generated from the 4D potential. Each potential contains a T-shaped global minimum and two equivalent linear local minima. The rovibrational energy levels and bound states are calculated employing radial discrete variable representation/angular finite basis representation and the Lanczos algorithm. In addition, the predicted band origin shift is 0.2514 cm−1for Ne–CS2. The spectroscopic parameters are also predicted. [ABSTRACT FROM AUTHOR]

The rotational spectrum of 3-pentyn-1-ol, CH3−C≡C−CH2CH2OH, was measured using a molecular beam Fourier transform microwave spectrometer operating in the frequency range from 2 to 26.5 GHz. A two-dimensional potential energy surface was calculated at the MP2/6-311++G(d,p) level of theory for a conformational analysis, yielding five conformers. The most stable conformer exhibits C1symmetry and was assigned in the spectrum by comparison with the results from quantum chemical calculations. The barrier to internal rotation of the propynyl methyl groupCH3−C≡C− was found to be only 9.4552(94) cm−1. Molecular parameters and internal rotation parameters could be accurately determined using the programxiamandbelgi-C1. The internal rotation barrier was compared with those of other molecules containing a propynyl methyl group. [ABSTRACT FROM AUTHOR]

The current work is a theoretical study of the tautomerism of thymine in the gas phase. Eighteen structures were found in the isomerisation reaction of thymine, some of which are reported for the first time. Thirty hydrogen transfer reactions were carried out. In 24 of the reactions, the hydrogen abstractions N―H→O, N―H→C and C―H→O were considered. The potential energy surface for all trajectories was determined for 18 tautomers and 40 transition states. The RRKM-TST model was used to calculate the rate constants of the reactions to examine their kinetics. Nonlinear least-squares fitting was used to calculate the rate constants expressions. The interaction of sodium ion and tautomers in the gas phase was also investigated. Three types of interaction of metal cations with thymine were found. In the first, metal cations interact with a lone pair of nitrogen or oxygen tautomers. The second type is the interaction of metal cations with two nitrogen and oxygen of tautomers. The last type is the interaction of metal cations and the electron density of the π-system of thymine in which the metal ion is perpendicular to the ring of tautomers. The stability ranking of the thymine tautomers and their complexes was also determined. [ABSTRACT FROM PUBLISHER]

Rate constants for the reactions of C2H6, C2H5D and C2D6with.CCl3. for the production of CHCl3and CDCl3(k1,k2,k3andk4) were computed using variational transition state theory coupled with hybrid-meta density functional theory (MPWB1K) over the temperature range of 200–2900 K. The ground-state vibrational adiabatic potential was plotted for all channels. Small- and large-curvature tunnelling were determined to include quantum effects in the calculation of rate constants. Harmonic vibrational frequencies along the reaction path were calculated in curvilinear coordinates with scaled frequencies. Anharmonicity was included in the lowest-frequency torsion. The position of formation and dissociation of bonds was specified using the variation in harmonic vibrational frequencies along the reaction path. Representative tunnelling energy and the thermally averaged transmission probability at 298 K (P(E)exp ( − ΔE/RT)) were determined for the reactions in which tunnelling is important. The kinetic isotope effect was used to calculate the considerable contributions of tunnelling and vibration. The expressions for rate constants were determined using nonlinear least-square fitting over the temperature range of 200–2900 K. [ABSTRACT FROM AUTHOR]

A new three-dimensional potential energy surface (PES) of the Ar–N2van der Waals complex is constructed using the neural network method based onab initiodata points at the CCSD(T) level. The aug-cc-pVQZ basis set is employed for all atoms with midbond functions. The vibrationally averaged PESV00is characterised by a global T-shaped minimum which occurs atR=3.715 Å, θ = 90.0° with a well depth of 98.779 cm−1. Based on our three-dimensional PES, bound-state calculations are performed for three isotopomers of Ar–14N2, Ar–15N2, and Ar–14N15N, and several intermolecular vibrational states are assigned by analysing the wavefunctions. Moreover, the averaged structural parameters are calculated and the pure rotational transition frequencies withJ= 0--6 are predicted. The spectroscopic constants are determined by fitting the rotational energy levels. The theoretical results are in good agreement with experimental data and this work gives more accurate results than those determined previously for the Ar–N2complex. [ABSTRACT FROM AUTHOR]

An accurate near-equilibrium potential energy surface (PES) for CNC+is constructed based on a high-level compositeab initiomethod. By combining explicitly correlated all-electron CCSD(T)-F12b with scalar relativistic effects and higher order correlation up to coupled cluster theory with singles, doubles, triples and quadruples (CCSDTQ) we achieve convergence in the wavenumbers of the fundamentals to ca. 1 cm−1. Rovibrational energies are calculated in a variational approach and vibrational term energies and rotational constants are in excellent agreement with available experimental data. Accurate values for centrifugal distortion constants of CNC+in different vibrational states are predicted. Especially the centrifugal distortion constants in the vibrational ground state ofD0= 0.563 · 10−6cm−1andH0= 0.188 · 10−10cm−1should be superior to experimentally derived values. Reassignments of some experimentally observed transitions are suggested based on a comparison of experimental and calculated term differences. The bending part of the PES appears to be almost quartic and the band origin of the bending vibration is predicted at 94.2 cm−1. Absolute line intensities are calculated for various transitions in CNC+. For the bending vibration, an intensity is predicted that is three orders of magnitude smaller than for the antisymmetric stretching vibration. [ABSTRACT FROM PUBLISHER]

A data-set of nearly 100,000 symmetry unique multi-configurationalab initiopoints for methane were generated at the (AE)-MRCI-F12(Q)/CVQZ-F12 level, including energies beyond 30,000 cm−1above the minimum and fit into potential energy surfaces (PESs) by several permutation invariant schemes. A multi-expansion interpolative fit combining interpolating moving least squares (IMLS) fitting and permutation invariant polynomials (PIP) was able to fit the complete data-set to a root-mean-square deviation of 1.0 cm−1and thus was used to benchmark the other fitting methods. The other fitting methods include a single PIP expansion and two neural network (NN) based approaches, one of which combines NN with PIP. Full-dimensional variational vibrational calculations using a contracted-iterative method (and a Lanczos eigensolver) were used to assess the spectroscopic accuracy of the electronic structure method. The results show that the NN-based fitting approaches are able to fit the data-set remarkably accurately with the PIP–NN method producing levels in remarkably close agreement with the PIP–IMLS benchmark. The (AE)-MRCI-F12(Q)/CVQZ-F12 electronic structure method produces vibrational levels of near spectroscopic accuracy and a superb equilibrium geometry. The levels are systematically slightly too high, beginning at ∼ 1–2 cm−1above the fundamentals and becoming correspondingly higher for overtones. The PES is therefore suitable for smallab initioor empirical corrections and since it is based on a multi-reference method, can be extended to represent dynamically relevant dissociation channels. [ABSTRACT FROM PUBLISHER]

We present a study on the performance of our iterative triples correction for the coupled cluster singles and doubles excitations (CCSDT-1a+d) method for computation of potential energy surface (PES), spectroscopic constants, and vibrational spectrum for the ground state (X1Σ+) BeMg, where the ostensible inadequacy of the CCSD and CCSD(T) methods is quite expected. We compare our results with those obtained using state-of-the-art multireference configuration interaction (MRCI) investigations reported earlier by Kerkines and Nicolaides. Our estimated dissociation energy (417.37 cm−1), equilibrium distance (3.285 Å), and vibrational frequency (82.32 cm−1) are in good agreement with recent results of advanced MRCI calculations forX1Σ+BeMg PES, which exhibits a shallow well of 469.4 cm−1with a minimum at 3.241 Å and a harmonic vibrational frequency of 85.7 cm−1. Very weakly bound nature ofX1Σ+BeMg is clearly reflected from these values. In accord with MRCI studies, a comparison of BeMg with iso-valence weakly bound ground-state species, Be2and Mg2, suggests that its characteristics do not exhibit any resemblance to Be2rather, it shows a close kinship to Mg2. The agreement of our derived vibrational levels with those obtained via the high-level MRCI calculations is very encouraging reflecting the potential of the suitably modified single-reference coupled cluster (SRCC) method, CCSDT-1a+d as a tool for the study of multireference van der Waals systems. [ABSTRACT FROM AUTHOR]

In order to rigorously evaluate the energy and dipole moment of a certain configuration of molecules, one needs to solve the Schrödinger equation. Repeating this for many different configurations allows one to determine the potential energy surface (PES) and the dipole moment surface (DMS). Since the early days of computer simulation, it has been implicitly accepted that for empirical potentials the charges used to fit the PES should also be used to describe the DMS. This is a mistake. Partial charges are not observable magnitudes. They should be regarded as adjustable fitting parameters. Optimal values used to describe the PES are not necessarily the best to describe the DMS. One could use two fits: one for the PES and the other for the DMS. This is a common practice in the quantum chemistry community, but not used so often by the community performing computer simulations. This idea affects all types of modelling of water (with the exception ofab initiocalculations) from coarse-grained to non-polarisable and polarisable models. We anticipate that an area that will benefit dramatically from having both, a good PES and a good DMS, is the modelling of water in the presence of electric fields. [ABSTRACT FROM PUBLISHER]

In this work, the excited state intermolecular potential energy surface of the Ar–CS2(V1B2) van der Waals complex was evaluated for the first time. The calculation of more than 4000 single-point interaction energies for the complex using an equation-of-motion coupled-cluster model with single and double substitutions level of theory with extended basis set involving bond functions has been performed. After fitting the interaction energies to analytical functions, the emission spectra of the Ar–CS2(V1B2) complex related to the different stationary points on the potential energy surface were calculated. It was seen that the intensity and the position of the emission spectra are dependent on the orientation of the Ar atom around the bent excited CS2and the distance between two components. The information about the structural parameters of the complex related to the global minimum was obtained under the pseudodiatomic approximation with assistance ofab initiopotential. The presented investigation could be useful for further theoretical and experimental studies of Ar–CS2(V1B2) complex. [ABSTRACT FROM AUTHOR]

Application of Hamilton–Jacobi (HJ) equation to reaction systems which involve energy barrier(s) leading to the product is relatively new. Such problems are described by a new class of HJ equation, called the generalised HJ equation. This new HJ equation renders an anisotropic propagation for the wave front. In this paper, we describe the adaptation of the fast marching method (FMM) and the generalised HJ equation to understand a new class of reaction process where the energy barrier does not lead to the product; instead, a new class of states are detected along the reaction path of such reactions. These states are valley-ridge inflection point, branching point and potential energy ridge. Such reactions are characterised as bifurcation reactions. We have identified a new classical wave front, called the reaction action front (RAF) which distinctly separates the reaction system into a reactant zone and a product zone connected by a third zone, called ‘neck’. The RAF is an important tool to understand the bifurcation reaction and the associated reaction paths. We have also introduced a convenient way to compute the reaction path force (RPF) using the FMM. The RPF for a bifurcation reaction significantly differs from the reactions with energy barrier, and so, the RPF provides vital information about the occurrence of branching of a path. The method has been tested for the isomerisation reaction of methoxy radical (H3C) to hydroxymethylene radical (H2ĊOH). [ABSTRACT FROM AUTHOR]

Coulson–Fischer theory is applied to the ground electronic state of the simplest polyatomic molecule, the H+3molecular ion. The Coulson–Fischer orbitals are parametrised in terms of a distributed Gaussian basis set ofs-type functions with variationally optimised exponents and positions. The efficacy of these basis set is demonstrated by performing matrix Hartree–Fock calculations which can be compared with previous studies using alternative methods of basis set construction. The ground-state potential energy surface is explored for a range of equilateral, isosceles and scalene triangular geometries for which a number of authors have reported the results of accurate calculations. It is demonstrated that the Coulson–Fischer wave function supports a global approximation to the ground-state potential energy surface of the H+3system. The Coulson–Fischer orbitals afford a simple picture of the molecular wave function which provide a simple description of the bonding for all geometries. The distributed Gaussian basis set affords a more efficient method of approximation than some other techniques, such as, for example, the more widely used expansions in terms of atom-centred basis functions. [ABSTRACT FROM AUTHOR]

The exact nuclear time-dependent potential energy surface arises from the exact decomposition of the electronic and nuclear motions, recently presented in [A. Abedi, N.T. Maitra, and E.K.U. Gross, Phys. Rev. Lett. 105, 123002 (2010)]. Such time-dependent potential drives nuclear motion and fully accounts for the coupling to the electronic subsystem. We investigate the features of the potential in the context of electronic non-adiabatic processes and employ it to study the performance of the classical approximation on nuclear dynamics. We observe that the potential, after the nuclear wave packet splits at an avoided crossing, develops dynamical steps connecting different regions, along the nuclear coordinate, in which it has the same slope as one or the other adiabatic surface. A detailed analysis of these steps is presented for systems with different non-adiabatic coupling strength. The exact factorisation of the electron-nuclear wave function is at the basis of the decomposition. In particular, the nuclear part is the true nuclear wave function, solution of a time-dependent Schrödinger equation and leading to the exact many-body density and current density. As a consequence, the Ehrenfest theorem can be extended to the nuclear subsystem and Hamiltonian, as discussed here with an analytical derivation and numerical results. [ABSTRACT FROM AUTHOR]

Tentative assignment of the low-lying vibrational features of the first electronic excited singlet-state S1of diphenyl ether (Ph2O), obtained from resonance-enhanced multiphoton ionisation (REMPI) spectroscopy, is performed using CIS and time-dependent density functional theory (TD-DFT) methods. The potential energy surfaces, regarding the rotation of the phenyl rings relatively to the C–O–C plane, are obtained at the B3LYP/6-31G(d) level of theory, for the ground-state of neutral and cationic Ph2O and for its first excited singlet state. The torsional barriers of the ground state of diphenyl ether were studied by means of quantum-chemical perturbations of increasing accuracy and an extrapolation to the complete basis set limit and full configuration interaction (FCI) was performed through the use of correlation consistent basis sets and the continued fraction method. The first adiabatic ionisation energy (AIE) of thetwistconformer is computed at 8.60 eV in the FCI limit, much higher than the experimental results of Terlouwet al.(8.09±0.03 eV) and Paivaet al.(7.8±0.1 eV). The B3LYP result of 7.82 eV is, however, in reasonable agreement with the result of Paivaet al.The first singlet excitation energy for thetwistconformation is found to be 5.5 eV at the CIS/6-311++G(d,p) level of theory. Some features of the experimental REMPI spectrum, previously obtained by one of the authors, are explained and a new insight on the ionisation energy of diphenyl ether is presented. [ABSTRACT FROM AUTHOR]

We introduce a new tool for reaction pathway analysis based on a chemical bonding density descriptor obtained from the higher resolution Poincaré–Hopf relation. To remove the degeneracy of the Poincaré–Hopf relationship for critical points of the electron density, we introduce the concepts of bonding cardinality and characterise the topology of rings and cages. This allows us to relate the changes in the relative energetic stability along an isomerisation reaction pathway with changes in the topology of the electron density. To demonstrate the utility of this approach, we consider the complete circuit of the reaction pathway connecting the various Möbius and Hückel structures in Au and/or Pd bis-metallated octaphyrins. Where the topological feature ‘cages’ exist in adjacent topologies, the degeneracy in the Poincaré–Hopf relationship is completely removed even for differences in relative energies of only 0.1 kcal/mol. Metallation of the Möbius and Hückel structures was found to increase the topological complexity and bonding density. Combining Pd and Au nuclei in the octaphyrin complexes reduced the smoothness of the potential energy surface. The presence of long, weak C–H contacts correlates in all cases with the lowest energy enantiomers and the most negative nuclear-independent chemical shift values of the reaction pathways in Au and/or Pd bis-metallated octaphyrins. [ABSTRACT FROM AUTHOR]

The structure and properties of the cyclopropene radical cation c-C3H+•4are investigated by means of quantum chemical methods. The equilibrium geometry of c-C3H+•4is found to haveC2symmetry and a low barrier of 470 cm−1for stereomutation (around 700 cm−1, including ZPVE corrections) with a transition state ofC2vsymmetry. The adiabatic ionisation potential is estimated to be 77,800 cm−1with respect to c-C3H4. Vertical ionisation potential energies of c-C3H4, and vertical excitation energies to low-lying excited states of c-C3H+•4are presented. [ABSTRACT FROM AUTHOR]

An accurate,ab initiopotential energy surface (PES) is reported for CH3OH including the bound region as well as the barrierless dissociation to CH3+OH. The surface is a linear least-squares fit to a total of 45,199ab initioenergies, most of which were computed using CCSD(T)-F12b/aug-cc-pVDZ theory and a small number using CASPT2/aug-cc-pVDZ theory. The latter set was done in the multi-reference region of the PES in order to obtain a realistic description of the OH–CH3interaction in the near asymptotic region. The geometries and harmonic frequencies of the stationary points agree very well with direct CCSD(T)-F12b calculations. The three-fold barrier to internal rotation of CH3OH is also accurately described by the PES. The zero-point energies of methanol and CH3+OH are determined by Diffusion Monte Carlo calculations. The D0dissociation energy is 90.1 kcal/mol, in very good agreement with the recent IUPAC evaluation [Ruscicet al., J. Phys. Chem. Ref. Data34, 573 (2005)] result of 90.25 kcal/mol. [ABSTRACT FROM AUTHOR]

Theoretical investigations are carried out on the title reactions by means ofab initioand DFT methods. The optimized geometries, frequencies and minimum energy path are obtained at MPWB1K/6-31+G(d,p) level. Single point energy calculations are performed at MP2 and QCISD(T) levels of theory. Energetics were further refined by calculating the energy of the species with a high level G2(MP2) method. The rate constant of the two reactions are calculated at 298 K and 1 atm using Canonical Transition State Theory (CTST) utilizing theab initiodata obtained during the present study. The rate constant values are found to be 5.5 × 10−14and 5.9 × 10−14 cm3molecule−1s−1, respectively which are in good agreement with the experimental data. [ABSTRACT FROM PUBLISHER]

The potential energy surfaces of the He–CS2, Ne–CS2and Ar–CS2van der Waals complexes were calculated for the first time at the CCSD(T) level of theory using the aug-cc-pVDZ basis set augmented with a set of midbond functions (3s3p2d1f1g). It was found that the calculated interaction potential, using the applied basis set, readily converges to the complete basis set limit. For a broad range of intermolecular separations and configurations, the interaction energies were obtained by the supermolecular approach with the full counterpoise correction for the basis set superposition error (BSSE). In addition, symmetry-adapted perturbation theory (SAPT) calculations were performed with the same basis set in order to determine the character of the interaction energy of the most stable configuration of each complex at different intermolecular separations in order to make a comparison with the CCSD(T) results. The CCSD(T) calculated potential energy surface of each complex was fitted to an analytic expression to obtain the values of the isotropic dipole–dipole () and dipole–quadruple () dispersion coefficients of each complex. Finally, the interaction second virial coefficients (B12) were obtained using the calculated potential energy surface and used together with the experimental second virial coefficients of pure gases (CS2, Ar, Ne and He) to obtain the second virial coefficient of mixtures of CS2with rare gas at different temperatures and mole fractions. [ABSTRACT FROM AUTHOR]

The three-dimensionalab initiopotential energy surface of the Kr–N2O complex was developed at the coupled-cluster single and double with non-iterative treatment of triple excitations [CCSD(T)] level. The potential includes explicit dependence on thesymmetric stretching coordinateof the N2O molecule. Two vibrationally averaged potentials with the N2O molecule at both the ground and the first vibrationalexcited states are generated. Dynamical calculations are performed to determine the bound state energies. The resulting potentials provide a good representation of the experimental data: for 119 infrared transitions of the84Kr–N2O complex, the root mean square deviation is only about 0.078 cm−1. The predicted rotational constants of the four isotopomers are also in good agreement with their experimental counterparts. [ABSTRACT FROM AUTHOR]

The structures, energetics and stability of the [P, X, Y] (X = C, Si; Y = O, S) radicals are explored by means of the density functional theory andab initiolevels. Seventeen [P, X, Y] isomers and 14 interconversion transition states are obtained at the B3LYP/6-311G(d) level. At the CCSD(T)/6-311 + G(2df)//QCISD/6-311G(d) + ZPVE level, the lowest-lying isomers are the linear PCO1a(0.0 kcal/mol), PCS1b(0.0) and the three-membered ring cPSiO1c(0.0), cPSiS1d(0.0) on their respective potential energy surfaces. These four isomers exhibit considerably not only thermodynamic but also kinetic stabilities. Additionally, the cyclic cPCS2b(32.8) and linear PSiS2d(18.6) possess also high kinetic stability. All of six isomers1a,1b,2b,1c,1dand2dare considerably stabilized by a barrier of at least 20 kcal/mol, and may be detected in the laboratory or interstellar space. Their valence bond structures and possible formation strategies in the laboratory and space are discussed in detail. Finally, the similarities and discrepancies on structures and stabilities between [P, X, Y] (X = C, Si; Y = O, S) isomers are compared. These predicted results are highly expected to be informative for the future identification of [P, X, Y] (X = C, Si; Y = O, S) in the laboratory and space. [ABSTRACT FROM PUBLISHER]

An ab initio potential energy surface determined at the CCSD(T) level of theory is presented for the van der Waals complex C2H2–N2. Additional calculations performed with the HF- and DFT- SAPT methods compare well with the CCSD(T) results and allow a better understanding of the main features of this interaction potential surface. An expansion of this surface over spherical harmonics has also been performed. The global energy minimum of the complex is obtained for the linear conformation. The T conformations are the least attractive. Such characteristics mainly arise because of the variation, in sign and in absolute value of the electrostatic energy between all these conformations. The specific role of the quadrupole–quadrupole interaction which involves two moments of opposite signs is therefore examined. The main features derived from the present surface are compared and discussed according to the following relevant systems: N2–H2, C2H2–H2, C2H2–C2H2 and N2–N2. Calculated rotational constants for selected conformations of the C2H2–N2 dimer are found to be in good agreement with available values. [ABSTRACT FROM AUTHOR]

Accurate ab initio intermolecular potential energy surfaces (IPES) have been obtained for the first time for the ground electronic state of the C2H2–Kr and C2H2–Xe van der Waals complexes. Extensive tests, including complete basis set and all-electron scalar relativistic results, support their calculation at the CCSD(T) level of theory, using small-core relativistic pseudopotentials for the rare-gas atoms and aug-cc-pVQZ basis sets extended with a set of 3s3p2d1f1g mid-bond functions. All results are corrected for the basis set superposition error. The importance of the scalar relativistic and rare-gas outer-core (n–1)d correlation effects is investigated. The calculated IPES, adjusted to analytical functions, are characterized by global minima corresponding to skew T-shaped geometries, in which the Jacobi vector positioning the rare-gas atom with respect to the center of mass of the C2H2 moiety corresponds to distances of 4.064 and 4.229 Å, and angles of 65.22° and 68.67° for C2H2–Kr and C2H2–Xe, respectively. The interaction energy of both complexes is estimated to be −151.88 (1.817 kJ mol−1) and −182.76 cm−1 (2.186 kJ mol−1), respectively. The evolution of the topology of the IPES as a function of the rare-gas atom, from He to Xe, is also discussed. [ABSTRACT FROM AUTHOR]

Much recent interest has focused on the understanding of the borane analogues of alanes. Being potential hydrogen-storage species, smaller alanes are also precursors or key intermediates of larger alanes. However, here we show that even for the simple trialane Al3H7, our knowledge is far from sufficient. Early low-level calculations considered an Al3-chain (classical) isomer and a less-stable Al3-ring (non-classical) isomer, indicative of the non-borane analogue of Al3H7. In the present work, we locate 11 new Al3H7 isomers within 15 kcal mol-1 and construct the first isomerization potential energy surface of Al3H7 at the G3B3///B3PW91/TZVP level. It is shown that the lowest-energy isomer of Al3H7 (Al-1) has a non-classical structure with an Al3 ring, similar to B3H7. Therefore, according to the Al3-ring skeleton, Al3H7 can be viewed as the borane analogue. Moreover, the second (Al3-ring, non-classical, Al-2) and third (Al3-chain, classical, Al-3) low-lying Al3H7 isomers lie only 2.04 and 4.31 kcal mol-1, respectively, above the ground isomer Al-1, and are separated from each other by barriers of around 10.0 kcal mol-1. Thus, in low-temperature matrix experiments, the three Al3H7 isomers (Al-1, Al-2 and Al-3) might all be observable. The difference between the trialane and triborane (X3H7, X = Al, B) is also disclosed, i.e. for X = Al, the X3-ring isomer with one XH2 is more stable than that with two or three XH2, whereas the case is the opposite for X = B. The calculated spectroscopic properties at the CCSD/TZVP level should provide useful information for future laboratory identification of Al-1, Al-2 and Al-3, the possible formation strategies of which are also discussed. [ABSTRACT FROM AUTHOR]

The potential energy surfaces provided by the coherent states formalism for the case of interacting one-dimensional oscillators is investigated. The case of two interacting oscillators modelled with Morse potentials are considered in detail. First the traditional treatment is presented in order to identify the need to establish a new transformation between the parameters and the classical variables that allow the full Hamiltonian to be recovered. To this end the connection between the su(2) algebraic model and the usual treatment in configuration space was taken into account. It is shown that the coherent state approach when applied to recover the potential energy surface (PES) from a polyad preserving Hamiltonian is viable only in systems with a local mode behaviour. For molecules with a normal mode behaviour the approach is still valid, but the polyad must be broken in order to recover the PES. Our approach is evaluated through the calculation of the force constants for H2O and CO2, representative examples of local and normal behaviours. [ABSTRACT FROM AUTHOR]

Despite the fact that B3O is the second simplest BnO radical after BO, a controversy recently emerged concerning the molecular structure of its global minimum. Two recent theoretical groups predicted the linear quartet BBBO to be the ground isomer. By contrast, another recent theoretical group reported that B3O has a doublet B3-ring ground structure. Moreover, larger BnO clusters usually have low-lying B3-ring isomers. In order to determine the accurate energetic competition between linear and cyclic structures in both the doublet and quartet, and to understand the detailed isomerism between various isomers, which is vital for understanding the formation mechanism of B3O, we report the first potential energy surface (PES) study of B3O at various computational levels, including CCSD(T)/6-311+G(2df), CCSD(T)/aug-cc-pVTZ, CCSD(T)/aug-cc-pVQZ and G3B3 for the single-point energy, as well as B3LYP/6-311+G(d) and QCISD/6-311+G(d) for geometrical optimisation. It is shown that the isomers in the quartet state are all thermodynamically more stable than the corresponding doublet ones, and on both the quartet and doublet PESs, the linear form has the lowest energy. Therefore, our study on both linear and cyclic isomers shows that the linear quartet BBBO 401 is definitively the ground isomer. Although being much less stable than the quartet linear BBBO global minimum by >20 kcal mol-1, five cyclic isomers exist as local minima, with the bi-cyclic structure 402 possessing the smallest barrier of around 15 kcal mol-1. The dissociation energies for direct combination processes B3 + O, B2 + BO and B + B2O are discussed. The present work may be helpful in obtaining a deep understanding of the doping and oxidation process of pure Bn clusters. [ABSTRACT FROM AUTHOR]

The intermolecular potential energy surface for C3-He complex has been constructed using supermolecular CCSD(T) and MP4 methods. The potential surfaces have been calculated for 27 values of R ranging from 2.8 to 8.0 Å and 19 values of θ equally spaced between 0° and 180°. Both CCSD(T) and MP4 potentials have similar global behaviors. The global minimum in each of the potentials corresponds to the slightly distorted T-shaped geometry. On the basis of these two potentials, the intermolecular vibrational energies and wavefunctions were calculated. The energy level pattern of the vdW vibrational states was predicted for C3-He complex. The zero point bending motion of this complex has a range of 180°. The calculated fundamental frequency of vdW bending is 3.16 cm-1 at CCSD(T) level, and 5.38 cm-1 at the MP4 level. In addition, we have also constructed the intermolecular potential energy surface with C3 bending coordinate of 160° by using supermolecular CCSD(T) method. Two local minima including arrow-shaped and Y-shaped configurations were determined. The rotational constants of three C3-He structures including T-shaped, arrow-shaped and Y-shaped configurations at CCSD(T) level were also reported. [ABSTRACT FROM AUTHOR]