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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. [ABSTRACT FROM AUTHOR]

In this paper, we performed a theoretical study on the influence of intramolecular bond lengths on the intermolecular interactions between H2 and AgCl molecules. Using four sets of bond lengths for the monomers of H2 and AgCl, four-dimensional intermolecular potential energy surfaces (PESs) were constructed from ab initio data points at the level of single and double excitation coupled cluster method with noniterative perturbation treatment of triple excitations. A T-shaped global minimum was found on the PES. Interestingly, both the binding energies and Ag–H2 distances present a linear relationship with the intramolecular bond lengths of H2–AgCl. The accuracy of these PESs was validated by the available spectroscopic data via the bound state calculations, and the predicted rotational transition frequencies can reproduce the experimental observations with a root-mean-squared error of 0.0003 cm−1 based on the PES constructed with r(H–H) and r(Ag–Cl) fixed at 0.795 and 2.261 Å, respectively. The intermolecular vibrational modes were assigned unambiguously with a simple pattern by analyzing the wave functions. Isotope effects were also investigated by the theoretical calculations, and the results are in excellent agreement with the available spectroscopic data. The transition frequencies for the isotopolog D2–AgCl are predicted with the accuracy of 0.3 MHz. [ABSTRACT FROM AUTHOR]

The properties of intramolecular hydrogen bond of a new photochemical sensor 4′- N, N-dimethylamino-3-hydroxyflavone ( dmahf) has been investigated in detail. Using Atoms-In-Molecule method, we have demonstrated that the intramolecular hydrogen bond was formed in the ground state (S state). The calculated dominating bond lengths and angles involved in hydrogen bond demonstrates that the intramolecular hydrogen bond can be strengthened in the first excited state (S state). In addition, the variation of hydrogen bond of dmahf has been also testified based on infrared vibrational spectra. Further, hydrogen bonding strengthening manifests the tendency of excited state intramolecular proton transfer process. According to the calculated results of potential energy curves along O-H coordinate, the potential energy barrier of about 7.49 kcal/mol is discovered in the S state. However, a lower potential energy barrier of 1.61 kcal/mol has been found in the S state, which demonstrates that the proton transfer process is more likely to happen in the S state than the S state. In other words, the proton transfer reaction can be facilitated based on the photoexcitation effectively. In turn, through the process of radiative transition, the proton-transfer form dmahf-keto regresses to the ground state with the fluorescence of 578 nm. [ABSTRACT FROM AUTHOR]

The intermolecular potential energy surfaces (PESs) of the ground electronic state for the Rg-BrCl (Rg = He, Ne, Ar, Kr, Xe) van der Waals complexes have been constructed by using the coupled-cluster method in combination with the augmented quadruple-zeta correlation-consistent basis sets supplemented with an additional set of bond functions. The features of the anisotropic PESs for these complexes are remarkably similar, which are characterized by three minima and two saddle points between them. The global minimum corresponds to a collinear Rg-Br-Cl configuration. Two local minima, correlate with an anti-linear Rg-Cl-Br geometry and a nearly T-shaped structure, can also be located on each PES. The quantum bound state calculations enable us to investigate intermolecular vibrational states and rotational energy levels of the complexes. The transition frequencies are predicted and are fitted to obtain their corresponding spectroscopic constants. In general, the periodic trends are observed for this complex family. Comparisons with available experimental data for the collinear isomer of Ar-BrCl demonstrate reliability of our theoretical predictions, and our results for the other two isomers of Ar-BrCl as well as for other members of the complex family are also anticipated to be trustable. Except for the collinear isomer of Ar-BrCl, the data presented in this paper would be beneficial to improve our knowledge for these experimentally unknown species. [ABSTRACT FROM AUTHOR]

A new three-dimensional potential energy surface (PES) of the Ne–N 2 van der Waals complex was constructed using the neural networks method based on ab initio data points at the CCSD(T) level. The aug-cc-pVQZ basis set was employed for all atoms, supplemented by midbond functions. The vibrationally averaged PES V 00 is characterized by a global T-shaped minimum which occurs at R = 3.385 Å, θ = 90.0° with a well depth of −49.202 cm −1 . Based on our three-dimensional PES, bound state calculations were performed for four isotopologues, i.e. 20 Ne– 14 N 2 , 22 Ne– 14 N 2 , 20 Ne– 15 N 2 , 22 Ne– 15 N 2 , and several intermolecular vibrational states were assigned by analyzing the wavefunctions. Moreover, the averaged structural parameters were determined and the pure rotational transition frequencies with J = 0–5 are predicted. The spectroscopic constants were 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 Ne–N 2 complex. [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]

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]

[Display omitted] • A semi-experimental PES was constructed at the level of CCSD(T)/aug-cc-pVTZ for the H 2 –CuF complex. • Pure rotational transition frequencies were well reproduced with the error of 0.1%. • A set of structural parameters were determined based on the rotational constants of six isotopologues. In this paper, a theoretical study has been made on the intermolecular interactions of the H 2 –CuF complex, including binding energy, intermolecular vibrations, isotope effects, and rotational structure. Based on different bond lengths of H 2 and CuF monomers, three intermolecular potential energy surfaces (PESs) were constructed at the level of single and double excitation coupled-cluster method with a non-iterative perturbation treatment of triple excitations [CCSD(T)] with aug-cc-pVTZ basis set supplemented with bond functions. A global minimum on the PESs show that H 2 –CuF complex belongs to C 2ν point group with a T-shaped structure. The obtained binding energy ranges from 8890 to 10050 cm−1, which increases as the increment of H–H bond length, but opposite case has been determined as the increment of Cu–F bond length. The accuracy of PESs was examined by the available data of 1 01 –0 00 transition. The predicted rotational transition frequency obtained from bound state calculations can reproduce the experimental observation very well, and the predicted error is 0.1% based on the PES1 constructed with r H2 and r CuF fixed at 0.838 and 1.7409 Å. By analyzing the wave function of the bound state, the intermolecular vibrational modes were assigned unambiguously. Isotope effects were also studied and the largest error is also 0.1% compared with the available 1 01 –0 00 transition data. A set of spectroscopic parameters were obtained for six isotopologues to determine rotational structure of H 2 –CuF complex. Upon the complex formation, the obtained structure parameters show that H–H bond length is elongated by 0.081 Å, while Cu–F value is shortened by 0.008 Å from the respective average bond lengths of free monomer. [ABSTRACT FROM AUTHOR]

Abstract: The rovibrational spectrum of the N2–N2O van der Waals complex has been recorded in the N2O ν 1 region (∼1285cm−1) using a tunable diode laser spectrometer to probe a pulsed supersonic slit jet. The observed transitions together with the data observed previously in the N2O ν 3 region are analyzed using a Watson S-reduced asymmetric rotor Hamiltonian. The rotational and centrifugal distortion constants for the ground and excited vibrational states are accurately determined. The band-origin of the spectrum is determined to be 1285.73964(14)cm−1. A restricted two-dimensional intermolecular potential energy surface for a planar structure of N2–N2O has been calculated at the CCSD(T) level of theory with the aug-cc-pVDZ basis sets and a set of mid-bond functions. With the intermolecular distance fixed at the ground state value R =3.6926Å, the potential has a global minimum with a well depth of 326.64cm−1 at =11.0° and =84.3° and has a saddle point with a barrier height of 204.61cm−1 at =97.4° and =92.2°, where is the enclosed angle between the N–N axis (N–N–O axis) and the intermolecular axis. [Copyright &y& Elsevier]

• An effective methodology is developed to predict the infrared spectra of van der Waals complexes and successfully applied to the complex Ar–CO. • The full-dimensional Hamiltonian of a complex can be strictly divided into three parts which are solved with higher accuracy and less computing resources. • The vibrational shifts are accurately predicted with the errors of 0.16% and 1.68% for two infrared bands. In this work, we developed an effective methodology to predict infrared spectra of van der Waals complexes and successfully applied it to the prototype system of Ar–CO complex. The basic idea is to divide strictly the full-dimensional Hamiltonian of a complex into three parts, named as rigid-rotor-approximation Hamiltonian, monomer Hamiltonian, and intramolecular and intermolecular coupling Hamiltonian, respectively. Following the three parts, intermolecular potential energy surfaces (IPESs) were firstly constructed at the rigid rotor approximation for ground and vibrationally excited states of Ar–CO complex. Then, potential curves were calculated for ground and vibrationally excited states of CO monomer with the intermolecular equilibrium structural parameters fixed. Based on these PESs, the bound state calculations were performed to obtain the rovibrational levels and average structural parameters. Finally, the intermolecular and intramolecular coupling Hamiltonian was calculated using the average structural parameters obtained from the previous steps. Our predicted vibrational shifts and spectroscopic parameters for Ar–CO complex are all in good agreement with available experimental data. The vibrational shift was calculated to be –0.4384 cm–1 for the fundamental and –0.8925 cm–1 for the overtone bands, which reproduce experimental results with the error of 0.16% (–0.4377 cm–1) and 1.68% (–0.8778 cm–1), respectively. In brief, the advantages of this methodology are its higher accuracy for predicting infrared spectra and are less computing resources for constructing IPESs than those of the full-dimensional quantum calculations. Image, graphical abstract [ABSTRACT FROM AUTHOR]

• A corrected four-dimensional potential energy surface was constructed for the H 2 -AgCl complex. • The full-dimensional structural parameters were accurately determined upon the H 2 -AgCl complex formation. • Intramolecular effects were investigated in detail concerning intermolecular vibrational frequencies and rotational transitions. • Pure rotational spectra were predicted for one parallel and two perpendicular bands. An efficient model was developed by optimizing the terms of intermolecular potential and monomer rotations in the Hamiltonian, and then was applied to determine the global structures and rotational transitions of H 2 –AgCl complex. Based on this model, a detailed study of intramolecular effects were examined for intermolecuar vibrational modes, rotational transition frequencies, and spectroscopic parameters relative to those of rigid-rotor-approximation model. Firstly, the full-dimensional equilibrium geometry is determined to be (R e , r 1e , r 2e , θ 1e , θ 2e , φ e) = (2.370 Å, 0.7785 Å, 2.2579 Å, 90.0°, 180.0°, 0.0°), and the averaged structure is determined to be (R ν , r 1 ν , r 2 ν , θ 1 ν , θ 2 ν , φ ν) = (2.436 Å, 0.7905 Å, 2.2604 Å, 76.4°, 172.8°, 0.0°), which are in excellent agree with the available data of experimental observations. In addition, the available transitions were accurately predicted with the maximal percentage error of 0.05%. Based on the determined spectroscopic parameters, two perpendicular bands were predicted and will be helpful to guide the further investigations in the far infrared spectral region experimentally. [Display omitted] [ABSTRACT FROM AUTHOR]

• An effective methodology (3H-solution model) was used to investigate the infrared spectrum of Ar–AgF complex as well as the full-dimensional model. • The calculated vibrational shifts were excellent agreement indicating the 3H-solution model (29.14 cm−1)and full-dimensional models (29.11 cm−1) were very high consistency. • By 3H-solution model, the contribution for vibrational shift of each term can clearly determined, including intermolecular interactions and intramolecular interactions and intermolecular-intramolecular coupling interactions, which model is promising for high-dimensional systems. In this work, we investigate the infrared spectrum of the Ar–AgF complex by using two methodologies. The first is performed by the computation of full-dimensional dynamics, and the second is obtained by solving the full-dimensional Hamiltonian separately. The vibrational shift, which shows excellent agreement with each other, is determined to be 29.11 cm–1 from the former methodology and 29.14 cm–1 from the latter methodology upon AgF excitation in the Ar–AgF complex. For the latter methodology, the contribution from intermolecular interactions is determined to be a positive value of 39.45 cm–1, while that from intramolecular interactions is only 0.51 cm–1, which is the difference of the intermolecular force acting on the AgF monomer. The contribution from intermolecular-intramolecular coupling interactions is determined to be a negative value of –10.82 cm–1. Since the full-dimensional Hamiltonian of the van der Waals dimer can be divided into three sub-units, the latter methodology is named the 3H-solution model. Based on the potential energy surfaces and bound state calculations, infrared spectra were predicted for the fundamental and the first two combination bands of the Ar–AgF complex. [Display omitted] [ABSTRACT FROM AUTHOR]

• The 2D-PESs of Ar–CuX are constructed. • Intermolecular vibrational states are assigned. • Transition frequencies and spectroscopic constants are accurately predicted. • The changes of Cu–F distance in Ar–CuF are determined based on the 3D-PES. New intermolecular potential energy surfaces (PESs) are constructed at the level of the non-iterative perturbation treatment of triple excitations [CCSD(T)] plus aug-cc-pVQZ basis set supplemented with bond functions for the complexes Ar–CuX (X = F, Cl, Br, and I) at the rigid rotor approximation. The global minimum is assigned to be a collinear Ar–Cu–X geometry, while the local minimum is an anti-linear Cu–X–Ar geometry on the PES for each complex. Based on the PESs, the intermolecular vibrations, pure rotational spectra, as well as isotope effects are investigated via the bound state calculations. We also give a detailed comparison of the structural parameters, binding energies, accuracy of PESs, as well as the results of basis set superposition error (BSSE) correction with those of Ar–AgX complexes. In addition, we construct a three-dimension (3D) intermolecular PES for the complex Ar–CuF, which not only gives the information of structural change for Cu―F distance upon the complex formation, but also reproduces the rotational spectroscopic characteristics much better. Image, graphical abstract [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • The PESs were constructed for the ground and excited states for Ar–N 2 O complex. • The infrared spectra of fundamental and combination bands can be accurately predicted. • The perturbation probably exists for the infrared spectrum of fundamental band in the N 2 O ν 1 region. Abstract In this work, we performed a theoretical study of fundamental and combination bands for the infrared spectra of the Ar–N 2 O complex based on high-precision potential energy surfaces and bound state calculations. We constructed three two-dimensional potential energy surfaces (PESs) for the ground and excited states of the Ar–N 2 O complex. The bound state calculations were performed to determine the energies of rotational and intermolecular vibrational levels for this complex. Based on the results of the bound state calculations, we provide predictions for the infrared spectra of the Ar–N 2 O complex, including the fundamental and combination bands in the ν 1 and ν 3 regions of the N 2 O monomer. The theoretical results are in excellent agreement with experimental data, so our predicted results could be helpful to further investigate the infrared spectrum of van der Waals complex Ar–N 2 O. [ABSTRACT FROM AUTHOR]

Two potential energy surfaces (PESs) were constructed for the ground and excited states of Ar–CO 2 complex at the rigid rotor approximation. Besides the notable T-shape structure, two equivalent linear structures were also found on the PES for the first time. Based on the PESs of ground and excited states, the bound state calculations were performed to determine the rotational energy levels for the ground and excited states. In combination of the experimental spectroscopic parameters of ground state and the differences of rotational energy levels, we give a theoretical prediction of infrared spectra including one fundamental band and two combination bands for two isotopomers Ar– 12 C 16 O 2 and Ar– 12 C 18 O 2 in the ν 3 region of CO 2 monomer. The predicted transition frequencies and spectroscopic parameters of excited states are in excellent agreement with the available experimental data, and these results can also be used as a guide to perform the further investigation for the infrared spectra of combination bands experimentally. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • Ab initio PESs were constructed for the complexes Ar–AgX. • The collinear and anti-lnear structures were determined for Ar–AgX. • Microwave spectra and spectroscopic constants were predicted for Ar–AgX. • Transition frequencies can be accurately predicted based on a scaled PES. Abstract Theoretical studies of the potential energy surfaces (PESs) and bound state calculations were performed for Ar–AgX (X = F, Cl, Br, and I) complexes. A two-dimensional intermolecular PES was constructed at the level of single and double excitation coupled-cluster method with a non-iterative perturbation treatment of triple excitations [CCSD(T)] plus aug-cc-pVQZ basis set supplemented with bond functions for each complex. The global minimum was assigned as the collinear structure of Ar–Ag–X, while the local minimum was assigned as the anti-linear structure of Ar–X–Ag. Both Ar–Ag and Ar–X distances display us an increasing trend from Ar–AgF to Ar–AgI complexes. Based on the bound state results, the intermolecular vibrational modes of collinear and anti-linear isomers were studied in detail via the wavefunction analysis. Due to the very low well depth for the anti-linear structure, an obvious delocalization effect was observed for each complex, except for Ar–AgI. Furthermore, our calculated results suggest that the anti-linear isomer of Ar–AgBr and Ar–AgI could be observed in experiment. The rotational energy levels were also determined based on the ab initio PESs via the bound state calculations. The microwave spectrum for the collinear isomer of each complex was predicted with the maximal percentage error of 1.55% for the complex Ar–AgF. A simple method of coordinate translation was used to re-interpolate the PES for each isotopomer to determine the isotope effects for Ar–AgX complexes and the deduced results are in good agreement with those of experimental observation. The microwave spectrum can be much better reproduced with an equivalent percentage error of 0.07% cm−1 for each isotopomer based on a scaled PES. Finally, we checked the effects of the basis set superposition error (BSSE) correction and core correlation, and found that the BSSE correction has great influence on the intermolecular interactions for the Ar–AgX complexes. [ABSTRACT FROM AUTHOR]

Intermolecular interactions, equilibrium parameters, intermolecular vibrational states and spectroscopic constants for the Rg-IBr (Rg = He, Ne, Ar, Kr, Xe) van der Waals complexes are studied theoretically. The equilibrium geometries of global minima for the complex family are characterized by the collinear Rg-I-Br configurations. The local minima of anti-linear Rg-Br-I and nearly T-shaped structures are also located on the potential energy surfaces. The intermolecular vibrational states, average structural parameters and spectroscopic constants for these complexes are determined for each conformer. Interpretations of the characters of the potential energy surfaces reveal the different extent of the anisotropic feature. The probability density distribution of intermolecular vibrational states indicates the quantum tunneling effect is much easier to occur for He- and Ne-IBr owing to their lower barrier height. As for Ar-, Kr- and Xe-IBr complexes, the localization effect enables us to investigate more intermolecular vibrational excited states. The predicted spectroscopic constants of all conformers for each complex are anticipated to fill our knowledge gaps of this complex family. [ABSTRACT FROM AUTHOR]

We constructed three potential energy surfaces (PESs) for the ground and excited states of each complex including He–CS 2 , Ne–CS 2 , and Ar–CS 2 , respectively. Based on these PESs, the bound state calculations were performed to determine the rotational levels of the ground and excited states. Combining the experimental spectroscopic parameters of ground state and the rotational level differences between the ground and excited states, we accurately predicted the infrared spectra in the ν 1 and ν 1 + ν 3 regions of CS 2 monomer. The determined spectroscopic parameters and transition frequencies are in excellent agreement with the available experimental data. [ABSTRACT FROM AUTHOR]

In this present work, adopting density functional theory (DFT) and time-dependent density functional theory (TDDFT) methods, we theoretically research the excited state dynamical process about two imide compound N-cyclohexyl-3-hydroxyphthalimide (3HNHPI) and 3,6-Dihydroxy-N-cyclohexylphthalimide (DHNHPI). We find the intramolecular hydrogen bonds in these two systems should be strengthening in the S 1 state, which may trigger excited state intramolecular proton transfer (ESIPT) reaction. Analysis about charge redistribution implies the tendency of ESIPT reaction for both 3HNHPI and DHNHPI. However the constructed potential energy surfaces confirm that the ESIPT process should occur for 3HNHPI rather than DHNHPI molecule, which is consistent with previous experiment [Phys. Chem. Chem. Phys. 17 (2015) 30659–30669]. Via transition state (TS) theory, we successfully account for the vague explanation in previous work and clarify that why the proton transfer reaction missing for DHNHPI in the S 1 state. [ABSTRACT FROM AUTHOR]

A section of infrared spectrum for Xe–N 2 O has been recorded in the N 2 O monomer ν 1 region, but just 5 rotational resolved lines cannot make an effective rovibrational analysis. To improve the analysis of our observed spectrum for Xe–N 2 O, a new method is developed based on the bound state calculations with three ab initio potential energy surfaces (PESs). The accuracy of this method is validated by the excellent agreement between theoretical and experimental results for 152 rovibrational transition frequencies with a root mean square deviation of 0.00075 cm −1 and spectroscopic parameters with the deviation less than 0.6 MHz in the N 2 O monomer ν 3 region. The rotational constants for the excited state are derived with the values of A = 12716.1, B = 1075.2, C = 987.9 MHz in the ν 1 region of N 2 O monomer. The band origin of the spectrum is determined to be 1284.8760 cm −1 with a red shift of 0.0273 cm −1 compared with that of N 2 O monomer in the ν 1 region. The excellent agreement between experimental and theoretical results confirms that this new method is extremely helpful to make a rovibrational analysis for the infrared spectrum of van der Waals complex. [ABSTRACT FROM AUTHOR]

[Display omitted] • An error-correction model has been developed to predict the microwave spectra efficiently. • Due to the intramolecular effects included, the predicted transition frequencies were well reproduced with the error of 0.017%. • the intermolecular modes of Ar–AgF complex can be well described by an analogous form of Dunham series. An error-correction model has been developed to predict pure rotational spectrum of Ar–AgF complex. Firstly, based on the geometry optimizations, bond length was determined for AgF of free monomer and in Ar–AgF complex, respectively. Then, a scaled bond length for AgF was obtained by introducing the value of free monomer observed experimentally. Subsequently, a two-dimensional intermolecular potential energy surface (PES) was constructed for Ar–AgF complex. Due to the intramolecular effects included and bond length corrected in the PES, this model could well reproduce transition frequencies with an error of 0.017% for the microwave spectrum of Ar–AgF complex. Furthermore, a full-dimensional PES was also constructed for comparison, and results of bound state calculations produced an error of 0.029%, suggesting that the error-correction model is reliable and efficient according to the excellent agreement between theoretical and experimental results from transition frequencies and spectroscopic parameters. [ABSTRACT FROM AUTHOR]

Theoretical studies of potential energy surfaces and bound states were performed for Kr/Xe–CS 2 complexes. The two intermolecular potential energy surfaces (PESs) for the Kr/Xe–CS 2 complexes were constructed from ab initio data points at the CCSD(T) level. The two PESs have similar features, characterized by a global T-shaped minimum and two equivalent local linear minima, along with the saddle points between them. Based on our ab initio PESs, bound state calculations were performed, and several intermolecular vibrational states were assigned unambiguously by analyzing the wavefunctions. The average structural parameters were determined, and the rotational frequencies for the transitions with J = 0–5 were predicted. The rotational constants ( A , B , and C ) were determined by fitting the energy levels to the Hamiltonian of an asymmetric top and were found to be reliable. The band origin shifts for Kr/Xe–CS 2 complexes were predicted based on the Buckingham potential. These calculated results could be useful in the experimental study of the microwave spectra of Kr/Xe–CS 2 complexes. [ABSTRACT FROM AUTHOR]

In this work, we have studied the isotope effects for the He–CO 2 and Ne–CO 2 complexes by means of theoretical calculations and experimental measurements, which were carried out using a distributed quantum cascade laser to probe a pulsed supersonic jet expansion. Firstly, infrared spectra have been recorded for the He/Ne–12C18O 2 complexes. Spectroscopic parameters including band origin ν 0 , rotational constants A , B , C , and centrifugal distortion constants Δ JK were obtained by fitting a Watson A -reduced Hamiltonian with 13 assigned rovibrational transitions for He–12C18O 2. For Ne–12C18O 2 , the observed spectrum produces a set of spectroscopic parameters including the band origin, rotational constants and all the quartic centrifugal distortion constants with more than 100 rovibrational transitions (40 new transitions). Secondly, we have calculated the rovibrational energy levels, vibrational shifts, and rotational constants for the He/Ne–CO 2 complexes based on potential energy surfaces (PESs) and bound state calculations for ground and vibrationally excited states. The obtained results show that the spectroscopic characteristics (vibrational shifts and rotational constants) for Ne–CO 2 are analogous to those of Ar–CO 2 , while those for He–CO 2 show some differences especially for the rotational constants. Finally, according to the available experimental data and our theoretical calculations, infrared spectra were predicted for six isotopologues with C 2 v symmetry of Ne–CO 2 complex. [ABSTRACT FROM AUTHOR]

In this work we report an ab initio intermolecular potential energy surface and theoretically spectroscopic studies for N 2 –OCS complex. A four-dimensional intermolecular potential energy surface (4D PES) is constructed at the level of single and double excitation coupled-cluster method with a non-iterative perturbation treatment of triple excitations [CCSD(T)] with aug-cc-pVTZ basis set supplemented with bond functions. A global minimum corresponding to a planar and nearly T-shaped structure, which has been observed experimentally, is located at R = 3.96 Å, θ 1 = 8 or 172°, θ 2 = 75°, φ = 180 or 0° with a well depth of 271.078 cm−1 on the potential energy surface. The local minimum corresponding to a linear geometry is also found at R = 5.06 Å, θ 1 = 2 or 178°, θ 2 = 179°, φ = 0 or 180° with a well depth of 224.743 cm−1. The bound state calculations have been performed for the complex by approximating the N 2 and OCS molecules as the rigid rotors. The calculated structural parameters and rotational transition frequencies are in good agreement with the experimental observed values. Based on the ab initio PES, the tunneling splitting is calculated to be 0.052 cm−1 for the ground vibrational state, which can just reproduce 64% of experimental observation (0.082 cm−1). A refined method is used to calculate the tunneling splitting, and a much better result is obtained with the value of 0.094 cm−1. Unlabelled Image • Two symmetrically equivalent nearly T-shaped and linear minima are found on the PES. • The tunneling splitting for the vibrational ground state are calculated to be 0.094 cm−1. • The average structures and rotational constants are predicted for both nearly T-shaped and linear isomers. [ABSTRACT FROM AUTHOR]

• The vibrational shifts and rotational constants display a linear relationship for the isotopologues of Ar–CO 2 complex. • The linear relationship is classified into two types according to 12C and 13C in the CO 2 monomer. • The infrared spectra are accurately predicted for ten isotopologues of Ar–CO 2 complex. In this paper, we perform a theoretical study of isotope effects for the Ar–CO 2 complex. Based on the two-dimensional potential energy surfaces (PESs) for the ground and vibrational excited state, the rotational energy levels are obtained for twelve isotopologues of the Ar–CO 2 complex via bound state calculations. Our predicted vibrational shifts and rotational constants display two interesting characteristics for these twelve isotopologues. Firstly, the vibrational shifts and rotational constants for these isotopologues are determined to be a linear relationship, which is in good agreement with the available experimental results. Furthermore, the linear relationship for the vibrational shifts and rotational constants can be classified into two types according to the 12C and 13C in the CO 2 monomer. Then the vibrational shifts of the remaining nine isotopologues unobserved experimentally are deduced based on our theoretical predictions and available experimental data. Finally, the infrared spectra of ten isotopologues for the Ar–CO 2 complex are accurately predicted. Image, graphical abstract [ABSTRACT FROM AUTHOR]

This study is a continuation of our previously published research for the N 2 –N 2 O complex [Journal of Chemical Physics 143 (2015) 154304], and focuses on predicting the quantum tunneling effects of infrared fundamental and combination bands. A new four-dimensional intermolecular potential energy surface (PES) was constructed for the vibrational excited state upon the N 2 O ν 1 excitation at the same calculated level with the previous PES of ground state. Compared with the ground state, two equivalent T-shaped global minima are found to be slightly different in both structural parameters and binding energies. Based on the PESs of ground and vibrational excited states, the vibrational shift of infrared spectrum for the fundamental band in the N 2 O ν 1 region is determined to be a blue shift of 1.29 cm−1 for 14N 2 –N 2 O, which is in qualitative agreement with the experimentally observed value of 2.233 cm−1 [Journal of Chemical Physics 140 (2014) 044332]. Furthermore, for the fundamental and disrotation bands, the calculated tunneling splitting is almost the same for the ground and vibrational excited states, so the tunneling effects cannot be observed for these bands using the infrared spectroscopic technique. Nevertheless for the infrared combination bands, our calculated results suggest that the tunneling effects for the torsion and twice disrotation bands are significantly larger, and the predicted infrared spectra display obvious differences for the different sub-states. If the sensitivity of infrared spectrometer is high enough, it is interesting to investigate the quantum tunneling effects experimentally. Unlabelled Image • The vibrational shift of infrared spectra was predicted to be blue-shift for N 2 –N 2 O complex upon the N 2 O ν 1 excitation. • The tunneling splittings increase as a function of the intermolecular vibrational frequencies. • The predicted infrared spectra for combination bands are obviously different for two tunneling sub-bands. [ABSTRACT FROM AUTHOR]