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Supercritical water has attracted much attention from both fundamental and technological perspectives, based largely on its ability to solvate other molecules. Predicting and controlling this requires a deeper understanding of water's polarisation behaviour. Using the computationally efficient Self-Consistent Electrostatic Embedding method, we were able to calculate the water dipole moment over an unprecedented range of thermodynamic conditions, covering gas, liquid and supercritical states, with large simulation systems and a high-level quantum mechanical method. We find a discontinuous change in the dipole moment along subcritical isotherms, corresponding to the sharp transition between the vapour and liquid states, with the latter exhibiting induced dipole moments between 0.5 and 0.9 D, depending on the temperature. In contrast, the dipole moment changes continuously from gas-like to liquid-like behaviour in the supercritical regime, allowing the degree of polarisation to be controlled through manipulating temperature and pressure. The dipole moment was found to be linearly related to the average number of hydrogen-bonded neighbours of water, emphasising the key role of local interactions to the polarisation process. Mean-field approaches based on a dielectric continuum representation of the solvent are unable to predict this behaviour due to the neglect of local interactions. [ABSTRACT FROM AUTHOR]

We have performed ab-initio calculations to investigate the van der Waals interaction between a Mg+ ion and a helium atom. We have focussed on determining the first low-lying electronic states of the Mg+–He ionic system using advanced theoretical methods, including RCCSD(T) and SA-CASSCF/MRCI, with the incorporation of Davidson and BSSE corrections. Furthermore, we have considered the influence of spin-orbit coupling SO on these states using the state-interacting method. Spectroscopic parameters of the potential energy curves PECs were calculated and compared with existing data from previous studies. Additionally, we have evaluated vibrational levels, their spacing, radiative lifetimes, transition dipole moments TDMs and permanent electric dipole moments PDMs. The position of satellites in the absorption spectra of white dwarfs was determined. Our results were compared with available theoretical and experimental data to assess their accuracy and agreement. This study provides valuable insights into the van der Waals interaction and electronic properties of the Mg+–He ionic molecule. [ABSTRACT FROM AUTHOR]

Lead is heavily utilised in industry, but it bears potential harm due to its toxic nature. Identifying lead is important in diagnosing and preventing lead poisoning. Hydride generation via inductively-coupled plasma mass spectrometer (HG-ICP-MS) can detect small amounts of lead with high accuracy. Here we investigate seven structures of Pb $ _2 $ 2 H $ _2^+ $ 2 + . The geometries of each structure were optimised using coupled cluster with single, double, and perturbative triple excitations [CCSD(T)] method with the cc-pwCVQZ-PP basis set for lead and the cc-pVQZ basis set for hydrogen. Likewise, harmonic vibrational frequencies were obtained using the same method. Anharmonic frequencies were determined using CCSD(T) with cc-pwCVTZ-PP and cc-pVTZ basis sets for lead and hydrogen, respectively. The focal point approach (FPA), including CCSDT and CCSDT(Q) computations, was applied to the seven structures to find the relative energies with respect to the global minimum butterfly structure. Relative to the global minimum butterfly structure, the energies for the planar transition state, monobridged, vinylidene-like, trans, cis, and linear structures are: 1.1, 18.3, 26.5, 27.8, 28.8, and 93.7 kcal mol $ ^{-1} $ − 1 , respectively. Natural bond orders and dipole moments are reported as well. The predicted vibrational frequencies should be helpful in guiding the laboratory observation of Pb $ _2 $ 2 H $ _2^+ $ 2 + . [ABSTRACT FROM AUTHOR]

A semiempirical molecular-orbital approach has been developed to calculate the dissociation energies of 57 second-row neutral and charged diatomic molecules. One-electron energies and wave functions were used. The 2s and 2p electrons have separate energies and separate values of Z2S and Z2P. Calculations were made with a CNDO/INDO FORTRAN programme modified to a level of approximation that is more similar to extended Hückel calculations than to either CNDO or INDO. The correlation between calculated and experimental dissociation energies was favourable with a relative standard deviation of 15%. Additionally, dipole moments for the molecules were calculated concurrently with the same parameters. The correlation between calculated and experimental dipole moments was favourable for seventeen molecules with a relative standard deviation of 19%. The correlation between calculated and experimental ionisation potentials for fourteen molecules was also favourable with a relative standard deviation of 11%. Also, a repulsion work function was formulated and used in this work between pairs of atoms. For 90% of the molecules studied, the maximum calculated dissociation energy occurred within ±0.1 Å of the experimental bond distance. The semiempirical methods used in the present work could be used for future studies of larger molecules, including organic molecules. [ABSTRACT FROM AUTHOR]

Density functional theory (DFT)-based calculations were performed for 36, 72 and 108 water molecules forming twisted ribbon-like nano-ring structures of diameter 1.54, 3.10 and 4.56 nm, respectively. We explore the electric field evolution of the structure, energetics and stability of the water nano-ring structures that are essentially symmetric and non-polar, or less-symmetric and polar, hydrogen-bonded clusters. The results suggest that for fields applied perpendicular to the ring, larger rings are more susceptible to the field influence, while fields applied parallel to the ring quickly transform the ring structures into arbitrary ones, regardless of the ring size. Infrared and Raman spectral analysis of local modes demonstrate the typical vibrational response of water molecules to various H-bonding environments and applied fields, providing a spectroscopic signature that can be used to identify the manifestation of such H-bonded ring networks. Our study underscores the implications of the nano-sized ring water clusters, which have the potential to be exploited in a variety of device applications. [ABSTRACT FROM AUTHOR]

To facilitate the data analysis of current and future high-resolution space telescope missions, we adopt 'Best Theory + Reliable High-resolution Experiment' (BTRHE) strategy to develop highly accurate infrared line lists for nitrous oxide (N2O). The 'Ames-1' potential energy surface (PES) is a CCSD(T)/aug-cc-pVQZ PES refined using selected HITRAN experimental data, with σrms = 0.02–0.03 cm-1 for five isotopologues. The 'Ames-1' dipole moment surface (DMS) is fitted from CCSD(T)/aug-cc-pV(T,Q,5)Z dipoles extrapolated to one electron basis set limit. Using the Ames-1 PES and DMS, Ames-296K line lists are computed in the full range of 0–15,000 cm-1 for 12 N2O isotopologues, with S296K ≥ 10−31 cm-1/molecule.cm-2. The reliability and consistency of Ames-296K intensity predictions (SAmes) are demonstrated through comparisons with HITRAN (SHITRAN), NOSL-296 (SNOSL), recent observed intensities (Sobs) and Effective Dipole Model (EDM) intensities (SEDM). Agreements and discrepancies are discussed, along with preliminary uncertainty estimate for SAmes. The SAmes provides a good constraint to prevent substantial errors in intensity predictions (e.g. for weak bands and minor isotopologues) and can be further improved. Ames-296K and NOSL-296 may complement each other to provide improved input for future database updates, combining the strengths of EH/EDM and BTRHE approaches. Data available at and https://doi.org/10.48667/9kmk-0334. [ABSTRACT FROM AUTHOR]

This study deals with the broadening of atomic sodium, evolving in a neon buffer gas, in the wavelength and temperature ranges $ 500{\rm --}700\, {\rm nm} $ 500 − − 700 nm and $ 136{\rm --}3000\, {\rm K} $ 136 − − 3000 K , respectively. The computed emission and absorption spectral profiles are based on the most recent potential energy curves and transition dipole moments. The required electronic $ \mathrm {Na} (^{2}S) $ Na (2 S) $ +\mathrm {Ne}(^{1}S) $ + Ne (1 S) and $ \mathrm {Na}(^{2}P)+\mathrm {Ne}(^{1}S) $ Na (2 P) + Ne (1 S) potentials are used from two different sets. Then the satellite structures in the blue wing are analysed quantum mechanically. The calculations show especially that the free–free transitions contribute most to the NaNe photoabsorption spectra and a satellite structure is observable beyond the temperature $ 402\, {\rm K} $ 402 K around the wavelengths $ 550\, {\rm nm} $ 550 nm depending on the used potential set. The obtained results showed good agreement with those already published. [ABSTRACT FROM AUTHOR]

By using CCSD(T) and EOM-CCSD methods together with quasirelativistic energy-consistent small-core pseudopotentials and large atom-centered basis sets as well as bond functions, the potential energy curves (PECs) for the ground state and several low-lying singlet excited states of the van der Waals molecular systems between cadmium atom interacting with RG atoms (RG = He, Ne, Ar, Kr, Xe and Rn) are obtained. The dispersion coefficients of ground state for Cd-RG have been computed. And the spectroscopic constants of the bound states of Cd-RG molecules have been calculated, the spectroscopic constants of ground state and C1Π state of Cd-RG complexes are in reasonable agreement with the available theoretical and experimental results; the vertical excitation energies of singlet low-lying excited states are also obtained. And the transition dipole moments (TDMs) of (3)1Σ+-X1Σ+ and (4)1Σ+-X1Σ+ transitions are discussed, which would be helpful to understand the transition properties of Cd-RG complex. Furthermore, frequencies of vibrational transitions, rotational constants, Franck-Condon factors (FCFs) of C1Π-X1Σ+ transition and oscillator strengths of Cd-RG have also been acquired. The present work would be of value to understand on the electronically excited states of Cd-RG molecule, especially the electronic structure and spectroscopic characteristics of the singlet excited states. [ABSTRACT FROM AUTHOR]

The combined use of the MRCI-SD(T) method with the cc-pV6Z basis set has enabled us to determine the potential energy curves of the molecular cation CH + whose fundamental X 1 Σ + state lies 111.12 nm above the corresponding X 2 Π state of its neutral parent CH at the dissociation limit. With the accurate potential energy curves thus obtained, we have calculated spectroscopic constants which show good agreement with the experimental and other theoretical values available in the literature. To account for perturbations where necessary, spin-orbit coupling effects have been introduced. An understanding of the polarity of CH + studied in the various electronic states is made possible by calculating the dipole moments. In addition, transition dipole moments were computed prior to the obtention of molecular parameters such as oscillator strength, Einstein coefficients, radiative probabilities and Franck–Condon factors. Overall good accuracy is observed. [ABSTRACT FROM AUTHOR]

A promising laser cooling candidate molecule is essential for laser cooling experiments. In this study, the possibility of laser cooling an 88Sr35Cl molecule is investigated using an ab initio method. Seven low-lying Λ-S and six Ω electronic states of the 88Sr35Cl molecule are calculated at a multi-reference configuration interaction level of theory. Spectral constants of bound states of fitted values are in good agreement with experimental values, which are better than the previously obtained theoretical data for higher excitation states. The resulting permanent and transition dipole moments near the equilibrium bond length are close to the theoretical values. Potential energy curves and transition dipole moments are used for obtaining highly diagonally distributed Franck-Condon factors for the A2Π → X2Σ+ transition using the LEVEL program. A short radiative lifetime of the A2Π state is determined; a laser cooling scheme is designed in the vibration level that requires a cooling main laser beam and two repumping laser beams. Transition spectral data of hyperfine energy levels with errors relative to the experimental data do not exceed −0.25∼0.19 MHz when using a quantum effective Hamiltonian approach. This study provides a helpful reference for experimental observation and operation of laser cooling the 88Sr35Cl molecule. [ABSTRACT FROM AUTHOR]

For engineering applications, one of the most important characteristics of fluid mixtures is the vapour–liquid equilibrium (VLE). Knowledge of the VLE of mixtures containing simple model components like Lennard-Jones (LJ) and Stockmayer (ST) fluids can offer insight into how different modes of molecular interaction shape the phase behaviour of mixtures. However, studies investigating such mixtures are still scarce in the literature, especially for mixtures with an LJ fluid as the high boiling substance. In this work, the VLE of mixtures consisting of LJ and ST fluids are studied with molecular simulation using the Grand Equilibrium method. The energy parameter and length parameter of the LJ fluids and the dipole moments of the ST fluids are varied systematically to generate different types of mixtures. These mixtures are investigated within a broad temperature range. VLE envelopes and molarities are reported as well as additional data on the bubble and dew line including enthalpies, chemical potentials, and activity coefficients. These data fill a gap in the literature by furthering the understanding of how polarity affects phase behaviour in mixtures and are therefore of critical importance, e.g. for the development of theoretical approaches for the description and prediction of phase behaviour for polar mixtures. [ABSTRACT FROM AUTHOR]

Laser measurements of the intensity of (201) 3 22 − (000) 2 21 near-infrared water absorption line at 10,670.1 cm − 1 are made using three different Herriott cells. These measurements determine the line intensity with an standard deviation below of 0.3% by consideration of the new geometrically derived formula for the optical path length without approximations. This determination together with the current accepted value lead to an overall uncertainty of 0.7% of the experimentally assessed line intensity which is compared with previous ab initio predictions. It is found that steady improvements in both the dipole moment surface (DMS) and the potential energy surface (PES) used in the theoretical studies lead to a systematically better agreement with the observation, with the most recent prediction agreeing closely with the experiment. [ABSTRACT FROM AUTHOR]

Correlations among Shimura's parameter (dCo) from spectrochemical series for 34 ligands and electronic descriptors from density functional theory calculations are reported. Simple and multiple linear regression models were constructed. The best results were obtained with the descriptors estimated with MN15 functional, obtaining a multiple linear regression model based on a quantitative structure–property relationship (QSPR) approach, with four attributes and the statistical parameters: R2 = 0.8543, Q2LOO = 0.8050, and Q2LMO = 0.7977. The four molecular descriptors are ligand field splitting (Δ), dipole moment (χC), enthalpy of the metal complex (HC) and the ligand HOMO energy (EHO_L). This model obtained for the Ni(0) complexes represents a novel approach to the spectroscopic series description based on computational tools also revising the models proposed from Werner's description until modern recompilations carried out across the spectroscopic series developments. The applicability of the model was evaluated on cooper complexes and good prediction of the dCo values for some ligands was also obtained. [ABSTRACT FROM AUTHOR]

An organic salt compound 4-amino-3,5-dimethyl-1H-pyrazole (ADMP) has been combined with citric acid and crystallised at room temperature, forming a new molecular salt 4-amino-3,5-dimethyl-1H-pyrazolium citrate (ADMPCA) as a monohydrate. The compound was then structurally characterised by single-crystal X-ray diffraction (XRD), spectral analysis of FTIR, NMR and UV, and thermal studies. The structural analysis has shown that the ADMP molecules participate in the dominant hydrogen-bonding patterns forming a ladder-like structure via charge-assisted N+–H···O, O–H···O and N–H···O hydrogen bonds. The Hirshfeld surface analysis has been performed to understand the importance of intermolecular interactions in the stability of the salt structure. Theoretical studies were performed employing the DFT/B3LYP/6-311++G(d,p) level of theory to investigate Non-linear optical (NLO) behaviour, first-order hyperpolarisability, dipole moment and polarisability. The molecular properties, such as natural charge analysis and MESP analysis, were also explored in the present study. [ABSTRACT FROM AUTHOR]

We study the surface interaction of C60 with superalkali (SA) clusters for SA = FLi2, OLi3 and NLi4 using a density functional approach and compare it with exohedral LiC60 complex. The interaction takes place via two or more Li–C bonds and leads to SAC60 complexes, which are stabilised by electron transfer from SA to C60 moieties. Thus, SAC60 complexes can be represented as (SA)+C60− having enhanced dipole moment and the energy gap, unlike endohedral SA@C60 complexes with negligible dipole moment and lower energy gap. These findings suggest that C60 fullerene can be activated by the surface interaction with SA clusters. [ABSTRACT FROM AUTHOR]

Some models were developed for the interpretation of infrared intensities based on the distribution of molecular charge and its mobility during atomic displacement. The objective of this paper is to apply NPA charges in the C-CF-O model to obtain the dipole moment derivatives and infrared intensities of AH3, X2CY and some linear molecules. In all cases analyzed, the NC-NCF-O model was more accurate than the reference model Charge – Charge Flux – Dipole Flux (C–CF–DF). Furthermore, the computational cost of obtaining NPA charges and their respective flux are much lower than those obtained by more complex models. This allows a greater application for large molecules. [ABSTRACT FROM AUTHOR]

The thermodynamic and radiative properties of TiO in the local thermodynamic equilibrium (LTE) and non-LTE (NLTE) were investigated. Firstly, we investigated the potential energy curves of fifteen electronic states of TiO by the icMRCI + Q method with a large aug-cc-pwCV5Z-DK basis set. Then the internal partition functions, average internal energies, specific heats at temperatures from 100 to 15,000 K in the LTE and NLTE were obtained. The contributions of different states are not affected by the condition of the gas. In addition, the transition dipole moments for eight transitions and the radiative properties (absorption and emissivity) of TiO in the LTE and NLTE were obtained. The A3Φ−X3Δ, B3Π−X3Δ and C3Δ−X3Δ transitions play a key role in the calculations of the absorption and emissivity. The absorption and emissivity in the LTE and NLTE were also calculated, and the electronic and vibrational energy highly contributes to the absorption and the translational and rotational energy highly contributes to the emissivity. [ABSTRACT FROM AUTHOR]

In this paper, the formalism describing the spontaneous emission rate of an excited molecule (or atom) with definite transition electric dipole moment, in vicinity of a perfect conductive wall is developed. Separately, for molecules (or atoms) with the electric dipole moment parallel and perpendicular to the wall, the spontaneous emission rate of the molecule is calculated in two ways: (1) by using the explicit form of the vector potential operator in the Fermi' golden rule and taking the expectation value in vacuum state and (2) by considering the relation between the spontaneous emission rate and the vector potential Green function, and calculating the required Green function components of the space at the presence of a perfect conductive wall. The two methods yield the same expression for the spontaneous emission rate. The agreement of the results with some previous works is shown and the variations of the spontaneous emission rate for each dipole moment orientation are demonstrated. [ABSTRACT FROM AUTHOR]

We describe a novel variant of the driven molecular dynamics (DMD) method derived for probing Raman active vibrations. The method is an extension of the conventional μ-DMD formulation for simulating IR activity by means of coupling an oscillating electric field to the molecule's dipole moment, μ, and inducing absorption of energy via tuning the field to a resonant frequency. Presently, we modify the above prescription to invoke Raman activity by coupling two electric fields, i.e. a 'Pump' photon of frequency ωP and a Stokes photon of frequency ωS to the molecule's polarizability tensor, α, with the difference in the frequencies ω = ωP – ωS corresponding to the Stokes Raman shift. If ω is close to a Raman active vibrational frequency, energy absorption ensues. Varying ω allows identifying and assigning all Raman active vibrational modes, including anharmonic corrections, by means of trajectory analysis. We show that only one element of the full polarizability tensor, and its nuclear derivative, is needed for an α-DMD trajectory, making this method well suited for ab initio dynamics implementation. Numerical results using first-principles calculations are presented and discussed for the vibrational fundamentals, combination bands, overtones of H2O, CH4, and the C20 fullerene. [ABSTRACT FROM AUTHOR]

We describe a novel variant of the driven molecular dynamics (DMD) method derived for probing Raman active vibrations. The method is an extension of the conventional μ-DMD formulation for simulating IR activity by means of coupling an oscillating electric field to the molecule's dipole moment, μ, and inducing absorption of energy via tuning the field to a resonant frequency. Presently, we modify the above prescription to invoke Raman activity by coupling two electric fields, i.e. a 'Pump' photon of frequency ωP and a Stokes photon of frequency ωS to the molecule's polarizability tensor, α, with the difference in the frequencies ω = ωP – ωS corresponding to the Stokes Raman shift. If ω is close to a Raman active vibrational frequency, energy absorption ensues. Varying ω allows identifying and assigning all Raman active vibrational modes, including anharmonic corrections, by means of trajectory analysis. We show that only one element of the full polarizability tensor, and its nuclear derivative, is needed for an α-DMD trajectory, making this method well suited for ab initio dynamics implementation. Numerical results using first-principles calculations are presented and discussed for the vibrational fundamentals, combination bands, overtones of H2O, CH4, and the C20 fullerene. [ABSTRACT FROM AUTHOR]

In the present work, DFT calculations were carried out to investigate the electronic and structural properties of two six-membered 7-rings (A) and 19-rings (B) Li-decorated silicon carbide nanosheets (Li1-3-SiCNSs) at M06-2X/6-31+G(d) and B3LYP/6-31+G(d) levels of theory. The binding energies for pristine SiCNSs, adsorption energies for Li1-3-decorated SiCNSs, bond gap energies, the density of states (DOS), dipole moment, charge transfer values and global reactivity descriptors were explored. The results show that complexes containing two neighbouring Li atoms (A1,7 and B1,7) are more stable than other ones. The three Li atoms in cluster A tend to form the Li-Li bond, while in cluster B they tend to be apart from each other. The positive potential Vcell values (1.67 V for A1 and 1.96 V for B1) reveal that the Li@SiC → Li+@SiC oxidation process can be energetically a favourable half-reaction. This makes that the SiCNSs be a promising candidate for use as the anode material in the Lithium-Ion Batteries. DOS graphs show that Li1-SiCNS and Li3-SiCNS are magnetic materials with different spin polarisation properties. The total magnetic moment of Li1- and Li3-decorated SiCNSs is predicted to be 1.0 μB. [ABSTRACT FROM AUTHOR]

Low-lying electronic terms of 24 heteronuclear diatomic molecules AB (A = Sc–Ni, B = Cu/Ag/Au) have been systematically studied. Scalar relativistic effects were included by use of the spin-free Douglas–Kroll–Hess (DKH) Hamiltonian. The complete active space self-consistent field (CASSCF) method, followed by multi-reference configuration interaction (MRCI), was used to construct full potential energy curves (PECs). Spectroscopic constants as well as dipole moments are also reported. Spin-orbit coupling was subsequently calculated perturbatively via the spin-orbit terms of the Breit–Pauli Hamiltonian based on the CASSCF wavefunctions. Full spin-orbit coupled PECs were thus constructed for the low-lying terms of NiCu and NiAg. In addition, Kramers-restricted configuration interaction (KRCI) with the exact 2-component (X2C) Hamiltonian was utilised for the atoms and for the Cu-containing diatomic molecules. The influence of relativistic effects, spin-orbit coupling, core correlation effects and basis set incompleteness was probed for some selected cases. It is shown that for 23 out of the 24 diatomic molecules considered here a direct correspondence exists between the ground state terms (GSTs) of the monocations A + ((3 d 4 s) m − 1 2 S + 1 L J , m = 3 (S c) − 10 (N i)) and those of the diatomic molecules A B ((σ σ σ π δ) m + 1 X 2 S ′ + 1 Λ Ω) with S ′ = S , Λ = L and Ω = J. [ABSTRACT FROM AUTHOR]

The electronic, linear and nonlinear optical properties of some heterocycle-containing imino-dyes, namely, the synthesised dyes 1–3 and the designed dye 4, were evaluated using suitable long-range corrected DFT functionals. HOMO–LUMO gaps, dipole moments, polarisabilities, and first hyperpolarisabilities were calculated using CAM-B3LYP, ωB97XD and LC-ωPBE methods combined with the 6-311++G(d,p) basis set using CAM-B3LYP/6-31G(d,p) optimised geometries. The calculated molecular hyperpolarisabilities, µβ, increase in the order 1 < 2 < 3 as expected experimentally. The enhancement of µβ when passing from dye 1 to dye 2 is due to the replacement of furan by thiophene and the increase of µβ when passing from dye 2 to dye 3 is due to the change of the thiophene position from the acceptor side to the donor side. Interestingly, the replacement of thiophene (dye 2) by thiazole (dye 4) leads to a notable increase of the NLO response. The electronic transitions data of dyes 1–4 were calculated at the CIS/6-31G(d,p) level of theory and the predicted order 1 < 2<3 < 4 of µβ values is conveniently explained using the two-level model based on the calculation of the dipole moment absolute change, |ΔµEG|, from the ground to the excited state. Consequently, dye 4 could be a promising candidate for organic NLO devices. [ABSTRACT FROM AUTHOR]

Carbon monosulfide was detected in outer space by rovibrational spectroscopy of the X 1Σ+ state and A 1Π – X 1Σ+ system. This work calculated the potential energy curves and dipole moment functions of the X 1Σ+0+ and A 1Π1 states, and computed the transition dipole moments between the two states employing the CASSCF method, followed by the valence icMRCI approach. Core-valence correlation and scalar relativistic corrections were included. The extrapolation of potential energies to the complete basis set limit was performed. The spin-orbit coupling effect was included. The Einstein A coefficients, band origins, and oscillator strengths were calculated for the rovibrational transitions when J ≤ 150. The rovibrational transitions of the X 1Σ+0+ and A 1Π1 states became very weak when Δυ ≥ 6. The Einstein A coefficients of vibronic emissions of the A 1Π1 – X 1Σ+0+ system were large, indicating that the emissions were able to be measured easily through spectroscopy. Several rovibrational transitions of the A 1Π1 – X 1Σ+0+ system were analysed in detail. The distribution of radiative lifetime varying as rotational quantum number was calculated. The results obtained in this work agree well with the available experimental values. [ABSTRACT FROM AUTHOR]

The vertical excitation energies to the S 1 and T 1 states for HFCO were determined using multi-reference (CASSCF, CASPT2, CASPT2-F12, MRCI, and MRCI-F12) and the single reference EOM-CCSD methods. The geometries, relative energies, and harmonic frequencies for the stationary points (minimum and transition state to inversion) on both the S 1 and T 1 potential energy surfaces (PESs) were characterised. A six-dimensional PES for the S 1 state was constructed, in sum-of-products form using a neural network with exponential neurons, based on EOM-CCSD/aug-cc-pVTZ ab initio energies. Using the PES, the fundamental vibrational frequencies were computed using block-improved relaxation in MCTDH, and they agreed well with previous experiments (RMSE = 45 cm − 1 ). A corresponding transition dipole moment surface (TDMS) was also fit to sum-of-products form. With the present PES and TDMS, along with the previous S 0 surface, UV-vis absorption, stimulated emission pumping spectra, or optimal control of quantum dynamics via S 1 can be explored. [ABSTRACT FROM AUTHOR]

An algebraic approach based on the unitary U (4) algebra is proposed to describe 3D systems for effective potentials. Our approach is based on the 3D vibron model where the addition of a scalar boson is introduced into the space of a 3D harmonic oscillator. Our approach is based on the mapping between the U (3) dynamical symmetry and the harmonic oscillator states. A minimisation procedure is used in order to determine the coefficients involved in the algebraic expansions. This allows the kets associated with the different subgroup chains to be linked to energy, coordinate and momentum representations. As an application of this approach the eigensystem of the 3D-Morse potential is analysed in detail. The analyses of inertia moments as well as the dipole moment strengths are also included. To show the convenience of this approach, a comparison with one ab-initio calculation for vibrational and rotational levels for O 2 is presented in the framework of an analytical potential. In addition, a notch test is done to show how the formalism allows to check the sensitivity of the ro-vibrational results as a function of the precise structure of the potential energy surface as a function of r. [ABSTRACT FROM AUTHOR]

We study the structural, energetic and electronic properties of the structured water chain clusters within the density functional theory. We refer the structured water chains to those water clusters that have specific geometric patterns stretched along one direction. External electric field required to keep the structures open chain, thereby preventing them to form closed structures, is applied along the length of the chain. The structures are essentially periodic with basic repeating unit consisting of the corner- or edge-sharing 4-, 5- or 6-membered ring water clusters. Our calculations underscore the possible existence of such structured water clusters in the electrostatic environments, which we simulate in its simplicity employing a dipolar, uniform and static electric field. Analysis reveals that the 5-membered ring water chain clusters, i.e. the pentamer chain clusters have the lowest average dipole moment per water molecule while the threshold field, that marks the onset of the field-induced closure of the HOMO (highest occupied molecular orbital)-LUMO (lowest unoccupied molecular orbital) energy gap, is highest, followed by that for the tetramer and hexamer chains. The results suggest that the pentamer chains are the most stable clusters over a wide range of electric fields. [ABSTRACT FROM AUTHOR]

The high-resolution infrared spectrum of CHD279Br has been investigated by Fourier transform spectroscopy in the range 700–900 cm−1 at an unapodized resolution of 0.0035 cm−1. This spectral region is characterised by the absorptions of the ν5 (814.5185 cm−1) and ν9 (716.9649 cm−1) fundamental bands, corresponding to H–C–Br deformation and CD2 rocking modes, respectively. The ν5 vibration of symmetry species A′ gives rise to an a-/c-hybrid band with a predominant a-type component, while the ν9 mode of A′′ symmetry produces a b-type envelope. The spectral analysis resulted in the identification of 5290 (J′ ≤ 63 and Ka′ ≤ 13) and 1657 (J′ ≤ 53 and Ka′ ≤ 12) transitions for ν5 and ν9 bands, respectively. The assigned data were fitted using the Watson's S-reduced Hamiltonian in the Ir representation and the v5 = 1 and v9 = 1 state parameters up to the quartic centrifugal distortion terms have been obtained. From spectral simulations the dipole moment ratio |Δμa/Δμc| of the ν5 band has been determined to be 1.4 ± 0.1 while the intensity ratio between ν5 and ν9 fundamentals has been estimated to have a value of 4.3 ± 0.5. [ABSTRACT FROM AUTHOR]

The molecular structures, linear and nonlinear optical properties of a series constituted by four R-substituted thiophene imino dyes, namely A(R = SO2Me), B(R = SO2Ph), C(R = NO2), and D(R = C2(CN)3) were analysed using CAM-B3LYP, ωB97XD and LC-ωPBE hybrid DFT functionals in combination of the 6-311++G(d,p) standard basis set. The dipole moments, polarisabilities, HOMO-LUMO energy gaps, maximum absorption wavelengths and first hyperpolarisabilities were calculated in the gas phase and the obtained results are in good agreement with experimental NLO activity order A < B < C. Compared to synthesised dyes A-C, the designed dye D presents a longer maximum absorption wavelength and a lower HOMO-LUMO gap because of the appreciable stabilisation of its LUMO energy. These results were confirmed by the calculation of the total second-order stabilisation energy E(2) defined in the context of the NBO population analysis. Consequently, dye D is predicted to exhibit a higher first hyperpolarisability in comparison with dyes A-C. This result can be justified by the enhanced intramolecular charge transfer in dye D due to the stronger electron-withdrawing ability and the cumulative action of the long π-conjugation of the tricyanovinyl moiety. The very high total hyperpolarisability (27 times greater than that of para-nitroaniline) of the designed dye D suggests its promising use in organic NLO devices. [ABSTRACT FROM AUTHOR]

This study computes the potential energy curves of the X1Σ+, A1Π, B1Δ, C1Σ+, and D1Π states of AlO+ cation and the transition dipole moments between them. The orders of the rotationless radiative lifetimes are 10–100 μs for the A1Π state, 1–1000 ms for the B1Δ state, 10 ns for the first well and 100 ns for the second well of the C1Σ+ state, and 1 μs for the D1Π state. Emissions of the B1Δ–A1Π and D1Π–C1Σ+ systems are so weak that they are hardly measured via spectroscopy, the emissions of the C1Σ+–X1Σ+, C1Σ+–A1Π, and D1Π–X1Σ+ systems are so strong that they can be detected readily, and emissions of the A1Π–X1Σ+ and D1Π–A1Π systems can be observed through spectroscopy only by a significant effort. There is a strong great similarity between spontaneous emissions of the A1Π–X1Σ+ system of the AlO+ cation and the A2Π–X2Σ+ system of the AlO radical. The emissions of the A2Π–X2Σ+ system of the AlO radical have been measured in outer space Therefore, it is highly possible that the emissions of the A1Π–X1Σ+ system of the AlO+ cation can be detected in the astrophysical media. [ABSTRACT FROM AUTHOR]

The adiabatic potential energy curves for ground and many excited states of 1, 3Σ+, 1,3Π, 1,3Δ symmetries of the LiNa molecule have been performed. We have used an ab initio approach based on non-empirical pseudopotentials, parameterised l-dependent polarisation potentials and full configuration interaction calculations. In addition, the adiabatic potential energy curves determined in our previous work [Mabrouk and Berriche, J. Phys. B: At. Mol. Opt. Phys. 41, 155101 (2008).] are corrected by using a diabatisation procedure, based on the effective Hamiltonian theory and an effective metric. The diabatic permanent moments for first 10 1Σ+ electronic states show linear behaviours, especially at intermediate and large distance. The transition dipole moment between neighbour states has revealed many peaks located around the avoided crossing positions. The radial coupling between the adiabatic states was calculated using the Hellmann-Feynman formula and numerical differentiation of the rotation matrix. The first and the second derivatives revealed many peaks, associated to neutral-neutral and ionic-neutral crossings. Furthermore, the radial coupling is used to evaluate the adiabatic correction, which is found to be of an order of tens and hundreds of cm−1, especially of higher excited states. In addition, we have determined the vibrational level spacing for all studied states. [ABSTRACT FROM AUTHOR]

The first high-resolution infrared spectrum of CHD279Br has been investigated by Fourier transform spectroscopy in the range 940–1100 cm−1 at an unapodised resolution of 0.0025 cm−1. This spectral region is characterised by the v4 (1036.8389 cm−1) fundamental band, corresponding to the CD2 wagging mode. The rotational structure of the a- and c-type components of the hybrid band has been extensively assigned for transitions involving values of J and Ka up to 65 and 15, respectively. The ground state constants up to the quartic centrifugal distortion terms have been obtained for the first time by ground state combination differences from 5251 assigned transitions and subsequently employed for the evaluation of the band origin and the excited state parameters of v4. Watson's S-reduced Hamiltonian in the Ir representation has been used in the ro-vibrational analysis. The dipole moment ratio |Δμa/Δμc| of the band has been estimated to be 1.3 ± 0.1 from spectral simulations. [ABSTRACT FROM AUTHOR]

The first variational calculations of the rotational-vibrational levels of PF 3 are performed and intensities for dipole transitions between them computed. This is accomplished using new state of the art potential energy and dipole moment surfaces. This allows the infrared spectrum of PF 3 to be simulated, providing a complete overview of the ro-vibrational spectrum up to J=100 in the wavenumber range 0–3100 cm−1. The behaviour of PF 3 at high rotational excitations is also investigated. The formation of quasi-degenerate 6-fold rotational energy clusters at high rotational excitation are investigated up to J=270 and are found to occur around J=200. The clustering effect is analysed in terms of semi-classical rotational energy surfaces. [ABSTRACT FROM AUTHOR]

The liquid structure of the commonly used solvents dimethylformamide (DMF) and dimethylacetamide (DMA)were measured using state-of-the-art state neutron diffraction augmented with isotopic substitution (NDIS) and interpreted with empirical potential structure refinement (EPSR). Both solvents are found to develop rich local ordering with similar local packing densities, though with differences related to their three-dimensional molecular structure. While DMF's dipole preferentially orientates anti-parallel to maximise hydrogen bonding, DMA favours parallel arrangement maximising non-directional dispersive forces. The highly-developed local orientational structure found in these solvents rationalises their ability to solvate a range of charged and neutral nanomaterials and highlights that the understanding of nanomaterial dispersions is a multi-body problem in which the geometry of the molecule, as well its dipole moment, must be incorporated. [ABSTRACT FROM AUTHOR]

The neutron diffraction data of liquid bromoform (CHBr3) at 25°C was analysed using the Empirical Potential Structure Refinement technique in combination with H/D isotopic substitution. Compared to liquid chloroform (CHCl3), CHBr3 displays more spatially defined intermolecular contacts. A preference for polar stacking with collinear alignment of dipole moments is observed for the most closely approaching CHBr3 molecules, although to a lesser extent than in chloroform. Consistent with this, and in line with dielectric spectroscopy, the Kirkwood correlation factor from the structural model of CHBr3 is smaller than that of CHCl3. The net antiparallel alignment of dipole moments in CHBr3, as suggested by dielectric spectroscopy, must be due to weak but persistent long-range orientation correlations in CHBr3, which counteract the local polar stacking. [ABSTRACT FROM AUTHOR]

This work mainly investigates the transition dipole moments (TDMs) and radiative transition probabilities of dipole-allowed transitions between the , , , , , , , , and states of N2. Many of these transition properties are previously unknown. For completeness, another 14 electronic states that correlate to four lowest dissociation limits are also calculated. The potential energy curves (PECs) are calculated at the valence internally contracted multireference configuration-interaction (icMRCI) level of theory, along with the Davidson correction, the core-valence (CV) correction and the scalar relativistic correction, as well as the basis-set extrapolation. These corrections, especially the CV correction, greatly improve the accuracy of the PECs, as shown by the excellent agreement of the fitted spectroscopic parameters with the available experimental data. In order to verify the accuracy of transition properties, we calculate the Einstein coefficients of the extensively studied band transition systems and compute the radiative lifetimes of states, which are in good agreement with the experimental data. Similar accuracy can be assumed for the previously undetermined band transition systems. The large Einstein coefficients of these band systems can provide guidelines for observing such newly predicted band transitions in the appropriate spectroscopy experiments. [ABSTRACT FROM AUTHOR]

This work mainly investigates the transition dipole moments (TDMs) and radiative transition probabilities of dipole-allowed transitions between the , , , , , , , , and states of N2. Many of these transition properties are previously unknown. For completeness, another 14 electronic states that correlate to four lowest dissociation limits are also calculated. The potential energy curves (PECs) are calculated at the valence internally contracted multireference configuration-interaction (icMRCI) level of theory, along with the Davidson correction, the core-valence (CV) correction and the scalar relativistic correction, as well as the basis-set extrapolation. These corrections, especially the CV correction, greatly improve the accuracy of the PECs, as shown by the excellent agreement of the fitted spectroscopic parameters with the available experimental data. In order to verify the accuracy of transition properties, we calculate the Einstein coefficients of the extensively studied band transition systems and compute the radiative lifetimes of states, which are in good agreement with the experimental data. Similar accuracy can be assumed for the previously undetermined band transition systems. The large Einstein coefficients of these band systems can provide guidelines for observing such newly predicted band transitions in the appropriate spectroscopy experiments. [ABSTRACT FROM AUTHOR]

One-dimensional local mode XH-stretching (X = O, F and Cl) vibrational transition frequencies and intensities have been calculated for six small atmospheric relevant molecules. The calculations are done using Morse, Deng–Fan and numeric potentials at the CCSD(T)/aug-cc-pVTZ level of theory. Parameters of the Morse potential are found from the derivatives of the potential energy surface, with respect to the internal XH-stretching displacement coordinate, evaluated at the equilibrium geometry. Parameters of the Deng–Fan potential are obtained using the first two transition frequencies of the Morse potential. The dipole moment functions (DMFs) are represented by a sixth-order polynomial in the displacement coordinate fitted to dipole moment single points calculated with a finite field approach. Analytical matrix elements are derived and used to calculate oscillator strengths for the Morse and Deng–Fan potential. We compare calculated and experimentally determined oscillator strengths and transition frequencies, as well as displacement matrix elements of the different potentials. For the XH-stretching vibrations considered, the Deng–Fan potential predicts absorption intensities considerably better than the Morse potential. [ABSTRACT FROM AUTHOR]

Diffusion Monte Carlo (DMC) and Reptation Monte Carlo (RMC) methods, have been applied to study some properties of the NaK molecule. Hartree-Fock (HF), Density Functional (DFT) and single and double configuration interaction (SDCI) wavefunctions with a valence quadruple zeta atomic natural orbital (VQZ/ANO) basis set were used as trial wavefunctions. Values for the potential energy curve, dissociation energy and dipole moment were calculated for all methods and compared with experimental results and previous theoretical derivations. Quantum Monte Carlo (QMC) calculations were shown to be useful methods to recover correlation in NaK, essential to obtain a reasonable description of the molecule. The equilibrium distance yield a value close to the experimental one. The dissociation energy, however, is not so good, and the minimum error is about 4% of the experimental value, except when a coupled-clusters method is used. In this case, a conventional CCSD(T) calculation with an extended aug-pc-4 basis set gives a much better agreement to experiment. However, neither the CCSD(T) nor other MO and DFT methods are able to reproduce correctly the large dipole moment of this molecule. Even DMC methods with a simple HF trial wavefunction are able to give a better agreement to experiment, although they have a larger error bar. [ABSTRACT FROM AUTHOR]

The electronic ground states of MgLi and CaLi molecular ions are investigated for their spectroscopic constants and properties such as the dipole - and quadrupole moments, and static dipole polarisabilities. The quadrupole moments and the static dipole polarisabilities for these ions have been calculated and reported here, for the first time. The maximum possible error bars, arising due to the finite basis set and the exclusion of higher correlation effects beyond partial triples, are quoted for reliability. Further, the adiabatic effects such as diagonal Born-Oppenheimer corrections are also calculated for these molecules. The vibrational energies, the wavefunctions, and the relevant vibrational parameters are obtained by solving the vibrational Schrödinger equation using the potential energy curve and the permanent dipole moment curve of the molecular electronic ground state. Thereafter, spontaneous and black-body radiation induced transition rates are calculated to obtain the lifetimes of the vibrational states. The lifetime of rovibronic ground state for MgLi, at room temperature, is found to be and for CaLi it is . It has been observed that the lifetime of the highly excited vibrational state is several times larger than (comparable to) that of the vibrational ground state of MgLi (CaLi). In addition, a few low-lying electronic excited states of Σ and Π symmetries have been investigated for their electronic and vibrational properties, using EOM-CCSD method together with the QZ basis sets. [ABSTRACT FROM AUTHOR]

The electronic ground states of MgLi and CaLi molecular ions are investigated for their spectroscopic constants and properties such as the dipole - and quadrupole moments, and static dipole polarisabilities. The quadrupole moments and the static dipole polarisabilities for these ions have been calculated and reported here, for the first time. The maximum possible error bars, arising due to the finite basis set and the exclusion of higher correlation effects beyond partial triples, are quoted for reliability. Further, the adiabatic effects such as diagonal Born-Oppenheimer corrections are also calculated for these molecules. The vibrational energies, the wavefunctions, and the relevant vibrational parameters are obtained by solving the vibrational Schrödinger equation using the potential energy curve and the permanent dipole moment curve of the molecular electronic ground state. Thereafter, spontaneous and black-body radiation induced transition rates are calculated to obtain the lifetimes of the vibrational states. The lifetime of rovibronic ground state for MgLi, at room temperature, is found to be and for CaLi it is . It has been observed that the lifetime of the highly excited vibrational state is several times larger than (comparable to) that of the vibrational ground state of MgLi (CaLi). In addition, a few low-lying electronic excited states of Σ and Π symmetries have been investigated for their electronic and vibrational properties, using EOM-CCSD method together with the QZ basis sets. [ABSTRACT FROM AUTHOR]

We report experimental results on the broadening and shifting coefficients in a large interval of J quantum numbers in the fundamental and first overtone vibration-rotation bands of the HCl molecule in mixtures with helium. Many of the values, especially for the overtone transition, are novel. The uncertainties for the isotope-averaged broadening coefficients amount to 2% on average for the fundamental and 1.5% for the overtone bands. Shifts have a typical uncertainty of 3%. [ABSTRACT FROM AUTHOR]

Simulated external electric fields are applied to polarisable species containing either a monodisperse of bidisperse distribution of polarisabilities. The magnitude of the external field and the polarisabilities are systematically varied. The application of an external field (of sufficient magnitude) is found to induce chain formation (as expected). The monodisperse systems are found to ‘self-assemble’ with larger induced dipole moments effectively clustering in chains as a result of significant dipole-induced dipole effects. The distribution of the chain lengths is characterised as a function of the applied field and the atom polarisability. For the bidisperse systems, the external field induces chain formation and a partial segregation, in which the more polarisable species preferentially form chains. The chain lengths are again determined as a function of field strength and the atom polarisabilities. Scaling behaviour is analysed. [ABSTRACT FROM AUTHOR]

The physical interpretation of the limiting equivalent conductivity of binary electrolytes in solution, Λ0 (=Σi =+,- λ0 i), has been a challenge for almost a century. Here, as a follow-up on a preliminary communication [D. Fraenkel, Mol. Phys. 115, 2944 (2017)], a quantitative theoretical treatment is offered and fully developed for the limiting ionic equivalent conductivity, λ0 i, based on assuming that around any singled-out ion i in solution, there is an electrostatic atmosphere that includes oriented solvent dipoles and the counterion as 'charge density'. This leads to a simple mathematical expression for λ0 i as the result of the tandem operation of the dipole viscosity and dipole relaxation forces on the drifting ion. Contrary to literature teaching, λ0 i is found proportional to the effective ionic radius, ri. An 'electric ion-radius scale' derived from experimental λ0 i's for aqueous solutions, compares reasonably well with known ion-size scales. A newly defined solvent-specific dipole random-walk correction factor, ξ, is used for nonaqueous solvents as an adjustable parameter, to attain a parallel electric ion-size scale. The new theory provides overall a comprehensive view of the limiting ion mobility in solution, based on the ionic properties, solvent variables and universal constants. [ABSTRACT FROM AUTHOR]

The potential energy and spectroscopic constants of the ground and many excited states of the Be+He van der Waals system have been investigated using a one-electron pseudo-potential approach, which is used to replace the effect of the Be2+ core and the electron-He interactions by effective potentials. Furthermore, the core-core interactions are incorporated. This permits the reduction of the number of active electrons of the Be+He van der Waals system to only one electron. Therefore, the potential energy of the ground state as well as the excited states is performed at the SCF level and considering the spin-orbit interaction. The core-core interaction for Be2+He ground state is included using accurate CCSD (T) calculations. Then, the spectroscopic properties of the Be+He electronic states are extracted and compared with the previous theoretical and experimental studies. This comparison has shown a very good agreement for the ground and the first excited states. Moreover, the transition dipole moment has been determined for a large and dense grid of internuclear distances including the spin orbit effect. In addition, a vibrational spacing analysis for the Be2+He and Be+He ground states is performed to extract the He atomic polarisability. [ABSTRACT FROM AUTHOR]

The nanomaterials based on the In2O3molecule are widely used as catalysts and sensors among other applications. In the present study, we discuss the possibility of using nanoclusters of In2O3as molecular photomotors. A comparative analysis of the electronic structure of the In2O3molecule in the free state and in the crystal is performed. For the free In2O3molecule the geometry of its lowest structures, V-shape and linear, was optimised at the CCSD(T) level, which is the most precise computational method applied up to date to study In2O3. Using experimental crystallographic data, we determined the geometry of In2O3in the crystal. It has a zigzag, not symmetric structure and possesses a dipole moment with magnitude slightly smaller than that of the V-structure of the free molecule (the linear structure due to its symmetry has no dipole moment). According to the Natural Atomic population analysis, the chemical structure of the linear In2O3can be represented as O = In−O−In = O; the V-shaped molecule has the similar double- and single-bond structure. The construction of nanoclusters from ʻbricksʼ of In2O3with geometry extracted from crystal (or nanoclusters extracted directly from crystal) and their use as photo-driven molecular motors are discussed. [ABSTRACT FROM PUBLISHER]

A computational study of model complexes X3CH…YZ (X = B, F; YZ = BF, CO, N2) was undertaken to assess the effect of electron-donating and electron-withdrawing X atoms on the properties of the C–H…Y hydrogen bond. Sequential substitution of the B atoms in B3CH by F atoms to produce F3CH allowed for the elucidation of interesting trends in the corresponding hydrogen-bonded complexes. The dipole moments and the dipole moment derivative with respect to C–H bond displacement for the proton donors and the chemical hardness of the Y atom of the proton acceptor YZ were found to be useful parameters for understanding these trends. It was found that a positive dipole derivative favours red-shifted hydrogen bonds, whereas a negative dipole derivative favours blue-shifted hydrogen bonds. However, decreasing hardness of Y (which correlates with increasing intermolecular attraction) modifies the interaction such that either greater C–H bond extensions/red shifts or smaller C–H bond compressions/blue shifts are obtained. [ABSTRACT FROM PUBLISHER]

Highly correlated ab initio calculations were performed for accurate determination of γ (A² Σ+-X² П) and β (B2 П-X² П) band systems of NO molecule. Highly accurate multi-reference configuration inter-action approach was used to investigate the potential energy curves (PECs) and transition dipole moment curves. We correctly and fully described their diffuse wave functions by the obvious balance between the valence and Rydberg character of the X² П,A² Σ+, B2 П, C² П and D² Σ+ states. The PECs of the three states (X²П, A² Σ+ and B² П) by using the aug-cc-pV5Z (aV5Z) basis set for N and O atoms agreed well with the Rydberg--Klein--Rees potential. Moreover, the Einstein A coefficients were calculated to predict the lifetimes, where the vibrational bands included v' = 0-8, v" = 0-29 for γ system and v' = 0-11, v" = 0-31 for β system. The spectral line intensities of the γ and β systems for atmosphere and high temperature were provided. [ABSTRACT FROM AUTHOR]

The influence of ring puckering angle on the multipole moments of sixteen four-membered heterocycles (1-16) was theoretically estimated using MP2 and different DFTs in combination with the 6-31+G(d,p) basis set. To obtain an accurate evaluation, CCSD/cc-pVDZ level and, the MP2 and PBE1PBE methods in combination with the aug-cc-pVDZ and aug-cc-pVTZ basis sets were performed on the planar geometries of 1-16. In general, the DFT and MP2 approaches provided an identical dependence of the electrical properties with the puckering angle for 1-16. Quantitatively, the quality of the level of theory and basis sets affects significant the predictions of the multipole moments, in particular for the heterocycles containing C=O and C=S bonds. Convergence basis sets within the MP2 and PBE1PBE approximations are reached in the dipole moment calculations when the aug-cc-pVTZ basis set is used, while the quadrupole and octupole moment computations require a larger basis set than aug-cc-pVTZ. On the other hand, the multipole moments showed a strong dependence with the molecular geometry and the nature of the carbon-heteroatombonds. Specifically, the C-X bond determines the behavior of the μ(φ), θ(φ) and 'Ω(φ) functions, while the C=Y bond plays an important role in the magnitude of the studied properties. [ABSTRACT FROM AUTHOR]

The properties of carbon monoxide in its ground and two lowest lying excited states are investigated by conventional and time-dependent (TD) density functional theory (DFT). The dipole moment is decomposed into atomic polarisation (AP) and inter-atomic charge transfer (CT) contributions according to the quantum theory of atoms in molecules (QTAIM). Considerable AP and CT contributions cancel in the ground state (S0) resulting in its known negligible dipole moment. This balance is disturbed in the lowest triplet (T1) and singlet (S1) excited states, resulting in dipole moments of 1.57 D forT1and 0.49 D forS1. The AP decreases by 2.5 D on excitation to either state but the opposing CT is reduced by 0.8 D forT1and by 1.8 D forS1, insufficient for cancellation. These excitations induce charge transfer from O to C which drives dipole changes accompanied by a weakening of the C–O bond, more pronounced in theS1state, as trends in bond lengths, vibrational frequencies, and QTAIM properties suggest. The charge–charge flux–dipole flux (CCFDF) model in terms of QTAIM parameters reveals that the vibrational stretching band weakening on excitation is predominantly due to changes in atomic charges. [ABSTRACT FROM AUTHOR]