Vibrational Polarizabilities Research Articles

Synthesis, crystal structure, spectroscopic, electronic and vibrational properties of N′-[(E)-3-pyridinylmethylene]nicotinohydrazide trihydrate: Experimental and computational study

N′-[(E)-3-pyridinylmethylene]nicotinohydrazide trihydrate (C12H10N4O·3(H2O)) was synthesized and its structure was determined by single crystal X-ray diffraction method. X-ray analysis showed that the compound crystalized in the triclinic system P-1 with a = 7.1134 (3) Å, b = 10.0208 (4) Å, c = 10.3601 (4) Å, α = 96.386 (3)°, β = 96.995 (3)°, γ = 101.219 (4)°, V = 712.05 (5) Å3 and Z = 2 and exhibits that the title compound (I) consists of N′-[(E)-3-pyridinylmethylene]nicotinohydrazide (II) (C12H10N4O), and three water molecules of crystallization. The two water molecules are attached to the third water molecule through intermolecular two OH…O hydrogen bonds. At the same time, this water molecule is linked to the NH amide group of the hydrazone by an intermolecular NH…O hydrogen bond. Hirshfeld surface (HS) analyses were carried out are to visualise the intermolecular interactions in the crystals of Compound I. The geometric optimization of the titled compound has been carried out by different computational methods such as by Hatree Fock (HF) and Density Functional Theory (DFT) methods with the 6–311++G (d,p) basis set. The vibrational frequency, dipole moment (μ), polarizability (α), hyperpolarizability (β), and electronic properties including the highest occupied molecular orbital-lowest unoccupied molecular orbital (HOMO–LUMO) of the compound have been calculated at the level of both theories. In the results of crystal analysis and geometry calculations of the compound I, it was observed that intermolecular hydrogen bonds, N2H2A…O3, O3H31…O2 and O3H32…O4, were formed. The energy band gap (Eg = ELUMO-EHOMO) values were also obtained by using ELUMO and EHOMO at the level of both theories. The value of equilibrium (ground state) dipole moment of the studied molecule was calculated to be 8.31 Debye in B3LYP and 7.55 Debye in HF. The calculated hyperpolarizability values at the B3LYP/6–311++G(d,p) of the compound are 2.53 × 10−30 esu and this value corresponds to 6.79 times the hyperpolarizability value of urea.

Temperature-dependent index of refraction Sellmeier model for crystalline and polycrystalline materials.

The temperature dependence of optical window materials remains an important issue for a variety of applications from spacecraft, laser components, to high-speed aircraft. Concerning the refractive index in regions of transparency, current models are empirically based polynomial fits for the Sellmeier model strength and mode location parameters. These polynomial fit functions limit the ability to accurately extrapolate beyond the experimental range used to develop the fit functions. Thus, the development of a physics-based model as a function of temperature is an important goal for these critical materials. Such a model will allow extrapolation to higher and lower temperatures as long as the physical mechanisms do not change. For vibrational modes, a thermal average of the anharmonically shifted energy levels is investigated and compared to experimental data. The first anharmonic term can be estimated using the Morse potential based on a multiphonon absorption model. Experimentally, these modes redshift, and this is consistent with the developed temperature-dependent index of refraction Sellmeier model. This redshifting phenomena can also be applied to electronic transition shifts. In addition, the temperature-dependent oscillator number density can be obtained from known expansion coefficient models and experimental data. Other model parameters, in particular the electronic and vibrational mode polarizability, still need experimental grounding for a given material. The method is incorporated into a modified Sellmeier model format.

Effect of vibrational resonances and dynamic polarizability on the Raman spectrum of furfural: A vibrational coupled cluster study

The Raman spectrum of furfural is computed and analyzed using the Vibrational Coupled Cluster Method (VCCM). Furfural has immense applications in organic synthesis, electrocatalysis and energy conversion process. The experimental Raman spectrum of furfural is congested and broad, even in the medium energy regions like C-C stretching and CO stretching regions. We extensively analyze the Fermi and higher quanta resonance effects on the Raman spectrum by examining the VCCM wavefunctions. In addition, a systematic study on the effect of incident frequency on the anharmonic Raman activity is carried out by comparing the results with incident wavelengths 325.0 nm and 632.8 nm against static polarizability.

Temperature Dependence of Non-Condon Effects in Two-Dimensional Vibrational Spectroscopy of Water.

Non-Condon effects in vibrational spectroscopy refers to the dependence of a molecule's vibrational transition dipole and polarizability on the coordinates of the surrounding environment. Earlier studies have shown that such effects can be pronounced for hydrogen-bonded systems like liquid water. Here, we present a theoretical study of two-dimensional vibrational spectroscopy under the non-Condon and Condon approximations at varying temperatures. We have performed calculations of both two-dimensional infrared and two-dimensional vibrational Raman spectra to gain insights into the temperature dependence of non-Condon effects in nonlinear vibrational spectroscopy. The two-dimensional spectra are calculated for the OH vibration of interest in the isotopic dilution limit where the coupling between the oscillators is ignored. Generally, both the infrared and Raman line shapes undergo red shifts with decrease in temperature due to strengthening of hydrogen bonds and decrease in the fraction of OH modes with weaker or no hydrogen bonds. The infrared line shape is further red-shifted under the non-Condon effects at a given temperature, while the Raman line shape does not show any such red shift due to non-Condon effects. The spectral dynamics becomes slower on decrease of temperature due to slower hydrogen bond relaxation and, for a given temperature, the spectral diffusion occurs at a faster rate upon inclusion of non-Condon effects. The time scales of spectral diffusion extracted from different metrics agree well with each other and also with experiments. The changes in the spectrum due to non-Condon effects are found to be more significant at lower temperatures.

Optical Effect Modulation in Polarized Raman Spectroscopy of Transparent Layered α-MoO3.

Optical anisotropy, which is quantified by birefringence (Δn) and linear dichroism (Δk), can significantly modulate the angle-resolved polarized Raman spectroscopy (ARPRS) response of anisotropic layered materials (ALMs) by external interference. This work studies the separate modulation of birefringence on the ARPRS response and the intrinsic response by selecting transparent birefringent crystal α-MoO3 as an excellent platform. It is found that there are several anomalous ARPRS responses in α-MoO3 that cannot be reproduced by the real Raman tensor widely used in non-absorbing materials; however, they can be well explained by considering the birefringence-induced Raman selection rules. Moreover, the systematic thickness-dependent study indicates that birefringence modulates the ARPRS response to render an interference pattern; however, the amplitude of modulation is considerably lower than that by linear dichroism as occurred in black phosphorous. This weak modulation brings convenience to the crystal orientation determination of transparent ALMs. Combining the atomic vibrational pattern and bond polarizability model, the intrinsic ARPRS response of α-MoO3 is analyzed, giving the physical origins of the Raman anisotropy. This study employs α-MoO3 as an example, although it is generally applicable to all transparent birefringent ALMs.

Raman and UVN+LWIR LIBS detection system for in-situ surface chemical identification

Laser Induced Breakdown Spectroscopy (LIBS) in the Ultra Violet/Visible/Near-IR (UVN) spectral range is a powerful analytical tool that facilitates the interpretation of Raman spectroscopic data by providing additional details in elemental chemistry. To acquire the complete information of molecular vibrations for more accurate and precise chemical bonding and structural analysis, an ideal in situ optical sensing facility should be able to rapidly probe the broad vibrational dipole and polarizability responses of molecules by acquiring both Raman scattering and mid-IR emission spectroscopic signatures. Recently, the research team at Brimrose has developed a novel optical technology, Long-Wave IR (LWIR) LIBS. Critical experimental approaches were made to capture the infrared molecular emission signatures from vibrationally excited intact samples excited by laser-induced plasma in a LIBS event. LWIR LIBS is the only fieldable mid-IR emission spectroscopic technique to-date that that offers the same instrumental and analytical advantages of both UVN LIBS and Raman spectroscopy in in-situ stand-off field applications and can perform rapid and comprehensive molecular structure analysis without any sample-preparation.•A single excitation laser pulse is used to trigger both UVN and LWIR spectrometers simultaneously.•Time-resolved UVN-LWIR LIBS measurements showed the evolution of both atomic and molecular signature emissions of target compounds in the laser-induced plasma.•The technique was applied to the characterization of mineral and organic compounds in planetary analog samples.

Impact of molecular chain length on polarizabilities of model acenes and oligomers

Abstract A systematic quantum chemical study of model linear oligomers and their ring-fused (condensed) analogues based on six-membered and five-membered aromatic units is presented. Static electric polarizabilities were calculated for optimal geometries. The dependence of electronic and vibrational polarizability contributions on the molecular size was discussed and polymer limits were estimated. The presence of a diradical electronic structure in fused six-membered compounds significantly increases the polarizability values.

The coverage dependence of the infrared absorption of CO adsorbed to NaCl(100).

CO adsorbed to NaCl(100) exhibits perhaps the weakest possible coupling between the adsorbate and solid. It is, therefore, an ideal system to observe the influence of adsorbate-adsorbate interactions on infrared absorption. In this work, we report polarized FTIR absorption spectra of CO/NaCl(100) as a function of coverage (0.02 ≤ θ ≤ 1 ML), where the coverage has been quantitatively determined by temperature-programmed desorption and molecular beam dosing. We extend a previous semi-empirical model designed to describe the screening of the local electric field due to dipole-dipole interactions in a CO monolayer. The extended model applies to sub-monolayer coverages and describes properly the electric field of the absorbed radiation at the vacuum-substrate interface. Fitting this model to coverage-dependent IR absorption data allows us to derive the vibrational and electronic polarizabilities [χv = 0.0435(14) Å3, χe = 3.30(36) Å3] and the integrated absorption cross section of 2.51(8) × 10-17 cm/molecule for an isolated CO molecule adsorbed at the NaCl (100) surface. The determined integrated absorption cross section is substantially smaller than that of gas phase CO.

Can Density Functional Theory Be Trusted for High-Order Electric Properties? The Case of Hydrogen-Bonded Complexes.

This work reports on an extensive assessment of the performance of a wide palette of density functional approximations in predicting the (high-order) electric properties of hydrogen-bonded complexes. To this end, we compute the electronic and vibrational contributions to the electric polarizability and the first and second hyperpolarizabilities, using the CCSD(T)/aug-cc-pVTZ level of theory as reference. For all the studied properties, the average absolute errors below 20% can only be obtained using the CAM-B3LYP functional, while LC-BLYP and MN15 are shown to be only slightly less accurate (average absolute errors not exceeding 30%). Among Minnesota density functionals, i.e., M06, M06-2X, and MN15, we only recommend the latter one, which quite accurately predicts the electronic and vibrational (hyper)polarizabilities. We also analyze the optimal tuning of the range-separation parameter μ for the LC-BLYP functional, finding that this approach does not bring any systematic improvement in the predictions of electronic and vibrational (hyper)polarizabilities and the accuracy of computed properties is largely system-dependent. Finally, we report huge errors in predicting the vibrational second hyperpolarizability by ωB97X, M06, and M06-2X functionals. Based on the explicit evaluation of anharmonic terms contributing to the second hyperpolarizability, this failure is traced down to a poor determination of third- and fourth-order energy derivatives with respect to normal modes. These results reveal serious flaws of some density functional approximations and suggest caution in selecting the appropriate functional to calculate not only electronic and vibrational (hyper)polarizabilities but also other molecular properties that contain vibrational anharmonic contributions.

Molecular Docking and Comparative Vibrational Spectroscopic Analysis, HOMO-LUMO, Polarizabilities, and Hyperpolarizabilities of N-(4-Bromophenyl)-4-Nitrobenzamide by Different DFT (B3LYP, B3PW91, and MPW1PW91) Methods

We have recorded and analyzed FTIR and FT-Raman spectra of N-(4-Bromophenyl)-4-nitrobenzamide. Here, we have presented a comparative study between different method combinations. Firstly, we have done its geometry optimization. After this, we have calculated fundamental vibrational frequencies with intensity using different methods like B3PW91, MPW1PW91, and B3LYP/6-311G (d, p). The complete vibrational assignments of wavenumbers are made on the basis of potential energy distribution (PED). The result from the calculated spectra of the title compound shows excellent agreement with experimental spectra. We have also computed HOMO-LUMO gap and plotted frontier orbital HOMO-LUMO surfaces, Molecular electrostatic potential surfaces to explain the reactive nature of N-(4-bromophenyl)-4-nitrobenzamide. The values of hyper polarizability show a probable use of these compounds in electro-optical applications. From the result of docking picture, we can say that this compound effectively act as an antibacterial drug.

Close Relationships between NMR J-Coupling Alternation (JCA) and Molecular Properties of Carbon Chains.

We propose a J-coupling alternation (JCA) value that is demonstrated to be a suitable parameter to evaluate the nuclear magnetic resonance (NMR) indirect spin-spin coupling constants (SSCCs) as a function of molecular properties of chains by increasing their length. As an application, we report a theoretical study of the SSCCs for the interactions between neighbor nuclei in increasingly patterned carbon chains within density functional theory. First, we examine the J-coupling constants between 1H and 13C nuclei ( n JHC) considering the separation distance, as well as between two adjacent 13C nuclei (1 JCC) considering their relative positions in polyynes and cumulenes. Further, we define and determine JCA in terms of the differences of 1 JCC, which is investigated as a function of several molecular properties, e.g., cohesive energy, characteristic vibrational frequency, average polarizability, and energy gap of the systems. We also determine JCA for other types of carbon chains, such as diphenyl-capped polyynes, polyacetylene and polythiophene. The behavior of JCA as a function of the energy gap may be related to highly π-conjugated low-band-gap carbon chains. Overall, JCA correlates very well with the electronic properties of these chains, especially with their energy gap, exhibiting positive values for pristine polyyne and polythiophene and negative values for pristine cumulene and plyacetylene. These findings indicate an alternative way to establish an appropriate SSCC descriptor that characterizes the electronic nature of the system, such as the proposed JCA value averaging the whole system, instead of using only the individual J-coupling values to give insights into the properties of large and extended systems.

Molecular structure, vibrational, optical and second order polarizabilities of (E)-1-(2′,4′-Dihydroxy-phenyl)-3-(2,3-dimethoxyphenyl)-propenone chalcone derivative: a quantum computational approach

In this report, geometrical optimization, spectroscopic analysis, photophysical and nonlinear optical studies of (E)-1-(2′,4′-Dihydroxy-phenyl)-3-(2,3-dimethoxyphenyl)-propenone (2,3,4 DHMP) were investigated by utilizing DFT/B3LYP, DFT/CAM-B3LYP, DFT/LC-BLYP, DFT/PBE1PBE, DFT/WB97XD, DFT/TPSS and DFT/M06-2X at 6-31++G** basis set and obtained outcomes are compared. The geometrical parameters are in close covenant with experimental (An excellent concurrence between geometrical parameters and the experimental results was observed). The detailed FT-IR and FT-Raman spectroscopic analyses is carried out. TD-DFT is used to analyze UV–visible spectrum at dissimilar methods and the value of λabs is observed at ~ 400 nm. Molecular orbitals and electrostatic potential were calculated and discussed. Second-order polarizability was computed which is ~ 21 times larger compared to urea. High value of polarizability makes current compound as a good applicant for NLO applications.

Partitioning of interaction-induced nonlinear optical properties of molecular complexes. I. Hydrogen-bonded systems.

Understanding the effects of different fundamental intermolecular interactions on nonlinear optical properties is crucial for proposing efficient strategies to obtain new materials with tailored properties. In this study, we computed the electronic and vibrational (hyper)polarizabilities of ten hydrogen-bonded molecular complexes employing the MP2, CCSD and CCSD(T) methods combined with the aug-cc-pVTZ basis set. The vibrational contributions to hyperpolarizabilities included nuclear-relaxation anharmonic corrections. The effect of intermolecular interactions was analyzed in terms of excess properties, which are defined as the difference between a property of the complex and the net properties of the noninteracting subsystems. Considering systems covering a wide range of hydrogen bond strengths, the electronic and vibrational excess (hyper)polarizabilities were decomposed into different interaction energy contributions (electrostatic, exchange, induction and dispersion). This systematic study, the very first of this kind, revealed that the physical origins of the electronic and vibrational excess properties are completely different. In the case of vibrational contributions, the decomposition pattern is very similar for the polarizability and first and second hyperpolarizabilities. The exchange contributions to excess vibrational properties are the largest and they have an opposite sign to the electrostatic, induction and dispersion terms. On the other hand, no general patterns can be established for the electronic excess properties.

Spectroscopic and non-linear optical studies of two novel optical limiters from dichloroaniline family crystals: 3,4-Dichloroaniline and 3,5-dichloroaniline

Two organic crystals of the isomeric forms of dichloroanilines such as 3, 4-dichloroaniline (3,4-DCA) and 3, 5-dichloroaniline (3,5-DCA) were grown by slow evaporation method and characterized by various analytical techniques. The vibrational normal modes of the samples were theoretically predicted using the scaled quantum mechanical force field procedures with the DFT level calculation and the potential energy distributions of the individual modes were estimated using the normal coordinate analysis. Fermi doublets and Evans holes were identified in the vibrational spectra of samples. The nuclear relaxation contribution to the vibrational polarizabilities and hyperpolarizabilities for the normal modes of the molecules were quantitatively estimated using the DFT method. The results of the calculated NLO responses showed that the vibrational mean contributions to the static polarizabilities and hyperpolarizabilities were smaller than the corresponding electronic contributions for the molecules. The Kurtz and Perry powder SHG efficiencies were measured and both samples have generated the second-harmonics of the fundamentals. The open-aperture Z-scan study results proposed the superior optical limiting property of 3,5-DCA with respect to 3,4-DCA.

Molecular structure, vibrational, factor group, optical and second order polarizability analysis of the l-prolinium trichloroacetate: A computational approach

For the first time the molecular structure, vibrational, optical and nonlinear optical properties of the l-prolinium trichloroacetate (LPTCA) have been determined by B3LYP/6-31++G** level of theory and the obtained properties are well correlated with the experimental report. The factor group investigation was also made and discussed. In the continuation of theoretical studies the TD-DFT approach is applied to study the various key properties. The calculated absorption wavelength value is found at λexc=174nm (7eV). The dipole moment and first order hyperpolarizability were also calculated and found to be comparable with urea. Further, global chemical reactivity descriptors (GCRD), frontier molecular orbitals and molecular electrostatic potential (MEP) are discussed. All the properties suggest that the present material may be a good contender for optoelectronic devices.

Communication: Understanding molecular representations in machine learning: The role of uniqueness and target similarity.

The predictive accuracy of Machine Learning (ML) models of molecular properties depends on the choice of the molecular representation. Inspired by the postulates of quantum mechanics, we introduce a hierarchy of representations which meet uniqueness and target similarity criteria. To systematically control target similarity, we simply rely on interatomic many body expansions, as implemented in universal force-fields, including Bonding, Angular (BA), and higher order terms. Addition of higher order contributions systematically increases similarity to the true potential energy and predictive accuracy of the resulting ML models. We report numerical evidence for the performance of BAML models trained on molecular properties pre-calculated at electron-correlated and density functional theory level of theory for thousands of small organic molecules. Properties studied include enthalpies and free energies of atomization, heat capacity, zero-point vibrational energies, dipole-moment, polarizability, HOMO/LUMO energies and gap, ionization potential, electron affinity, and electronic excitations. After training, BAML predicts energies or electronic properties of out-of-sample molecules with unprecedented accuracy and speed.

Simulations of the infrared, Raman, and 2D-IR photon echo spectra of water in nanoscale silica pores

Vibrational spectroscopy is frequently used to characterize nanoconfined liquids and probe the effect of the confining framework on the liquid structure and dynamics relative to the corresponding bulk fluid. However, it is still unclear what molecular-level information can be obtained from such measurements. In this paper, we address this question by using molecular dynamics (MD) simulations to reproduce the linear infrared (IR), Raman, and two-dimensional IR (2D-IR) photon echo spectra for water confined within hydrophilic (hydroxyl-terminated) silica mesopores. To simplify the spectra the OH stretching region of isotopically dilute HOD in D2O is considered. An empirical mapping approach is used to obtain the OH vibrational frequencies, transition dipoles, and transition polarizabilities from the MD simulations. The simulated linear IR and Raman spectra are in good general agreement with measured spectra of water in mesoporous silica reported in the literature. The key effect of confinement on the water spectrum is a vibrational blueshift for OH groups that are closest to the pore interface. The blueshift can be attributed to the weaker hydrogen bonds (H-bonds) formed between the OH groups and silica oxygen acceptors. Non-Condon effects greatly diminish the contribution of these OH moieties to the linear IR spectrum, but these weaker H-bonds are readily apparent in the Raman spectrum. The 2D-IR spectra have not yet been measured and thus the present results represent a prediction. The simulated spectra indicates that it should be possible to probe the slower spectral diffusion of confined water compared to the bulk liquid by analysis of the 2D-IR spectra.

On the physical origins of interaction-induced vibrational (hyper)polarizabilities.

This paper presents the results of a pioneering exploration of the physical origins of vibrational contributions to the interaction-induced electric properties of molecular complexes. In order to analyze the excess nuclear relaxation (hyper)polarizabilities, a new scheme was proposed which relies on the computationally efficient Bishop-Hasan-Kirtman method for determining the nuclear relaxation contributions to electric properties. The extension presented herein is general and can be used with any interaction-energy partitioning method. As an example, in this study we employed the variational-perturbational interaction-energy decomposition scheme (at the MP2/aug-cc-pVQZ level) and the extended transition state method by employing three exchange-correlation functionals (BLYP, LC-BLYP, and LC-BLYP-dDsC) to study the excess properties of the HCN dimer. It was observed that the first-order electrostatic contribution to the excess nuclear relaxation polarizability cancels with the negative exchange repulsion term out to a large extent, resulting in a positive value of Δα(nr) due to the contributions from the delocalization and the dispersion terms. In the case of the excess nuclear relaxation first hyperpolarizability, the pattern of interaction contributions is very similar to that for Δα(nr), both in terms of their sign as well as relative magnitude. Finally, our results show that the LC-BLYP and LC-BLYP-dDsC functionals, which yield smaller values of the orbital relaxation term than BLYP, are more successful in predicting excess properties.

Ab initio investigation of electronic and vibrational contributions to linear and nonlinear dielectric properties of ice.

Electronic and vibrational contributions to the static and dynamic (hyper)polarizability tensors of ice XI and model structures of ordinary hexagonal ice have been theoretically investigated. Calculations were carried out by the finite field nuclear relaxation method for periodic systems (FF-NR) recently implemented in the CRYSTAL code, using the coupled-perturbed Kohn-Sham approach (CPKS) for evaluating the required electronic properties. The effect of structure on the static electronic polarizabilities (dielectric constants) and second-hyperpolarizabilities is minimal. On the other hand, the vibrational contributions to the polarizabilities were found to be significant. A reliable evaluation of these (ionic) contributions allows one to discriminate amongst ice phases characterized by different degrees of proton-order, primarily through differences caused by librational motions. Transverse static and dynamic vibrational (hyper)polarizabilities were found by extrapolating calculations for slabs of increasing size, in order to eliminate substantial surface contributions.

Stereo-electronic, vibrational, and environmental contributions to polarizabilities of large molecular systems: a feasible anharmonic protocol.

Reliable computations of linear and non-linear optical properties of molecular systems in condensed phases require a proper account of stereo-electronic, vibrational, and environmental effects. In the framework of density functional theory, these effects can be accurately introduced using second-order vibrational perturbation theory in conjunction with polarizable continuum models. We illustrate the combination of an anharmonic description of the ground-state potential energy surface with solvation effects treated with the polarizable continuum model (PCM) in the calculation of the electronic, zero-point, and pure vibrational polarizabilities of selected systems. The description of the solvation environment is enriched by taking into account the dynamical aspects of the solute-solvent interactions through the inclusion of both electronic and vibrational non-equilbrium effects, as well as the direct effect of the solvent on the electric field that generates the molecular response (local field effect). This treatment yields accurate results which can be directly compared with experimental findings without the need of empirical corrections.