Determination Of Dipole Moments Research Articles

Accurate determination of 6,7Li nuclear magnetic moments

We report an accurate determination of the nuclear magnetic dipole moments of 6,7Li from the measured ratio of the nuclear and the electron g-factors in atomic Li. The obtained results significantly improve upon the literature values and stress the importance of reliable theoretical calculations of the nuclear shielding corrections.

Electric Dipole Moments from Stark Effect in Supersonic Expansion: n-Propanol, n-Butanol, and n-Butyl Cyanide.

The orientation and magnitude of the molecular electric dipole moment are key properties relevant to topics ranging from the nature of intermolecular interactions to the quantitative analysis of complex gas-phase mixtures, such as chemistry in astrophysical environments. Stark effect measurements on rotational spectra have been the method of choice for isolated molecules but have become less common with the practical disappearance of Stark modulation spectrometers. Their role has been taken over by supersonic expansion measurements within a Fabry-Perot resonator cavity, which introduces specific technical problems that need to be overcome. Several of the adopted solutions are described and compared. Presently, we report precise electric dipole moment determinations for the two most stable conformers of the selected molecules of confirmed or potential astrophysical relevance: n-propanol, n-butanol, and n-butyl cyanide. All dipole moment components have been precisely determined at supersonic expansion conditions by employing specially designed Stark electrodes and a computer program for fitting the measured Stark shifts, inclusive of cases with resolved nuclear quadrupole hyperfine structure. The experimental values are compared with suitable quantum chemistry computations. It is found that, among the tested levels of computation, vibrationally averaged dipole moments are the closest to the observation and the molecular values are, as in the lighter molecules in the series, largely determined by the hydroxyl or nitrile groups.

Determination of transition dipole moments of solids with high-order harmonics driven by multicycle ultrashort pulses

We propose an all-optical method to reconstruct the transition dipole moment of solid materials. Our method is realized by high-order harmonic generation driving by a multicycle laser pulse. The relations between the transition dipole moment and the harmonic yield are established. It is found that the transition dipole phase is related to the intensity ratio of the neighboring odd and even harmonics, and the modulus of the transition dipole moment is related to the odd harmonics. We investigate the high-order harmonic generation in symmetric crystals and asymmetric crystals by solving the semiconductor Bloch equations and use these relations to successfully reconstruct their relative transition dipole moments.

Solvation and Solvatochromism: An Overview#

Different examples of solvatochromic shifts are shown and the theory that explain the non-specific general solvent effects are discussed here. The use of solvatochromic shifts for the determination of excited state dipole moment has been presented in detail in connection with a brief overview of different solvent polarity functions. The lack of proper theoretical expressions to explain the specific solvent effect stimulates to introduce the concept of “empirical measures of solvent polarity”, based on well known, convenient, solvent sensitive model processes. Various solvent sensitive polarity probes are discussed in this context. So far as quantitative estimation of various parameters responsible for the observed solvatochromic shifts are concerned, introduction of multiparameter approaches, its application in recent years has been carefully analyzed. The review also focuses some of the recent developments on the theoretical calculations of various solute-solvent interaction parameters based on quantum mechanical approaches. This issue solvation interaction by the use of mixed solvents has been discussed in detail, starting from the early development of the theories related to preferential solvation to the recent scenario, with a critical survey on the application of the concept of preferential solvation in the solubilization of drugs, polymers considering the emerging ‘green approach’ in recent years.

The Role of Hydrogen Bonding in Paracetamol-Solvent and Paracetamol-Hydrogel Matrix Interactions.

The photophysical and photochemical properties of antipyretic drug – paracetamol (PAR) and its two analogs with different substituents (acetanilide (ACT) and N-ethylaniline (NEA)) in 14 solvents of different polarity were investigated by the use of steady–state spectroscopic technique and quantum–chemical calculations. As expected, the results show that the spectroscopic behavior of PAR, ACT, and NEA is highly dependent on the nature of the solute–solvent interactions (non-specific (dipole-dipole) and specific (hydrogen bonding)). To characterize these interactions, the multiparameter regression analysis proposed by Catalán was used. In order to obtain a deeper insight into the electronic and optical properties of the studied molecules, the difference of the dipole moments of a molecule in the ground and excited state were determined using the theory proposed by Lippert, Mataga, McRae, Bakhshiev, Bilot, and Kawski. Additionally, the influence of the solute polarizability on the determined dipole moments was discussed. The results of the solvatochromic studies were related to the observations of the release kinetics of PAR, ACT, and NEA from polyurethane hydrogels. The release kinetics was analyzed using the Korsmayer-Peppas and Hopfenberg models. Finally, the influence of the functional groups of the investigated compounds on the release time from the hydrogel matrix was analyzed.

Multi-property evaluation for a gas sample based on the acoustic and electromagnetic resonances measurement in a cylindrical cavity

This study proposes a multi-property evaluation method for a gas sample on the basis of sound speed and relative permittivity measurements by using a cylindrical acoustic-electromagnetic resonator. Validity and reliability of the present apparatus were confirmed from the measurement result for Ar with the relative standard uncertainties of 2 × 10−4 for the sound speed and 4 × 10−6 for the relative permittivity. The sound speed and the relative permittivity measurements for trans-1-chloro-3,3,3-trifluoropropene, which is known as R1233zd(E), were carried out in the wide temperature and pressure ranges to demonstrate the multi-property evaluation for a polar molecular sample. Firstly, specific heat capacity and molar polarization in the ideal-gas state were derived from the sound speed and the relative permittivity data, respectively, based on the acoustic- and the dielectric-virial equations. Secondly, linear regression of the ideal-gas molar polarization and temperature data leaded information of dipole moment and molecular polarizability in accordance with Debye equation. The density-virial coefficients were deduced by use of an empirical correlation with the determined dipole moment on the basis of the corresponding states principle so that the acoustic- and the dielectric-virial coefficients were separately determined from polynomial regression analysis of the sound speed and the relative permittivity data, respectively. Finally, the relative permittivity data in combination with the determined dielectric-virial coefficients yield the value of density. The acquired multi-property data for R1233zd(E) were compared with the existing equation of state or reference model.

The Origin of the Chiral gauche-Conformation Preferences in Halomethyl Methyl Ethers. A Hybrid-Density Functional Study and Natural Bond Orbital Interpretation

The effects of the stereoelectronic interaction on the structural and conformational properties of fluoromethyl methyl ether (1) and its analogues containing Cl (2), Br (3), and I (4) atoms were investigated by means of hybrid-density functional based method (B3LYP/Def2-TZVPP) and natural bond orbital (NBO) interpretation. Consistent with the reported experimental data, the chiral gauche conformations of compounds 1–4 are more stable than their corresponding anti conformations. The results showed that the energy barriers of the racemization processes of the chiral gauche-conformations of compounds 1–4 via the plane symmetrical anti conformations are smaller than the plane symmetrical eclipsed transition structures. According to the NBO analysis, the hyperconjugative generalized anomeric effect (HCGAE) increased from compound 1 to compound 4, which explains the increase of the energy discrepancy between their corresponding chiral gauche- and plane symmetrical anti-conformations. In contrast to the trend for the HCGAE, the determined dipole moment discrepancy between the chiral gauche- and plane symmetrical anti-conformations (µanti–µgauche) reduced from compound 1 to compound 4. This fact reveals that there is no correlation between the variations of the conformational preferences in compounds 1–4 and the electrostatic effects associated with the dipole–dipole interactions. There is an excellent agreement between the racemization energy barriers and the proportion between the GAE for compounds 2–4 and compound 1 (i.e., GAEx/GAE1) as well as the difference between the Wiberg Bond Indexes of C1–O2 bonds (Δ[WBIanti-gauche(C1–O2)]). The associations between the HCGAE, pairwise steric exchange energies (PSEE), WBI, dipole moments, orbital integrals, structural parameters, and conformational behaviors of compounds 1–4 have been studied.

Ortorombik metaborik asit molekülünün moleküler yapısı ve elektronik özellikleri üzerindeki konformasyonel etkinin teorik olarak incelenmesi

In the present study, conformational analysis, Nonlinear Optical (NLO) behavior, vibrational spectra, electronic and the molecular structure of orthorhombic metaboric acid have been investigated comprehensively by using ab initio Hartree Fock (HF) and Density Functional Theory DFT at the B3LYP level with 6-311++G(d, p) basis set. The conformational analysis was performed in detail for the first time as a function of both the φ (B1-O1-H) bond angle and the ψ (O6-B1-O1-H) dihedral angle. The results of calculated potential energy curves show that the molecule has two conformers (C-I and C-II Conformer) with minimum energies in a stable form. C-I conformer is a more stable form than C-II conformer. Linear and nonlinear optical properties of conformer C-I and C-II of the orthorhombic metaboric acid molecule are examined by the determination of the electric dipole moment μ, the polarizability α, and the hyperpolarizability β both methods. The optimized molecular structures of C-I and C-II conformer of the molecule belong to C3h and Cs symmetry, respectively. The dipole moment values for conformer C-II with Cs symmetry obtained using B3LYP/6-311++G(d, p) and HF/6-311++G(d, p) methods were found to be 2.95 and 3.07 Debye, Whereas, for C-I conformer with C3h symmetry, the values obtained using the same methods are found equal (0.0 Debye). Total energy distributions (TED) were calculated to find assignments of calculated vibration modes of both conformers by using VEDA 4f program. It was observed that there is a good agreement between the experimental data in the literature and the calculated structural parameters.

Experimental and theoretical insight into spectroscopic properties and bioactivity of 4-(4-formylbenzylidene)-2-phenyloxazol-5(4H)-one dye for future applications in biochemistry

The synthesized 4-(4-formylbenzylidene)-2-phenyloxazol-5(4H)-one was characterized by NMR and IR spectroscopy. The steady-state and time resolved measurements were applied to investigate its solvatochromism, determine dipole moments and elucidate its biological activity. Photophysical properties of the dye were studied in solvents of different polarities. Solute-solvent interactions were analyzed by means of multi-linear regression method using Catalán parameters whereas linear solvent correlation techniques like Lippert-Mataga, McRae and Bakhshiev polarity functions were used to evaluate the singlet excited state dipole moment. The achieved results indicate that the electronic absorption and fluorescence spectra of the oxazolone dye exhibit positive solvatochromism. Moreover, solvent polarizability is the major factor responsible for the observed red shift, thus the non-specific interactions mainly control the photophysical properties of the dye while the contribution of the specific interactions is weaker and mainly depend on solvent acidity. The rise in dipole moment of the dye occurs upon excitation due to the π-electron density redistribution. The spectroscopic measurements were supported by computational calculations including geometry optimization, spectral and physicochemical properties. The studies were also extended to evaluate bioactivity of the dye. The interaction between oxazolone dye and Concanavalin A was investigated by the fluorescence anisotropy method. The ion transporter action, especially sodium‑potassium pump function, and water transport in epithelial tissue were elucidated by the estimation of skin resistance.

Magnetic Dipole Moment Determination Using Near-Field Magnetic Gradient Tensor Data

Determination of the magnetic dipole moment of a spacecraft is a key issue for magnetic cleanliness and attitude control of various space scientific spacecraft. Two main methods, namely the multiple magnetic dipole modeling method and near-field analysis, have been used with good results inside a coil facility for prelaunch magnetic testing of a spacecraft. When field-canceling coil sets are unavailable, or coil feedback controls are inadequate to compensate for time-varying geomagnetic fields, determination of the magnetic signature of a spacecraft from measurements of field components is compromised. Therefore, we propose a magnetic dipole moment determination method using magnetic gradient tensor data without any coil facility, which is based on the fact that the time variation of the gradient tensor of the geomagnetic field is very small compared with that of field. We improve the near-field analysis method by expanding the magnetic gradient tensor in a series of spherical harmonics, obtain sets of near-field equations using Fourier analysis, and solve these equations to determine the dipole-moment components. The proposed tensor method can effectively suppress the interference from time variations of ambient magnetic fields. Simulations and experiments have been conducted to prove the validity, robustness, and accuracy of the tensor method.

Conductance and Configuration of Molecular Gold-Water-Gold Junctions under Electric Fields

Water molecules can mediate charge transfer in biological and chemical reactions by forming electronic coupling pathways. Understanding the mechanism requires a molecular-level electrical characterization of water. Here, we describe the measurement of single water molecular conductance at room temperature, characterize the structure of water molecules using infrared spectroscopy, and perform theoretical studies to assist in the interpretation of the experimental data. The study reveals two distinct states of water, corresponding to a parallel and perpendicular orientation of the molecules. Water molecules switch from parallel to perpendicular orientations on applying an electric field, producing switching from high to low conductance states, thus enabling the determination of single water molecular dipole moments. The work further shows that water-water interactions affect the atomic scale configuration and conductance of water molecules. These findings demonstrate the importance of the discrete nature of water molecules in electron transfer and set limits on water-mediated electron transfer rates.

Determination of the Electric Dipole Moment of a Molecule from Plane-Wave Density Functional Theory Calculations

The dipole moment calculated by using density functional theory (DFT) calculations varies, sometimes by a factor of 2, depending on the choice of the basis functions. We choose a plane-wave basis and calculate the electric dipole moment of a molecule by using the differential electron density with respect to the superimposed electron density of the free atoms, exploiting the cancellation of errors. Our results for a range of molecules show excellent agreement with experiments.

Determination of excited state dipole moments in solution via thermochromic methods

The method basically combines the existing ideas of excited state dipole moment determination via thermochromic fluorescence spectroscopy with the determination of the solvent cavity volume via concentration dependent density measurements of the solution densities at different weight fractions. Additionally, the determination of the cavity volume in dependence of the solvent temperature is included here, which provides a better accuracy of the excited state dipole moment determination. With this step two major sources of errors are eliminated: the use of the very imprecise Onsager radius and the assumption, that the cavity size is temperature independent.•Thermochromic absorption and fluorescence spectroscopy.•Cavity volume determination by density measurements.•Temperature dependent cavity volume determination.

A data-driven approach to determine dipole moments of diatomic molecules.

We present a data-driven approach for the prediction of the electric dipole moment of diatomic molecules, which is one of the most relevant molecular properties. In particular, we apply Gaussian process regression to a novel dataset to show that dipole moments of diatomic molecules can be learned, and hence predicted, with a relative error ⪅5%. The dataset contains the dipole moment of 162 diatomic molecules, the most exhaustive and unbiased dataset of dipole moments up to date. Our findings show that the dipole moment of diatomic molecules depends on atomic properties of the constituents atoms: electron affinity and ionization potential, as well as on (a feature related to) the first derivative of the electronic kinetic energy at the equilibrium distance.

Probing the anomalous electromagnetic dipole moments of the top quark in γp collision at the LHC, the HL-LHC and the HE-LHC

The determination of the electromagnetic dipole moments of the top quark is one of the most important goals of the top quark physics program in the collider experiments. For this reason, the top quark pair production to investigate the sensitivity on the electric and magnetic dipole moments of the top quark via the process pp→pγp→ptt¯X at the Large Hadron Collider (LHC), the High-Luminosity Large Hadron Collider (HL-LHC) and High-Energy Large Hadron Collider (HE-LHC) is discussed. We apply pure leptonic and semileptonic decays for top quark pair production in the final state. Moreover, we consider systematic uncertainties of 0,3% and 5%. The best limits obtained from the process pp→pγp→ptt¯X on the anomalous aA and aV couplings are |aA|=0.0200 and aV=[−0.9959;0.0003]. Thus, our results indicate that the process pp→pγp→ptt¯X is a very good perspective to probe the electric and magnetic dipole moments of the top quark at the HL-LHC and the HE-LHC.

Evaluation of Ground and Excited State Dipole Moments of 2(3)-tetra(tert-butylphenoxy)phthalocyaninato Zinc(II) from Solvatochromic Data

This article presents a semi-empirical determination of ground state dipole moment (mg) and excited state dipole moment (me) of 2(3)-tetra(tert-butylphenoxy)phthalocyaninato zinc(II) (ZnTBPc) using the solvatochromic shift method, which is based on the Onsager’s reaction field theory. A combined application of the Bakshiev’s equation and the Kawski-Chamma-Viallet’s equation was used to determine the ratio me/mg while the use of the molecular-microscopic solvent polarity parameter yielded the term Dm (me- mg). The dipole moment of ZnTBPc in its excited singlet state (me=4.46D) is more than twice as much as that in its ground state (mg=2.14D).These values suggest that the higher charge separation is greater in the excited state of ZnTBPc than in its ground state.

The Role of Computational Chemistry in the Experimental Determination of the Dipole Moment of Molecules in Solution.

The methods for the experimental determination of electric dipole moment of molecules in solution from measurements of dielectric permittivity and refractive index are traditionally based on the classical Onsager model. In this model the molecular solute is approximated as a simple polarizable point dipole inside a spherical or ellipsoidal cavity of a dielectric medium representing the solvent. However, the inadequacies of the model resulting from the assumption of a simple shape of the cavity, for the evaluation of the cavity field effect, and from the uncertainty of the polarizability of the molecular solute influences the results and hampers the comparison with the electric dipole moments computed from quantum chemical solvation models. In this article we propose a new method for the experimental determination of the electric dipole moment in solution in which information from the Polarizable Continuum Model calculations are used in place of the Onsager model. The new method overcomes the limitations of this latter model regarding both the cavity field effect and the polarizability of the molecular solutes, and thus allows a coherent comparison between experimental and computed dipole moments of solvated molecules. © 2019 Wiley Periodicals, Inc.

Thiaboranes on Both Sides of the Icosahedral Barrier: Retaining and Breaking the Barrier with Carbon Functionalities.

The concept of icosahedral barrier has been expanded from the chemistry of carbaboranes to the area of thiaboranes. Both representatives of this barrier, i. e., closo-1,2-C2 B10 H12 and closo-1-SB11 H11 , are similar in their electron distribution, which is dominated by positive charge in the midpoint of the C-C vector and on the sulfur atom with experimentally determined dipole moments of 4.50 D and 3.64 D, respectively. This is a driving force for their reactivity as exemplified by their reactions with different carbon functionalities. Icosahedral closo-1-SB11 H11 reacts both with an electron sextet containing carbon (in the form of N-heterocyclic carbenes), reported earlier, and with methyl iodide with an electron octet on the carbon. The latter reaction provides hexamethylated thiaborane on the basis of methylation so far unknown in this area of heteroborane chemistry. The computations of the heat of formation (ΔHf298 ) make it possible to estimate the height of the barrier as well as to propose closo-thiaboranes beyond the barrier. Eleven and twelve vertex thiaboranes with nido electron count are known experimentally for breaking the barrier. These computations also suggest that the larger nido-thiaboranes are promising candidates for the corresponding experimental availability, i. e., the ΔHf298 of a 13-vertex nido-thiaborane cluster has been computed to be more negative than that of the well-known nido-SB10 H11- cluster (-6.7 and -5.6 kcal mol-1 per vertex, respectively).

Theoretical design, synthesis and studies on the solvatochromic behaviour of low band gap phenylenevinylene based copolymers

A new series of low band gap phenylenevinylene based copolymers was designed by employing density functional theory in the periodic boundary condition using HSE06 exchange correlation functional using 6-31G basis set and synthesized via the Gilch polymerization. The theoretical band gap of the copolymers MD-CA-PPV, MD-FL-PPV, MD-PT-PPV and MD-AN-PPV were found to be 1.98, 2.07, 2.31 and 1.99 eV respectively using the DFT/HSE06/6-31G calculation and the optical band gap of 1.96, 2.03, 2.01 and 1.98 eV respectively, according to the onset edge of lower energy peak of the polymers in solution. The experimental results supported the theoretical prediction. Solvatochromic behaviour of the synthesized copolymers was studied thoroughly in toluene/acetonitrile mixtures of varying polarity at room temperature. The absorption spectrum of the PPV polymers was sensitive to solvent effects which showed bathochromic and hypsochromic shifts with increasing solvent polarity indicating that the transitions involved were π-π* and n-π*. The ground and excited state dipole moments were calculated using solvatochromic correlations. Onsager radius determined from ab initio calculation was used in the determination of dipole moments. The change in the dipole moment (Δμ) was calculated both from solvatochromic shift method and on the basis of microscopic empirical solvent polarity parameter (ETN) and values are compared. It was observed that the excited state dipole moment (µe) was larger than its ground state (µg) counterpart. This indicated that a substantial redistribution of the π-electron densities occurred in the more polar excited state for the selected phenylenevinylene polymers. The third-order nonlinear optical (NLO) properties of the copolymers, evaluated by Z-scan method with nanosecond laser beam at 532 nm, are reported. The nonlinear absorption coefficient of the copolymers were calculated to be 0.17 × 10−10, 2.06 × 10−10, 0.63 × 10−10 and 2.83 × 10−10 esu, respectively for MD-CA-PPV, MD-FL-PPV, MD-PT-PPV and MD-AN-PPV which certified that the polymers showed semiconductor properties.

Exploring the spectral features and quantum chemical computations of a novel biologically active heterocyclic class of compound 2MEFPBA dye: Experimental and theoretical approach

Abstract Here we report, experimental and theoretical determination of ground and excited state dipole moments of the class of heterocyclic compound namely 2-Methoxy-5-fluoro phenyl boronic acid (2MEFPBA) dye. Bathochromic shift with increasing solvent polarity is observed indicating π →π* transition due to intermolecular charge transfer interactions. The ground and excited state dipole moments are found to be parallel to each other. The molecular structure, Frontier molecular orbital (FMO), natural bond orbital (NBO) analysis and nonlinear optical (NLO) properties of 2MEFPBA have been investigated using the Density Functional Theory with B3LYP/6‒31 ++ g (d,p) basis set. Chemical reactivity and kinetic stability of 2MEFPBA are analyzed using FMO energy. Polarizability and hyperpolarizability computations are used to determine the NLO properties, whereas natural bond orbital (NBO) analysis showed the proton transfer within the selected donor-acceptor depicting large energy of stabilization for the compound under study.