Showing papers on "Dipole published in 1982"
TL;DR: In this article, the relationships among various parameters describing the strength of optical transitions in atoms and molecules are reviewed and the application of these parameters to the description of the interaction between nearly monochromatic, directional light beams and atoms and molecule is given careful attention.
Abstract: The relationships among various parameters describing the strength of optical transitions in atoms and molecules are reviewed. The application of these parameters to the description of the interaction between nearly monochromatic, directional light beams and atoms and molecules is given careful attention. Common pitfalls in relating these parameters are pointed out.
600 citations
TL;DR: In this article, the adsorption system Pt(111)-CO has been investigated with LEED, thermal desorption and vibrat on spectroscopy using electron energy losses (EELS).
514 citations
TL;DR: Eisenberg et al. as mentioned in this paper examined the hydrophobic dipole moments in the known structures of nine globular proteins and found that the moments of neighbouring segments tend to point towards each other.
Abstract: The structure of a protein can be analysed in terms of what may be called the “hydrophobic moments” of (1) the entire molecule and (2) of the segments of secondary structure that make up the polypeptide chain. The zeroth moment is defined as the sum of the hydrophobicities of the amino-acid residues of the structure under consideration; it is the analogue of the net charge of a cluster of point charges. The first moment, or hydrophobic dipole moment, is the analogue of the electric dipole moment of a cluster of charges. Just as the electric dipole moment measures the asymmetry of the charge distribution, the hydrophobic dipole moment measures the amphiphilicity (asymmetry of hydrophobicity) of the structure. A large hydrophobic dipole moment indicates that a structure is predominantly hydrophobic on one side and predominantly hydrophilic on the other. A quadrupole hydrophobic moment may be similarly defined. It indicates whether a protein is more hydrophobic in its interior (as for a globular protein in aqueous solution) or at its surface (as for a membrane protein).The hydrophobic dipole moment is useful in two separate applications. The first, which we have discussed elsewhere [D. Eisenberg, R. M. Weiss and T. C. Terwilliger, Nature (London), 1982, 299, 371] relates the function and secondary structure of a region of protein structure to its amino-acid sequence. For example, sequences that form surface-seeking helices have large hydrophobic dipole moments. The second application is in the analysis of interactions of a segment or domain of a protein with neighbouring regions in the protein and with other parts of the environment. In this paper we examine the hydrophobic dipole moments in the known structures of nine globular proteins and find that the moments of neighbouring segments tend to point towards each other. This suggests that the hydrophobic dipole can serve as a simple and pictorial summary of some of the forces at work in the folding of proteins. We have also found that the interactions of some macromolecules with an apolar–polar interface can be conveniently described in terms of the hydrophobic moments of the molecule and a “hydrophobic field” which reflects the hydrophobicity of the environment.
428 citations
TL;DR: This model describes quantitatively the relative activities of those CDNP-lysine cytochromes c which are modified outside of the interaction domain and it allows correction of the activities of Those modified inside the domain, on the front surface of the molecule, for the change in dipole moment.
345 citations
IBM1
TL;DR: In this paper, the nonradiative damping of a dipole outside a metal surface is calculated using a realistic surface potential for the metal conduction electrons in contrast to most earlier studies.
Abstract: We present a calculation of the nonradiative damping of a dipole outside a metal surface. The calculation uses a realistic surface potential for the metal conduction electrons in contrast to most earlier studies. A simple experiment is suggested to test the theoretical predictions.
314 citations
TL;DR: In this paper, the decay of an excited molecule near a small metal sphere is considered from the viewpoint of electromagnetic theory, and the total decay rate of the emitting dipole is obtained by considering the two mechanisms through which energy is dissipated.
Abstract: The decay of an excited molecule near a small metal sphere is considered from the viewpoint of electromagnetic theory The total decay rate of the emitting dipole is obtained by considering the two mechanisms through which energy is dissipated One is the radiative loss, which is calculated from the Poynting vector, and the other is the nonradiative decay which is calculated from the Ohmic losses inside the sphere Numerical computations are performed for the case of a molecule near a small silver sphere, and the results are compared with those for a molecule near the planar boundary of a silver half‐space
283 citations
TL;DR: In this paper, an analysis has been made of all archeomagnetic intensity data for the past 50, 000 years and it has been shown that variations in the non-dipole field always remain in the same proportion to the dipole field irrespective of its magnitude.
Abstract: An analysis has been made of all archeomagnetic intensity data for the past 50, 000 years. There are 1, 175 results from different parts of the world covering the past 12, 000 years but these are heavily biased to the region of the northern hemisphere between 0° and 90°E (64% of data). The global means show a broad maximum about 6, 500 years B. P. There is no evidence from data older than 7, 000 years that a quasi-cyclic variation with period about 104 years exists.A careful analysis of 472 dipole moments covering the 2, 000 year period between 1000 A. D. and 1000 B. C. shows that they have a normal distribution with standard deviation of 19.7%. The estimate of the standard deviation of results within each 1, 000-year-interval for the past 10, 000 years is 21.2%. Analysis of the present field suggests a standard deviation of dipole moments of 17.5% would apply if the present field is representative of the past. This suggests the standard deviation due to experimental errors in archeomagnetic results is about 10%, a value that concurs with independent analysis. The ten 1, 000-year-mean dipole moments have mean 8.75×1022Am2 and estimated standard deviation 18.0% which may be attributed to dipole intensity fluctuations.Over the period 15, 000 to 50, 000 years B. P. the earth's dipole moment was low, the 14 results available having mean value 4.44×1022Am2 with estimated standard deviation 26.5%. This is precisely the scatter to be expected from a combination of dipole intensity fluctuations of 18.0% non-dipole variations of 17.5% and experimental errors of 10% as deduced for the past 10, 000 years. The conclusion therefore is that variations in the non-dipole field always remain in the same proportion to the dipole field irrespective of its magnitude. Furthermore, the time scale of changes in the earth's dipole moment must be very much longer than has previously been supposed and must be at least 105 years.
275 citations
TL;DR: In this article, the radiation pattern of an infinitesimal electric dipole was calculated for the case where the dipole is vertically located on the plane interface of two dielectric half spaces.
Abstract: The radiation pattern of an infinitesimal electric dipole is calculated for the case where the dipole is vertically located on the plane interface of two dielectric half spaces and for the case where the dipole is lying horizontally along the interface. For the vertical case, it is found that the radiation pattern has nulls at the interface and along the dipole axis. For the horizontal case, it is found that the pattern has a null at the interface; that the pattern in the upper half space, whose index of refraction is taken to be less than that of the lower half space, has a single lobe whose maximum is normal to the interface; and that in the lower half space, in the plane normal to the interface and containing the dipole, the pattern has three lobes, whereas in the plane normal to the interface and normally bisecting the dipole, the pattern has two maxima located symmetrically about a minimum. Interpretation of these results in terms of the Cerenkov effect is given.
207 citations
TL;DR: In this article, the polarized X-ray absorption cross section of the ls → 3d transition in a square planar CuCl2−4 complex has been measured with respect to rotation about an axis normal to the CuCl4.
204 citations
TL;DR: In this article, the charge density in α-Al2O3 has been refined with respect to X-ray structure factors [complete spheres for both Mo Kα and Ag Kα radiations with (sin θ/λ)max = 1.19 and 1.495 A-1 respectively] and electric-field gradient tensors at both atomic sites.
Abstract: The charge density in α-Al2O3 has been refined with respect to X-ray structure factors [complete spheres for both Mo Kα and Ag Kα radiations with (sin θ/λ)max = 1.19 and 1.495 A-1 respectively] and electric-field gradient tensors at both atomic sites, using Hirshfeld- type deformation functions. Atomic charges from a κ refinement are + 1.32 (5) for Al and -0.88 (8) e for O. The charge distribution of O is polarized towards the four Al neighbours, and metal-metal bonds are clearly absent. Quadrupole coupling constants and asymmetry parameters of the field-gradient tensors cannot be determined from the structure factors. They define the quadrupolar deformations near the atomic centers, and the X-ray data define the charge density between the atoms. The orientational parameters of the tensors and the signs of their largest eigenvalues can be qualitatively retrieved from the X-ray data. The refinement of anisotropic secondary-extinction parameters may, however, destroy this information. Refinement with respect to the field gradients affects mainly the quadrupolar deformation terms, and has little influence on the X-ray scale factor (i.e. monopolar terms) and computed electrostatic fields (i.e. dipolar terms). Properties of the charge density with different angular symmetries are thus only weakly correlated.
189 citations
TL;DR: In this article, two molecular dynamics simulations of 216 molecules interacting by the ST2 water potential were carried out, where the reaction field method was applied and the influence of long range interactions was carefully studied.
Abstract: Two molecular dynamics simulations of 216 molecules interacting by the ST2 water potential were carried out. Apart from technical improvements, the first simulation was identical to that reported by Stillinger and Rahman [4]. In the second, however, the reaction field method was applied and the influence of long range interactions was carefully studied. 7500 time steps (= 7·5 ps) were generated. The temperature given by the average kinetic energy was 120°C. The atom-atom pair correlation functions and the average dipole energy are rather insensitive to the reaction field. The average cosine between two molecular dipoles, however, is strongly influenced and corresponding curves are of different sign in the second and third coordination shell. For the integral of the average cosine, namely the Kirkwood g-factor g K, the situation is even worse : Large errors occur if the long range interactions are neglected. On the other hand, a convergence of g K was achieved by the inclusion of the reaction field. The pr...
TL;DR: The metal surface selection rule as discussed by the authors predicts that some infrared absorption bands should be absent from the spectra of molecules adsorbed on metal particles, and it predicts that those bands corresponding to molecular vibrations with an oscillating dipole moment parallel to the surface should be suppressed.
TL;DR: In this paper, a third-order zonal harmonic model fitted to Voyager 1 and 2 observations is found to be capable of predicting the magnetic field characteristics at one encounter based on those observed at another, unlike models including dipole and quadrupole terms.
Abstract: An analysis of the magnetic field of Saturn is presented which takes into account both the Voyager 1 and 2 vector magnetic field observations. The analysis is based on the traditional spherical harmonic expansion of a scale potential to derive the magnetic field within 8 Saturn radii. A third-order zonal harmonic model fitted to Voyager 1 and 2 observations is found to be capable of predicting the magnetic field characteristics at one encounter based on those observed at another, unlike models including dipole and quadrupole terms only. The third-order model is noted to lead to significantly enhanced polar surface field intensities with respect to dipole models, and probably represents the axisymmetric part of a complex dynamo field.
TL;DR: In this article, the best available intensity data for some hundred or so molecules and evaluated their vibrational polarizabilities were collected, and the probable errors of the final numbers were given.
Abstract: An often overlooked, but nonetheless important, contribution to molecular dipole polarizabilities is that which comes from molecular vibration. This contribution, which was formerly called the atomic polarization, may be related to the intensities of the infrared‐active bands. In this paper we have collected the best available intensity data for some hundred or so molecules and evaluated their vibrational polarizabilities. We have also given estimates of the probable errors of the final numbers.
TL;DR: Rotation of cells in an alternating electric field is described theoretically by interaction between induced dipoles is adjacent cells and the optimum frequency range for rotation is related to the relaxation of the polarization process in the cell.
Abstract: Protoplasts of Avena sativa rotate in an alternating electric field provided that at least two cells are located close to each other. An optimum frequency range (20 to 30 kHz) exists where rotation of all cells exposed to the field is observed. Below and above this frequency range, rotation of some cells is only occasionally observed. The angular velocity of rotation depends on the square of the electric field strength. At field strengths above the value leading to electrical breakdown of the cell membrane, rotation is no longer observed due to deterioration of the cells. The absolute value of the angular velocity of rotation at a given field strength depends on the arrangement of the cells in the electric field. A maximum value is obtained if the angle between the field direction and the line connecting the two cells is 45 degrees. With increasing distance between the two cells the rotation speed decreases. Furthermore, if two cells of different radii are positioned close to each other the cell with the smaller radius will rotate with a higher speed than the larger one. Rotation of cells in an alternating electric field is described theoretically by interaction between induced dipoles in adjacent cells. The optimum frequency range for rotation is related to the relaxation of the polarization process in the cell. The quadratic dependence of the angular velocity of rotation on the field strength results from the fact that the torque is the product of the external field and the induced dipole moment which is itself proportional to the external field. The theoretical and experimental results may be relevant for cyclosis (rotational streaming of cytoplasm) in living cells.
TL;DR: In this article, a number of one-electron properties of single isolated urea molecules are considered by means of a finite-field perturbated LCAO Hartree-Fock model implemented at both semi-empirical (INDO) and ab initio levels of approximation with different basis set extensions.
Abstract: The validity of simpler additive models, accounting for nonlinear optical properties of van der Waals crystals in terms of independent molecular contributions is questionable in the case of more associated molecular structures such as examplified by the hydrogen‐bonded crystal lattice of urea. A number of one‐electron properties of single isolated urea molecules are first considered by means of a finite‐field perturbated LCAO Hartree–Fock model implemented at both semiempirical (INDO) and ab initio levels of approximation with different basis set extensions. Charge distribution, dipole (μ), multipoles, linear (α), quadratic (β), and cubic hyperpolarizabilities γ are computed and analyzed. The α tensor is shown to be quasi‐isotropic in the molecular plane while the β tensor exhibits a stronger anisotropy and a prevailing βzzz coefficient (z is the molecular symmetry axis). The negative value of the product βzzzμz is interpreted by a decrease of the dominant excited state dipole as compared to that of the g...
TL;DR: In this article, it was shown that when a monochromatic laser couples a single ground level to two closely spaced excited levels, the system can be driven into a state in which quantum interference prevents any fluorescence from the excited levels regardless of the intensity of the exciting field.
Abstract: It is shown that when a monochromatic laser couples a single atomic ground level to two closely spaced excited levels the system can be driven into a state in which quantum interference prevents any fluorescence from the excited levels, regardless of the intensity of the exciting field. This steady-state interference occurs only at a particular excitation frequency which depends on the separation of the excited states and the relative size of the two transition dipole matrix elements. The results are derived from the density matrix equations of motion. It is shown that a correct description of the effect requires the inclusion of generalised Einstein A coefficients which are usually neglected in phenomenological damping theories. A dressed-state analysis is introduced to simplify the generalisation to atoms having more complex manifolds of excited states. Analogous interferences in multiphoton absorption and ionisation are also discussed briefly.
TL;DR: In this paper, a new mechanism was considered due to which the neutron electric dipole moment D n arises in the Kobayashi-Maskawa model, leading to the estimate D n ∼ 2 × 10 −32 e cm, by two orders of magnitude larger than contributions considered previously.
TL;DR: The theoretical basis for using dipole moment as a free-energy related parameter in studying drug-receptor interaction and quantitative structure-activity relationship (QSAR) is presented and examples in the literature of using dipoles moment in QSAR studies are presented.
TL;DR: In this article, the authors compared the Tauc model with the model first introduced by Tauc for optical transitions, with momentum conservation relaxed, between the valence (occupied) and conduction (unoccupied) bands of an amorphous semiconductor.
TL;DR: The observed interaction orientation frequencies demonstrate that these multipolar electron distributions, when occurring at the short distances encountered in densely packed protein molecules, are significant determinants of internal packing geometries.
Abstract: The atomic environments of 170 phenylalanine-residue aromatic rings from 28 protein crystal structures are transformed into a common orientation and combined to calculate an average three-dimensional environment. The spatial distribution of atom types in this environment reveals a preferred interaction between oxygen atoms and the edge of the planar aromatic rings. From the difference in frequency of interaction of oxygen atoms with the edge and the top of the ring, an apparent net free energy difference of interaction favoring the edge of the ring is estimated to be about -1 kcal/mol (1 cal = 4.184 J). Ab initio quantum mechanical calculations, performed on a model consisting of benzene and formamide, indicate that the observed geometry is stabilized by a favorable enthalpic interaction. Although benzene rings are considered to be nonpolar, the electron distribution is a complex multipole with no net dipole moment. The observed interaction orientation frequencies demonstrate that these multipolar electron distributions, when occurring at the short distances encountered in densely packed protein molecules, are significant determinants of internal packing geometries.
TL;DR: In this paper, absolute total and differential rotational and rotational-vibrational cross sections have been measured for N2 (weak quadrupole), CO (weak dipole), and H2O (strong dipole).
Abstract: Absolute total and differential rotational and rotational-vibrational cross sections have been measured for N2 (weak quadrupole), CO (weak dipole), and H2O (strong dipole). In the beam experiments, the range of collision energies of the electrons was chosen between 0.5 and 6 eV, and the range of scattering angles from 15 to 105 degrees was covered. The overall energy inhomogeneity of the electron spectrometer was between 10 and 18 meV FWHM, depending on the experiment. Direct and resonant rotational excitation has been measured. In the case of N2 the rotational branches with Delta J=0, +or-2, +or-4 have been fitted to energy-loss spectra and for each branch a cross section is given. The authors have proceeded similarly in the case of CO (for dipole excitation Delta J=0, +or-1, for excitation via the 2 Pi resonance Delta J=0, +or-1, ..., +or-4) and in the case of H2O ( Delta J=0, +or-1). For N2 and CO the results are compared with calculated angular dependences. Finally, the cross sections are listed according to the different types of interaction potentials and interaction mechanisms.
TL;DR: The results clearly showed the dominant role played by the axial component of the potential field even at a considerable distance from the heart, as well as the features of the measured potential fields, which could not be interpreted on the basis of the solid angle theory.
Abstract: The potential distribution in a homogeneous, cylindrical volume conductor surrounding an isolated paced dog heart was first measured and then calculated by using a mathematical model that stimulates an anisotropic excitation wavefront spreading through the heart muscle. The study was performed with a view to establish to what extent the anisotropy of cardiac generators affects the potential field in the extra-cardiac conducting media at a great distance from the heart. The model considers an oblique dipole layer on the wavefront which, assuming axial symmetry of the electrical properties of the fibers, can be viewed as the superposition of an axial and transverse dipole layer. These layers are, respectively, parallel and perpendicular to the local fiber due to such an oblique distribution is also equivalent to the sum of the potentials generated, respectively, by a normal and an axial dipole layer. In this form, the model generalizes the classical, uniform double layer model, upon which the solid angle theory is based, by adding to it an axial component. The features of the measured potential fields, which could not be interpreted on the basis of the solid angle theory, were satisfactorily reproduced by the model, at least on a qualitative basis. The results clearly showed the dominant role played by the axial component of the potential field even at a considerable distance from the heart.
TL;DR: In this article, it was shown numerically that this mechanism may account for the largest contribution to the two-photon cross section in polar molecules, if the dipole moment strongly alters with excitation.
Abstract: Two‐photon transitions may proceed via a mechanism not involving virtually excited intermediate states. For some examples, it is shown numerically that this mechanism may account for the largest contribution to the two‐photon cross section in polar molecules, if the dipole moment strongly alters with excitation. Possible consequences for the two‐photon detection of ’’forbidden’’ states in polar polyene systems are discussed.
TL;DR: By means of a statistical experiment and using estimates of the variance of the recorded evoked fields, it is shown that the model suggested is adequate to describe the experimental data and that the overall confidence of the extracted dipole parameters can be estimated.
Abstract: Auditory evoked cortical magnetic fields are recorded from human subjects by means of a SQUID gradiometer. The spatial and temporal distributions of the averaged evoked fields normal to the surface of the skull are measured from both hemispheres in response to contra- and ipsilateral 1 kHz stimulation. The evoked magnetic response can be separated into a dominant and a 'residual' signal and the former is analysed with a particular source model consisting of a single equivalent current dipole in each hemisphere. We find that the equivalent current dipoles are located near the superior surface of the temporal lobes approximately 20 mm below the surface of the skull. The dipoles are oriented in the superior-inferior direction. In the left hemisphere the dipole is located approximately 14 mm posterior to that in the right hemisphere, but otherwise no hemisphere/ear difference in dipole location or orientation is found. The strength of the dipole in the left hemisphere is found to be twice as great as that in the right hemisphere when stimulating the right ear, whereas no difference is found when stimulating the left ear. The strength of the dipole is greater in response to contralateral than ipsilateral stimulation. By means of a statistical experiment and using estimates of the variance of the recorded evoked fields we show that the model suggested is adequate to describe the experimental data and that the overall confidence of the extracted dipole parameters can be estimated.
TL;DR: In this article, the angular distribution of photoelectrons with defined spin polarization ejected from oriented optically active molecules is derived and shown to have a circular dichroism in the electric dipole approximation.
TL;DR: In this paper, bipolar magnetic field effects have been detected in the NMR spectra of coronene and methyl pyropheophorbide in liquid solution, which arise from the partial molecular alignment induced by the magnetic field.
15 May 1982
TL;DR: In this article, the authors presented a reasonably general discussion of the difficulties associated with obtaining reliable results for C 6 by using Pade approximant bounding methods, and provided pseudo-DOSD representations of the recommended DOSDs which allow the efficient accurate evaluation of the dispersion energy coefficients C 6 for the interaction of CO or CO 2 with other atoms and molecules.
Abstract: Globally reliable dipole oscillator strength distributions (DOSDs) have been constructed for ground state CO and CO 2 molecules; the DOSD for CO corresponds to photon energies greater than the electronic absorption threshold while that for CO 2 includes the infrared part of the spectra as well. The recommended DOSDs are used to evaluate the isotropic dipole—dipole dispersion energies for the COCO, COCO2 and CO2CO2 interactions as well as the molar refractivities, as a function of wavelength, and the dipole sums, S k , k = 2(−1) -4, -6, -8, -10, for the two molecules. Pseudo-DOSD representations of the recommended DOSDs are provided which allow the efficient accurate evaluation of the dispersion energy coefficients C 6 for the interaction of CO or CO 2 with a variety of other atoms and molecules. Previous results for C 6 are found to be in disagreement with our recommended results for interactions involving CO 2 . The results of this paper are used to give a reasonably general discussion of the difficulties associated with obtaining reliable results for C 6 by using Pade approximant bounding methods.
TL;DR: In this paper, first-order (identical to coupled Hartree-Fock) and second-order polarization propagator calculations of the dynamic dipole polarizability tensor for the CO, N 2, HCl and Cl 2 molecules were performed.