Nuclear Polarizability Research Articles

Probing Excited-State Dynamics and Intramolecular Proton Transfer in 1-Acylaminoanthraquinones via the Intermolecular Solvent Response

The dynamics of a series of 1-acylaminoanthraquinones with varying degrees of excited-state intramolecular proton transfer are studied in acetonitrile and dichloromethane. Events are followed via changes in the third-order intermolecular Raman response as a function of time after resonant excitation of the chromophore. Compared to electronically resonant probes of the solute, measuring the ultrafast dynamics using the nonresonant solvent response offers a new and complementary perspective on the events that accompany excitation and proton transfer. Experimentally observed changes in the nuclear polarizability of the solvent follow dynamic changes in the solvent-solute interactions. Reorganization of the solvent in response to the significant changes in the intermolecular interactions upon proton transfer is found to play an important role in the reaction dynamics. With transfer of the proton taking place rapidly, the solvent controls the dynamics via the time-dependent evolution of the free energy surface, even on subpicosecond time scales. In addition, the solvent response probes the effects of intermolecular energy transfer as energy released during the reactive event is rapidly transferred to the local solvent environment and then dissipates to the bulk solvent on about a 10 ps time scale. A brief initial account of a portion of this work has appeared previously, J. Am. Chem. Soc. 2004, 126, 8620-8621.

Second-order vibronic reduction factors for orbital triplet Jahn–Teller systems in cubic andicosahedral symmetry

It is well-known that vibronic interactions can be modelled in terms of an effectiveHamiltonian incorporating first and second-order reduction factors (RFs), particularlywhen analysing the spectroscopic properties. Measurements and calculations of the RFs asa function of the strength of vibronic coupling are therefore of much interest. In this paper,we develop a new general method for determining second-order RFs (soRFs) from thestrength of the Jahn–Teller (JT) coupling for systems in which electron orbital degeneracyor pseudo-degeneracy exists. These include in particular the fullerene moleculeC60, pseudo-Jahn–Teller molecules and impurity centres in crystals. In order to calculate theimportant soRFs for intermediate to strong coupling, it is necessary to determinenon-Condon corrections to the strong coupling values obtained using the Franck–Condon(FC) approximation. This gives an additional contribution to the nuclear polarizability ofthe system, thus enabling the electrons to follow the nuclear vibrations. These non-Condoncorrections are derived using perturbation theory and are found to be inverselyproportional to the square of the JT energy. The validity of the approximation is firsttested in the cubic JT system due to its relative simplicity. It is found that the results arecloser to those obtained earlier by numerical methods than the analyticalFC values alone. Results are then presented that are applicable toC60− anions.

Solvation dynamics of coumarin 153 in several classes of ionic liquids: cation dependence of the ultrafast component

Time-resolved emission spectroscopy with 25 ps resolution is used to measure the dynamics of solvation of coumarin 153 in four ionic liquids (ILs), comprising three (imidazolium, ammonium, and phosphonium) cation classes. All four liquids possess similar electronic and nuclear polarizabilities. Solvation in the imidazolium ILs is biphasic, consisting of ultrafast (<5 ps) and slow (ns) components of roughly equal amplitudes near room temperature, whereas the ammonium and phosphonium ILs lack the ultrafast portion of the response. The slow solvation component displays kinetics typical of glass-forming liquids and tracks solution viscosity in a similar manner in all of the ILs.

Symmetry energy coefficients for asymmetric nuclear matter

Symmetry energy coefficients of asymmetric nuclear matter are investigated as the inverse of nuclear matter polarizabilities with two different approaches. Firstly a general calculation shows they may depend on the neutron-proton asymmetry itself. The choice of particular prescriptions for the density fluctuations lead to certain isospin (n-p asymmetry) dependences of the polarizabilities. Secondly, with Skyrme type interactions, the static limit of the dynamical polarizability is investigated corresponding to the inverse symmetry energy coefficient which assumes different values at different asymmetries (and densities and temperatures). The symmetry energy coefficient (in the isovector channel) is found to increase as n-p asymmetries increase. The spin symmetry energy coefficient is also briefly investigated.

Vibrational Effects on Molecular Properties in Large Molecules

We discuss an approach for calculating vibrational wave functions, eigenenergies and zero-point vibrational corrections to molecular properties. For simplicity the detailed theory is presented for a diatomic molecule, but the formulas for a general polyatomic molecule are also given. The approach has been implemented so as to allow vibrational corrections to be calculated for large molecules. We discuss recent applications of the model for calculating zero-point vibrational corrections to properties such as nuclear shielding constants, magnetizabilities, polarizabilities and optical rotation, and the use of this approach for obtaining accurate vibrational frequencies for bimolecular complexes.

The origin of electrooptical sensitivity of glassy materials: crystal motifs in glasses

The results of studying electrooptical Kerr sensitivity in heavy metal silicate and phosphate glasses and glass-ceramics are presented. A niobium–lithium-silicate glass demonstrating a record Kerr coefficient (266×10 −16 m/V 2) has been formed. Formation of the transparent glass-ceramics containing electrooptical sodium niobate microcrystals has been studied, and glass-ceramics demonstrating Kerr coefficients higher than 6000×10 −16 m/V 2 have been elaborated. On the base of the effective medium approximation, it is shown that the Kerr coefficient of these glass-ceramics depends on the volume fraction of sodium niobate microcrystals, v c as a linear function of v c(1− v c) −2 A conception of the origin of electrooptical sensitivity of glasses is proposed. This conception is based on the hypothesis that in glasses there exist regions with exactly crystalline ordering within 2–3 coordination spheres, with these regions having no phase boundaries. These regions are named the crystal motifs (CM). Due to the highly effective mechanism of nuclear polarizability of the electrooptical crystals, the motifs with the symmetry of such crystals are responsible for high permittivity and Kerr sensitivity of the glasses, and they play a role of pre-nuclei while electrooptical glass-ceramics are forming under glass heat treatment. It has been found that synthesized barium-titanate-silicate and niobium–lithium-phosphate glasses demonstrate extremely low Kerr coefficients, and they do not form transparent glass-ceramics with any electrooptical precipitates. This contradicts literature data and is explained by the difference in the conditions of glass synthesis, which are supposed to be responsible for the formation of proper CMs.

Shielding polarizabilities calculated at the coupled-cluster singles and doubles level augmented by a perturbative treatment of triple excitations

The nuclear magnetic shielding polarizabilities of N2, F2, CO, HF, HCl, HCN, HNC, and C2H2 have been computed at the coupled-cluster singles and doubles (CCSD) level augmented by a perturbative treatment of triple excitations [CCSD(T)] using gauge-including atomic orbitals and a mixed analytical-numerical approach based on the numerical differentiation of analytically evaluated shieldings. Extended basis sets have been employed to ensure results close to the basis set limit, and convergence of the electron-correlation treatment is investigated.

Finite field treatment of vibrational polarizabilities and hyperpolarizabilities: On the role of the Eckart conditions, their implementation, and their use in characterizing key vibrations

In the finite field (FF) treatment of vibrational polarizabilities and hyperpolarizabilities, the field-free Eckart conditions must be enforced in order to prevent molecular reorientation during geometry optimization. These conditions are implemented for the first time. Our procedure facilities identification of field-induced internal coordinates that make the major contribution to the vibrational properties. Using only two of these coordinates, quantitative accuracy for nuclear relaxation polarizabilities and hyperpolarizabilities is achieved in π-conjugated systems. From these two coordinates a single most efficient natural conjugation coordinate (NCC) can be extracted. The limitations of this one coordinate approach are discussed. It is shown that the Eckart conditions can lead to an isotope effect that is comparable to the isotope effect on zero-point vibrational averaging, but with a different mass-dependence.

Electric polarizability of nuclei from a longitudinal sum rule

The nuclear electric polarizability is theoretically analyzed using a sum rule derived from the longitudinal part of the forward Compton amplitude. Beyond the leading dipole contribution, this approach leads to the presence of potential-dependent terms that do not show up in previous analyses. The significance of these new contributions is illustrated by performing an explicit calculation for a proton-neutron system interacting via a separable potential.

ChemInform Abstract: Pictorial Representations of Molecular Response Tensors: Nuclear Shielding, Magnetizability, and Polarizability

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Nuclear polarizabilities and logarithmic sum rules

The electric polarizability and logarithmic mean-excitation energy are calculated for the deuteron using techniques introduced in atomic physics. These results are then used to improve limits on the atomic-deuterium frequency shift due to nuclear polarization in the unretarded dipole limit, as well as confirming previous results.

Nuclear polarization effects in spectra of multicharged ions

We evaluate the nuclear-polarization energy shifts for one-electron 208 82Pb and 238 92U ions. In contrast to previous calculations, the effect of nuclear polarizability is found to be essentially of minor significance for high-precision measurements of the Lamb shift in heavy multicharged ions. The calculations are carried out employing different numerical methods. We also provide a comparison of our numerical results with analytical estimates.

Accurate energy eigenvalues for enclosed hydrogen atom within spherical impenetrable boxes

AbstractWe study the hydrogen atom confined within spherical impenetrable walls. The potential in the box is the Coulombian potential and outside the box the potential is infinite. To compute the energy eigenvalues of the Schrödinger's equation, we use a method proposed few years ago by Campoy and Palma to solve free quantum systems. The energy eigenvalues are computed with great accuracy for different box sizes, in addition we also compute few position expectation values that are related with the hyperfine splitting, nuclear magnetic shielding, polarizability, and pressure. Our results are more accurate than the literature calculations. © 1995 John Wiley &amp; Sons, Inc.

Search for color van der Waals force in 208Pb+208Pb Mott scattering.

In a high precision experiment, Mott scattering of the [sup 208]Pb+[sup 108]Pb system was measured at [ital E][sub lab]=873.40 MeV and 1129.74 MeV with kinematic coincidences for angle pairs around [theta][sub lab]=30[degree], 60[degree] and [theta][sub lab]=45[degree], 45[degree]. The observed Mott oscillations exhibit an angular shift with respect to pure Mott scattering. A comparison with the angular shift produced by a color van der Waals force including nuclear polarizability, vacuum polarization, relativistic effects, and electronic screening provides a new upper limit for the strength of this force. Influence of atomic effects other than screening were identified for the first time.

Nuclear-structure correction to the Lamb shift.

In this paper the second-order nuclear structure correction to the energy of hydrogenlike systems is estimated and previous results are corrected. Both deuterium and hydrogen are considered. In the case of deuterium the correction is proportional to the nuclear polarizability and amounts to about -19 kHz for the 1S state. For hydrogen the resulting energy shift is about -60 Hz.

Structure and dynamics of water and aqueous solutions: The role of flexibility

The role molecular flexibility plays in the chemistry of bulk water and ionic solutions is evaluated using molecular dynamics simulations. For simplicity the flexible water model used here is the revised central force (CF) model of Stillinger and Rahman [J. Chem. Phys. 68, 666 (1977)]. A companion, rigid central force (RCF) model is invented to provide the most accurate average description of CF water. Discussion of the role of flexibility is divided into effects due to Coulombic and non-Coulombic parts of the potential energy. The Coulombic part provides the connection between flexibility and nuclear polarizability. A variety of thermodynamic and dynamical properties of the two models are compared. These include the static dielectric constant, orientational correlation functions, self-diffusion coefficient, pressure, intermolecular energy, and pair correlation functions. The effect of flexibility is greatest for dielectric properties, but in general it is found to be small. The dielectric constant of CF water is measured to be approximately 77, in good—perhaps fortuitous—agreement with the experimental value. A variety of ionic solution properties, including the free energy and dynamics of ionic association, are reported for model sodium chloride solutions at two concentrations. For these quantities also the effect of water flexibility is found to be small.

Effects of vacuum polarization on sub-coulomb 12C-12C scattering (l)

In order to investigate the effect of vacuum polarization on the sub-Coulomb interaction between hadrons, the relative differential cross section for elastic 12C-12C scattering at Elab = 4 MeV was measured with high precision at angles near 45°. Special care was taken to study various sources of systematic errors. The positions of the interference minima are determined to ±0.002°. The data are compared with theoretical calculations taking into account the contribution due to the Uehling potential and various other effects such as nuclear interaction, nuclear polarizability and electronic screening. The results of our experiment constitute a test of the vacuum polarization on the 7% level.

Vacuum polarization in sub-coulomb 12C-12C scattering (II)

In order to extract the effect of vacuum polarization from 12C-12C elastic scattering data, a detailed theoretical study of the low-energy Mott cross section is performed. It is shown that the contributions of nuclear interaction, Coulomb excitation, bremsstrahlung can be neglected, while radiative corrections and nuclear polarizability can be described by a small additional potential. Screening by atomic electrons is corrected by a screening function, which acts on all potentials. Relativistic effects are accounted for using the “Todorov equation”. In order to overcome numerical difficulties for very long range potentials a WKB approximation and a semiquantal approach are discussed and compared. The study shows that the first-order vacuum-polarization potential contributes most to the correction of the cross section. All other contributions are at least one order of magnitude smaller.

On the interplay between particle-hole and Δ-hole phonons

We show that the nuclear polarizability plays a very important role in establishing the magnitude of the Δ-hole polarization effect on the axial-vector coupling constant.

Low-energy theorems for nuclear polarizabilities

Low-energy theorems are derived for the nuclear polarizabilities of the photon scattering amplitude in a non-relativistic frame work. Center-of-mass recoil corrections are included in first order. We find, as a generalization of Friar's result, that E L contributions vanish to order k 2 L−2 for even L. For this result gauge conditions were crucial. To second order in the photon energy our results are equivalent to the low-energy theorem of Friar.