Range relaxation

The first of three integral forms of the quantum mechanical variational principle is described and a method introduced for the simultaneous optimisation of the whole of a molecular energy curve, or surface, generated for some adiabatic change. Dimensionless parameters in the wavefunction are expressed as functions of the coordinates and the integral of the energy over the whole surface is minimised with respect to variations in these functions. An integral form of the Virial Theorem is proposed as a test that the wavefunction is in scale for the whole range. A preliminary application is made to the H ⁺₂ , H₂ and He₂ systems.

     

Anomalously slow solvent structural relaxation accompanying high-energy rotational relaxation

Experimental and theoretical work on the relaxation of rapidly rotating solutes in liquids have pointed out a number of striking features. Even in rapidly relaxing solvents, the relaxation proceeds quite slowly, exhibiting a manifestly nonlinear response that depends explicitly on the initial rotational energy. In this paper, we show how the long-time behavior, in particular, stems from a strong coupling of solute orientation to local solvent geometry. This coupling creates a rotational friction that decreases sharply with rotational energy, allowing for the protracted survival of not only high-angular-momentum rotational states but the cavity-like low-friction solvent geometries. We show, further, that the slow dynamics is dynamically heterogeneous. The distribution of excited rotors is marked by a distinct population of slowly relaxing hot rotational states. This population can be traced directly to the small subset of liquid configurations that happen to have low rotational friction values at the instant at which the rapid rotation started, indicating an unusual failure of the normally chaotic environment of a liquid to randomize initial conditions.     

Creep relaxation and stress relaxation of PS-HI/SEBS blends

For the selection of the polymer materials and polymer blends for various fields of applications the stability of material under constant deformation and constant load are very important. In this paper, the copolymers high-impact polystyrene, PS-HI, styrene-ethylene/buthylene-styrene block copolymer, SEBS, and their blends PS-HI/SEBS were investigated. The investigations were done by DMA analysis. The secondary viscoelastic functions, creep, creep modulus, stress and flexural relaxation modulus were investigated in creep and stress relaxation experiment at temperatures 25, 35, 45, 55 and 65°C during 1 h. The master curves were created by time-temperature correspondence principle, TTC. The correlation of the secondary viscoelastic functions with time, temperature and content of the hard, PS, phase was discussed.     

Compression stress relaxation

The requirements of apparatus to measure stress relaxation of rubbers in compression are outlined. Apparatus available commercially are described, in particular a universal semi-automatic force measuring head and jigs which accept button test pieces and have no sliding bearings to introduce friction.     

Coexistence of magnetization relaxation and dielectric relaxation in a single-chain magnet

A novel single-chain magnet, [MnIII3O(Meppz)3(EtOH)4(OAc)] (1), has been successfully synthesized from a secondary building block [MnIII3O(Meppz)3(EtOH)5Cl] (2) with an S = 1 ground state. SCM 1 exhibits both magnetization relaxation and dielectric relaxation properties.     

Vibrational relaxation carbon tetrachloride

By use of spontaneous Brillouin scattering, the vibrational relaxation of carbon tetrachloride was determined as a function of temperature. Comparison of experimental results with theoretical predictions leads to the conclusion that there is a simultaneous relaxation of three internal modes.     

Dielectric relaxation of polydimethylsiloxane

Dielectric studies were performed on crystallized and amorphous polydimethylsiloxane which had been characterized by differential thermal analysis and polarized light microscopy. The crystallized specimen displayed one relaxation near 160 K at 1 kHz while the amorphous specimen showed absorption peaks at 155 and 165 K. For the latter material the high-temperature peak was not due to a true relaxation but resulted from crystal nucleation at 160 K and the subsequent growth of spherulites. The low-temperature peak at 155 K resulted from the relaxation associated with the glass transition. A sharp decrease of dielectric constant was observed for both specimens at the melting point (235 K). For the dielectric relaxation associated with the glass transition in crystallized specimens, the values of the dispersion amplitude, the apparent activation energy at 160 K, and the half-width of the absorption curve are 0.43 and 29 kcal/mole, and 5.6 decades, respectively, which are in marked contrast to the corresponding values of 0.82, 18, and 2.2 for amorphous specimens.     

Electron-pair density relaxation holes

The electron-pair density relaxation hole has been defined as the electron-pair density of the real molecule minus the electron-pair density of a reference system consisting of overlapping, spherically averaged, undeformed atoms, positioned at the molecular nuclear coordinates. We have shown how it can be calculated from one- and two-electron reduced density matrices expanded in a Gaussian type basis set. Analysis of the calculated radial electron-pair density holes, from full configuration interaction one- and two-electron reduce density matrices, for the ground states of the hydrogen molecule, the helium dimer and the lithium and beryllium hydrides reveal that the different types of bonding interactions yield distinctively visually recognizable different topological patterns of the electron-pair density relaxation hole.     

Anisotropy of spin-lattice relaxation

The anisotropy is determined for the spin-lattice relaxation time in the presence of a strong magnetic field in crystals of the NaCl type due to the components of a generalized hyperfine-interaction spin-Hamiltonian. It is shown that taking into account components other than the contact, dipole, and quadrupole interactions leads to an additional angular dependence for the relaxation time and also to additional relaxation transitions.     

Cross relaxation effects on the longitudinal relaxation rate of water in protein solutions

Non-selective and selective longitudinal relaxation rates were measured for water protons in protein solutions. The perturbations on water spin-lattice relaxation from cross relaxation between water and protein protons were shown to be significant at low temperature and small isotopic dilution.     

Shear stress relaxation in liquids

We show that at high densities, as the system size decreases, liquid becomes able to permanently sustain increasing internal shear stress after a constant deformation, although the other characteristic liquid properties, such as the pair distribution function and diffusion coefficient do not change under strain. The system size necessary for observation of this effect increases with the decrease in temperature, and it is stronger in pair potentials with steeper repulsive part. We relate this result to the size of the "cooperatively rearranging regions" of the Adam-Gibbs theory of glass transition.     

Radiative relaxation in synthetic pheomelanin

We report a detailed photoluminescence study of cysteinyldopa-melanin (CDM), the synthetic analogue of pheomelanin. Emission spectra are shown to be a far more sensitive probe of CDM's spectroscopic behavior than are absorption spectra. Although CDM and dopa-melanin (DM, the synthetic analogue of eumelanin) have very similar absorption spectra, we find that they have very different excitation and emission characteristics; CDM has two distinct photoluminescence peaks that do not shift with excitation wavelength. Additionally, our data suggest that the radiative quantum yield of CDM is excitation energy dependent, an unusual property among biomolecules that is indicative of a chemically disordered system. Finally, we find that the radiative quantum yield for CDM is approximately 0.2%, twice that of DM, although still extremely low. This means that 99.8% of the energy absorbed by CDM is dissipated via nonradiative pathways, consistent with its role as a pigmentary photoprotectant.     

Nuclear magnetic resonance relaxation titration

Summary Quantitative determination of the concentration of paramagnetic ions in aqueous solutions is performed by NMR relaxation titration. By measurement of the nuclear spin-lattice relaxation time T ₁ or the nuclear spin-spin relaxation time T₂ redox titrations and complexometric determinations of the concentration of paramagnetic ions are possible. Also the precipitation of ions from the solution can be followed by this method. The use of a magnetic indicator in this analytical method is shown. The sensitivity of the method goes down to concentrations as low as 10^–3 M. The accuracy of NMR relaxation titration is better than 1%. A number of applications of the method are given.

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Kernmagnetische Relaxationstitration

Zusammenfassung Quantitative Bestimmungen von paramagnetischen Ionen in wäßrigen Lösungen können mit Hilfe der kernmagnetischen Relaxationstitration durchgeführt werden. Durch Messung der Kernspin-Gitter-Relaxationszeit T ₁ oder der Kernspin-Kernspin-Relaxationszeit T ₂ als Funktion der Ionenkonzentration sind Redoxtitrationen oder komplexometrische Titrationen möglich. Der quantitative Ablauf von Fällungen kann ebenfalls verfolgt werden. Die Verwendung von magnetischen Indicatoren bei der Relaxationstitration wird beschrieben. Bestimmungen von Ionenkonzentrationen bis herab zu 10^–3 M Lösungen sind z.Z. möglich. Die Methode erlaubt eine Genauigkeit der Konzentrationsbestimmung von 1% und besser. Die Anwendung der Methode wird an einer Reihe von Beispielen gezeigt.

     

Rotational relaxation of polar molecules

The method of obtaining rotational energy relaxation times from experimental thermal conductivities using the Wang Chang-Uhlenbeck theory of transport coefficient for polyatomic gases is considered. For polar gases the method turns out to be useful only if serious calculations of the inelastic collisions involved are performed. Using a semiclassical, partly statistical collision treatment the results for the rotational energy relaxation numbers for halogen hydrides taking dipole-dipole, dipole-quadrupole and quadrupole-quadrupole interactions into account are presented. It is characteristic for the results that hardly any temperature dependence or isotope effects are observed, a behaviour different from earlier investigations.     

Non-markovian effects in dielectric relaxation

A generalized Nee—Zwanzig equation is proposed to describe both low and high frequency dielectric relaxation. It is shown that the inertial effect is closely related to the non-markovian character of the differential equation governing the time evolution of the dipole—dipole autocorrelation function. Comparison with experimental results is given.     

Non-equilibrium shear relaxation in liquids

A theory for non-equilibrium shear relaxation in liquids at low frequencies is presented. It is based on molecular considerations used in theories of low frequency depolarized light scattering.The results for the complex shear impedance contain terms in addition to those obtained by the phenomenological relaxation theory.