Infrared intensity analysis of CH2Cl2 and CD2Cl2 in vapour and liquid states

In the infrared spectra of molecules with more than one C-H bond the symmetric and antisymmetric stretching bonds often overlap, causing uncertainty in the intensity analysis. For CH₂Cl₂ and CD₂Cl₂ in the vapour state, the two bands overlap to such an extent that Straley who takes it as one band attributes it to antisymmetric stretching while Saekiet al assign it to the symmetric stretching. Following the method of analysis initiated in this laboratory, we have solved this problem by ultimately obtaining intensities separately forA ₁ andB ₂ species. The band is mostly due to the symmetric stretching, 0.06 out of the total of 0.31 contributing toB ₂. Thus, this gives a method of separating the intensities of bands which are highly overlapping. Presented at the Symposium on Crystallography and Crystal Physics, Osmania University, Hyderabad held on 5–7, December 1977.     

Relaxation phenomena of polar non-polar liquid mixtures under low and high frequency electric field

Simultaneous calculation of the dipole moment μ_j and the relaxation time τ_j of a certain number of non-spherical rigid aliphatic polar liquid molecules (j) in non-polar solvents (i) under 9.8 GHz electric field is possible from real ε′_ij and imaginary ε″_ij parts of the complex relative permittivity ε*_ij. The low frequency and infinite frequency permittivities ε_0ij and ε_∞ij measured by Purohitet al [1,2] and Srivastava and Srivastava [3] at 25, 35 and 30°C respectively are used to obtain static μ_s. The ratio of the individual slopes of imaginary σ″_ij and real σ′_ij parts of high frequency (hf) complex conductivity σ*_ij with weight fractionsw _jatw _j → 0 and the slopes of σ″_ij— σ′_ij curves for differentw _js [4] are employed to obtain τ_js. The former method is better in comparison to the existing one as it eliminates polar-polar interaction. The hf μ_js in Coulomb metre (C m) when compared with static and reported μs indicate that μ_s s favour the monomer formations which combine to form dimers in the hf electric field. The comparison among μs shows that a part of the molecule is rotating under X-band electric field [5]. The theoretical μ_theos from available bond angles and bond moments of the substituent polar groups attached to the parent molecules differ from the measured μ_js and μs to establish the possible existence of mesomeric, inductive and electromeric effects in polar liquid molecules.     

Dielectric investigation of relaxation in some heterocyclic compounds

The dielectric relaxation mechanism in five heterocyclic compounds in dilute solutions using microwave technique is reported. Measurements have been made at different temperatures in order to calculate dipole moments and free energies of activation for the process of dipole orientation and viscous flow. It has been observed that the relaxation time is very closely related with the molecular parameters, such as size, shape and nature of the solute molecule.     

Influence of fluorination and chain length on the static dielectric properties of nematogenic bi-cyclohexyl phenyl derivatives

Effects of fluorination and chain length of six bi-cyclohexyl phenyl compounds (3ccp-f, 3ccp-ff, 3ccp-fff, 5ccp-f, 5ccp-ff, 5ccp-fff) on their physical properties have been investigated. All the compounds exhibit nematic phase over a wide range of temperatures. Molecular mechanics calculation reveals that dipole moments of the molecules increases (1.93D to 3.37D) with fluorination in both propyl- and pentyl-based systems; increment in f to ff derivatives is more than in ff to fff derivatives. However, no change in dipole moment is observed with increased chain length. In the nematic phase, average value of dielectric constant (?_avg) is less than the extrapolated values of ?_iso in isotropic phase. Increased fluorination also decreases splay elastic constant, and thus faster response is expected in triply fluorinated compounds.     

Relaxation of protons by radicals in rotationally immobilized proteins

Proton spin-lattice relaxation by paramagnetic centers may be dramatically enhanced if the paramagnetic center is rotationally immobilized in the magnetic field. The details of the relaxation mechanism are different from those appropriate to solutions of paramagnetic relaxation agents. We report here large enhancements in the proton spin-lattice relaxation rate constants associated with organic radicals when the radical system is rigidly connected with a rotationally immobilized macromolecular matrix such as a dry protein or a cross-linked protein gel. The paramagnetic contribution to the protein-proton population is direct and distributed internally among the protein protons by efficient spin diffusion. In the case of a cross-linked-protein gel, the paramagnetic effects are carried to the water spins indirectly by chemical exchange mechanisms involving water molecule exchange with rare long-lived water molecule binding sites on the immobilized protein and proton exchange. The dramatic increase in the efficiency of spin relaxation by organic radicals compared with metal systems at low magnetic field strengths results because the electron relaxation time of the radical is orders of magnitude larger than that for metal systems. This gain in relaxation efficiency provides completely new opportunities for the design of spin-lattice relaxation based contrast agents in magnetic imaging and also provides new ways to examine intramolecular protein dynamics.     

Relaxation dispersion in MRI induced by fictitious magnetic fields

A new method entitled Relaxation Along a Fictitious Field (RAFF) was recently introduced for investigating relaxations in rotating frames of rank ≥ 2. RAFF generates a fictitious field (E) by applying frequency-swept pulses with sine and cosine amplitude and frequency modulation operating in a sub-adiabatic regime. In the present work, MRI contrast is created by varying the orientation of E, i.e. the angle ε between E and the z″ axis of the second rotating frame. When ε > 45°, the amplitude of the fictitious field E generated during RAFF is significantly larger than the RF field amplitude used for transmitting the sine/cosine pulses. Relaxation during RAFF was investigated using an invariant-trajectory approach and the Bloch-McConnell formalism. Dipole-dipole interactions between identical (like) spins and anisochronous exchange (e.g., exchange between spins with different chemical shifts) in the fast exchange regime were considered. Experimental verifications were performed in vivo in human and mouse brain. Theoretical and experimental results demonstrated that changes in ε induced a dispersion of the relaxation rate constants. The fastest relaxation was achieved at ε ≈ 56°, where the averaged contributions from transverse components during the pulse are maximal and the contribution from longitudinal components are minimal. RAFF relaxation dispersion was compared with the relaxation dispersion achieved with off-resonance spin lock T(?ρ) experiments. As compared with the off-resonance spin lock T(?ρ) method, a slower rotating frame relaxation rate was observed with RAFF, which under certain experimental conditions is desirable.     

Dielectric absorption in mixtures of anisole with some primary alcohols at microwave frequency

Dielectric properties of binary mixtures of anisole with methanol (MeOH), 1-propanol (1-PrOH), 1-butanol (1-BuOH) and 1-heptanol (1-HeOH) over an entire concentration range have been studied at a fixed temperature 40°C. The dielectric constant (ε′) and dielectric loss (ε″) of the binary mixtures of polar liquids have been determined at a microwave frequency of 9.1?GHz. The static dielectric permittivity (ε ₀) of the liquid samples was also determined using a precision LCR meter. Determined values of static dielectric permittivity (ε ₀) and dielectric permittivity (ε*) at 9.1?GHz frequency were used to evaluate relaxation time (τ) and high frequency limit dielectric permittivity (ε _∞). Dielectric parameters were interpreted in terms of molecular interaction between the anisole and alcohol molecules.     

Infrared intensity analysis of some MXY2 type molecules

Infrared intensity analysis of MXY₂ type molecules has been attempted. The dipole momentμ of C=O is obtained to be different for different moleculesviz. for CH₂O, 1.9052; for COCl₂, 1.1517; for COF₂, 0.6340; and for COBr₂, 0.7687. Similarly in the case of CSF₂ and CSCl₂ μ _C=S it was found to be 0.2473 and 0.2983 respectively. This shows that the effect of the electro-negative halogen atoms is very important. Presented at the ‘National Symposium on Molecular Spectroscopy’, Annamalai University, Annamalainagar on 28 February 1976.     

Relaxation times and NMR signals

The strength of signals in magnetic resonance imaging (and the resulting image contrast) depends not just on the number density of the nuclei being detected, but also on the relaxation times, T1 and T2. The relationship of signal strength to relaxation time depends on the particular choice of pulse sequences used to produce the signals. The effects of the T1 relaxation time on signal strength are discussed for the commonly used imaging techniques "partial saturation" and "inversion recovery." Production of spin echos and the effect of the T2 relaxation time on spin-echo signal strength are also discussed.     

Identification and intensity analysis on forbidden magnetic dipole emission lines of highly charged Al, Ar, Ti and Fe ions in LHD

Forbidden lines arising from magnetic dipole (M1) transitions in ground and 2s2p excited configurations of highly charged Al, Ar, Ti and Fe ions have been observed in the large helical device (LHD). Argon was puffed using a piezo-electronic valve and other metallic materials were injected using an impurity pellet injector into LHD plasma for the observation. The M1 transitions in vacuum ultraviolet (VUV) and visible regions are identified by analyzing their Doppler broadening, temporal intensity behavior and spatial intensity distribution. Wavelengths of these M1 transitions are determined with high accuracy and compared with previous experimental and calculated values. The line intensity ratios of the M1 transition to the allowed (E1) transition such as (ArX 5533 Å/165 Å, TiXIV 2118 Å/122 Å and FeXVIII 975 Å/94 Å) and 2s2p - (ArXV 5944 Å/221 Å) are measured as a function of electron density. Results on the ArX and ArXV are compared with a simple level-population calculation. As a result, the density dependence of the ratio is well explained mainly by a competition between two decay processes of the collisional de-excitation and the radiative decay due to the forbidden line emission, although a clear discrepancy between the experimental and calculated absolute values appears for the ArX ratio. Contribution of fast proton impact excitation, which is brought by 180 keV neutral beam injection (NBI) for plasma heating, is also analyzed with the calculation for the F-like ions of ArX, TiXIV and FeXVIII.     

Inhomogeneous Relaxation in Vibrated Granular Media: Consolidation Waves

We investigate the spatial dependence of the density of vibrated granular beds, using simulations based on a hybrid Monte Carlo algorithm. We find that the initial consolidation is typically inhomogeneous, both in the presence of a constant shaking intensity and when the granular bed is subjected to "annealed shaking". We also present a theoretical model which explains such inhomogeneous relaxation in terms of a "consolidation wave", in good qualitative agreement with our simulations. Our results are also in qualitative agreement with recent experiments.     

Investigation of MWS Relaxation in Nylon 1010 using Dielectric Relaxation Spectroscopy

Maxwell–Wagner–Sillars (MWS) relaxation in nylon 1010, arising from charge carriers accumulated at the interphase between amorphous and crystalline regions, has been investigated by means of dielectric relaxation spectra. In the frequency spectra of nylon 1010, dielectric permittivity showed high values at low frequencies originating from charge carrier movement. For the MWS relaxation, the dielectric strength was independent of temperature. The results revealed that there is a transition temperature, located between 110 and 120°C, resulting in the separation of two different charge carrier movement mechanisms. Below and above this transition temperature, the temperature dependence of the MWS relaxation time follows the Vogel–Tammann–Fulcher type, showing that the charge carrier transport is governed by the motion of the polymer chains. The change of charge carrier movement mechanisms is due to the onset of polymer chain motion in the interphase.     

Relaxation properties of weakly coupled classical systems

The relaxation properties of a small classical system weakly coupled to a large classical system which acts as a heat bath are described using a generalized Fokker-Planck equation. The Fokker-Planck equation is derived in general using a modification of the elimination of fast variables techniques previously described. The specific example in which the small system is a harmonic oscillator linearly coupled to the heat bath is treated in detail and it is demonstrated that there is a dynamic frequency shift as well as a statistical shift of the oscillator frequency.     

First-order properties and Buckingham birefringence of N2O and OCS – A computational (re)investigation

Prompted by recent experimental reinvestigations of the Buckingham birefringence of CO, CO₂, OCS and N₂O, we have carried out our own reinvestigation of the relevant first- and second-order properties entering the electric-field-gradient-induced birefringence effect of N₂O and OCS by means of state-of-the-art quantum chemical methods. The computed and experimentally derived results remain at significant variance, also in consequence of a remarkable disagreement between the ab initio and the experimental values of the quadrupole moment relative to the centre of the nuclear masses.     

Relaxation enhancement using liposomes carrying paramagnetic species

Studies were performed to investigate the effects upon the relaxation times of mouse organs of intravenously administered Mn-DTPA entrapped in multilamellar liposomes, Mn-DTPA, 0.9% NaCl entrapped in liposomes, 0.9% NaCl. Manganese concentrations in injectates and tissues were assessed with 54Mn and atomic absorption. T1 and T2 of freshly excised tissues were measured in an NMR spectrometer at 20 MHz and 37% C with IR and CPMG sequences. Entrapment of Mn-DTPA in liposomes increased 54Mn accumulation in liver by 207% and in spleen 1208% and reduced 54Mn in heart by 20% and in kidney by 24% relative to free Mn-DTPA. Statistically significant increases in relaxation rates were produced. However, the increase in relaxation rate per unit concentration of Mn in tissue is reduced by 31% in liver and 62% in spleen when Mn is delivered inside liposomes. These observations have implications for the design of NMR contrast agents.     

Relaxation of a dislocation in a nanocrystallite

Experimental studies of dislocations in nanoparticles are just beginning. The corresponding theoretical models are still lacking. In this context, the author analyzes relaxation of a dislocation in a nanoparticle. Mechanistically, this process is considered to occur primarily via dislocation drift induced by the stress-related image forces. Elementary dislocation displacements include the formation of a kink at one of the sides of the dislocation line, its diffusion along this line, and annihilation at the opposite side. For this mechanism, the dependence of the time of dislocation disappearance on the nanoparticle size has been identified.     

Relaxation, crystallization, and glass transition in supercooled liquid Ni

In this Letter, molecular dynamics (MD) simulations based on EAM many-body potential have been performed to investigate the differences of dynamical heterogeneity in the course of crystallization and glass transition, respectively. The crystallization of liquid, detected at a cooling rate of , is characterized by the appearances of the second plateau in mean square displacement (MSD) and the nonzero plateau in non-Gaussian parameter (NGP). It implies that the non-diffusive rearrangement of atoms occurring at a certain temperature and relaxation time leads to nucleus forming. The glass phase forms as the cooling rate increases to . There is no second plateau in MSD appearing in the formation of metallic glass, indicating the diffusive motion of atoms. The non-Gaussian characteristic in NGP is more obvious at low temperatures.