Nuclear Magnetic Resonance and Relaxation in Solid Hydrogen

[No abstract included

Anisotropy of the \u3csup\u3e19\u3c/sup\u3eF Chemical Shift of Trapped CHF\u3csub\u3e3\u3c/sub\u3e and NF\u3csub\u3e3\u3c/sub\u3e

We have studied the 19F chemical‐shift anisotropy in NF3 and CHF3 trapped in β‐quinol clathrates. It is known that molecules trapped in these compounds become aligned at low temperatures so that studies of relatively isolated oriented molecules become possible. The nuclear magnetic resonance was observed at several frequencies with the magnetic field applied at various angles relative to the crystal axis. The orientation of the molecules in the cavity and the dipolar broadening due to the lattice protons could be estimated rather closely by a qualitative analysis of the line shapes. The principal components of the chemical‐shift tensor of NF3 could be determined from the observed variation of the first and second moments of the line with the strength and orientation of the magnetic field. This determination was further substantiated by the good agreement between the calculated and observed line shapes for various values of the magnetic field. For CHF3, where the chemical‐shift anisotropy is smaller, only a cruder analysis was practicable. The values of the anisotropy of the chemical‐shift tensor obtained were σ∥−σ⊥ = (390±60) ppm for NF3 and σ∥−σ⊥ = (105±20) ppm for CHF3, where σ⊥ is the average of the two components of the chemical‐shift tensor perpendicular to the fluorine bond direction. For NF3 a difference of (140±40) ppm between the two perpendicular components was found, indicating a deviation from uniaxial symmetry of the NF bond. The sign and order of magnitude of the chemical‐shift anisotropy are discussed and can be understood on the basis of current ideas about the relationship between the bond characters and the chemical‐shift anisotropy

Sublattice Magnetization in Several Rare‐Earth and Yttrium Iron Garnets by Means of \u3csup\u3e57\u3c/sup\u3eFe NMR

We have observed the NMR of 57Fe on the a and d sublattices of YIG, GdIG, and LuIG between 4° and 200°K. Using the spin‐echo technique the frequencies could be determined to within a few kHz. For LuIG the determination of the frequency was less accurate due to the presence of the lutetium resonances which overlay the iron resonances. Assuming the frequency is proportional to the sublattice magnetization, the data were fitted to the equation derived from spin‐wave theory. For YIG and LuIG inclusion of the T 7/2 term was necessary to represent the data above 40°K. Using the theory of noninteracting spin waves we have derived expressions for the sublattice magnetizations in terms of the exchange integrals Jaa, Jad, Jdd , and J′ad , where J′ad describes interactions between next‐nearest‐neighboring pairs of spins on the a and d sublattices. Our experimental results indicate that Jaa and Jdd are not negligible. The T3/2 coefficients were found to be about 15% larger for LuIG than for YIG. Our value of the exchange stiffness constant of YIG is 10% larger than those determined calorimetrically and hence agrees with values determined by microwave instability measurements. For LuIG our value of this constant agrees with the specific heat value

A high-resolution study of the OH-stretch fundamental of methanol

The OH-stretch fundamental of CH3OH has been observed with 0.025 cm-1 resolution between 3430 and 3940 cm-1 and the resulting spectrum deconvoluted using the procedure of P. A. Jansson. Approximately 600 lines have been assigned to a total of 67 P- or R-branch series and some 30 excited state levels have been determined. Of these, 14 belong to the lowest torsional state with n = 0, 13 to N = 1 and 3 to N = 2. A nonlinear least-squares fit to these levels varying the major parameters used by Y. Y. Kwan and D. M. Dennison in their analysis of the normal state produces an rms deviation between observed and calculated levels of 0.51 cm-1. Variation of all the parameters including those of the smaller Kirtman perturbation terms produces only a slight improvement in the fit. Both analyses yield a barrier height of 411 cm-1 in the excited vibrational state as compared to the normal state value of 373 cm-1. A number of unexplained anomalies appear in the spectra including large and irregular changes in the coefficient of J2 + J for different torsion-rotation states.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/22170/1/0000601.pd

Computational approaches to understanding reaction outcomes of organic processes in ionic liquids

This review considers how various computational methods have been applied to explain the changes in reaction outcome on moving from a molecular to an ionic liquid solvent. Initially, different conceptual approaches to modelling ionic liquids are discussed, followed by a consideration of the limitations and constraints of these approaches. A series of case studies demonstrating the utility of computational approaches to explain processes in ionic liquids are considered; some of these address the solubility of species in ionic liquids while others examine classes of reaction where the outcome in ionic liquids can be explained through the application of computational approaches. Overall, the utility of computational methods to explain, and potentially predict, the effect of ionic liquids on reaction outcome is demonstrated

Molecular dynamics simulation studies of the interactions between ionic liquids and amino acids in aqueous solution

Although the understanding of the influence of ionic liquids (ILs) on the solubility behavior of biomolecules in aqueous solutions is relevant for the design and optimization of novel biotechnological processes, the underlying molecular-level mechanisms are not yet consensual or clearly elucidated. In order to contribute to the understanding of the molecular interactions established between amino acids and ILs in aqueous media, classical molecular dynamics (MD) simulations were performed for aqueous solutions of five amino acids with different structural characteristics (glycine, alanine, valine, isoleucine, and glutamic acid) in the presence of 1-butyl-3-methylimidazolium bis(trifluoromethyl)sulfonyl imide. The results from MD simulations enable to relate the properties of the amino acids, namely their hydrophobicity, to the type and strength of their interactions with ILs in aqueous solutions and provide an explanation for the direction and magnitude of the solubility phenomena observed in [IL + amino acid + water] systems by a mechanism governed by a balance between competitive interactions of the IL cation, IL anion, and water with the amino acids

Opera and Hypnosis: Victor Maurel’s Experiments with Verdi’s Otello

One day in his private home on the avenue Bugeaud, in Paris’s sixteenth arrondissement, the famous baritone Victor Maurel hosted a meeting which combined music with hypnotism of a young woman