Spin Rotation Effect Research Articles

The elastic constants of dysprosium and holmium

The five single-crystal elastic constants of dysprosium and holmium have been measured within the temperature range 4.2 to 300 K. The large contributions to the elastic constants due to domain and spin rotation effects were eliminated by applying a magnetic field of 2.5 T along the magnetic easy directions. Extrapolation of the temperature dependence in the paramagnetic region to 0 K indicates large magnetic contributions to the elastic constants which have been interpreted as arising from the strain dependence of the exchange energy. Analysis of these contributions permits the evaluation of the first and second derivatives of the nearest and next-nearest exchange interaction parameters. The results are consistent with more limited information obtainable from the anomalous thermal expansion and are consistent with an oscillatory J ( r ).

Spin-rotation effects on radiationless transitions

The possible role of first and second order spin-rotation interactions in radiationless transition processes is discussed.

N.M.R. relaxation time studies in liquid methyl iodide

The spin-lattice relaxation times of the various nuclei in methyl iodide, methyl iodide-d 3, and carbon-13 methyl iodide (13C, 1H, 2D) were measured between 210 and 350 K. The separation of the proton-proton intermolecular relaxation was accomplished by a dilution study in methyl iodide-d 3; the resulting intermolecular contribution agreed well with the existing theories for this mechanism. It was found that the spin-rotation interaction contributed significantly to the intramolecular relaxation of both the protons and the carbon-13. For both nuclei the separation of the spin-rotation interaction from the intramolecular dipole-dipole interaction was accomplished without making any assumptions about the temperature dependence of the spin-rotation relaxation time. The resulting spin-rotation relaxation times for both carbon-13 and protons offer evidence that the large spin-rotation effects are due to the methyl group reorientation.

ESR Linewidths in Solution. V. Studies of Spin–Rotational Effects Not Described by Rotational Diffusion Theory

We have measured the ESR linewidths of ClO2 as a function of temperature in a number of solvents. The dominant spin relaxation mechanism is the motional modulation of the spin–rotational interaction; therefore, the measurements yield the autocorrelation times for angular momentum. The experimental data can be correlated with the aid of the relation τJα−1 = (8πr03ηκ / Iα) + Δα2[τJβτJγ / (τJβ + τJγ)], where τJα is the autocorrelation time for the component of angular momentum along the αth molecular axis (α = x, y,z), Iα is the moment of inertia about the αth axis, η is the coefficient of viscosity for the solvent, r0 is a translational hydrodynamic radius which is determined experimentally by means of diffusion experiments, Δα is the frequency of precession of the αth component of angular momentum, a frequency which vanishes for spherical tops and linear molecules and can be calculated entirely in terms of known components of the moment of inertia, and κ is an adjustable parameter which is assumed to be independent of temperature and viscosity but dependent upon solvent. There are three such equations for the three correlation times τJα, and they can be combined with linewidth formulas to yield the ESR linewidth as a function of T, η, and κ. The linewidth-versus-(T / η) curves can then be fitted by adjusting the value of the single parameter κ for each solvent. The parameter κ1/2 is a measure of the anisotropy of the intermolecular potentials; it approaches unity for very anisotropic interactions and zero for hard-sphere interactions. A derivation of the equation above is given along with an analysis of the relation between κ and the intermolecular potential. Various corrections to the results are presented together with a critique of the present theory and a comparison with other work.

Spin Exchange in Solutions of di-Tertiary-Butyl Nitroxide

The ESR linewidths of dilute solution of di-tertiary-butyl nitroxide (DTBN) in n-pentane and propane have been studied. Corrections have been made for (1) spin-rotational effects, (2) the variation of concentration with temperature, (3) the line-shape distortion of overlapping “strongly exchanging” lines, (4) the exchange narrowing of inhomogeneous linewidth contributions arising from proton extra hyperfine splitting, and (5) the temperature dependence of the diffusional step length λ. Existing theories of spin exchange appear adequate to explain the low-concentration data; at high concentration it is not possible to make all the corrections discussed above and the comparison of theory and experiment is not meaningful. In n-pentane we found that (zT/z).Jλ02 = 5×1012 Å2 sec−1 and JzT = 4.9×1011 sec−1, where J is minus two times the exchange integral, λ0 is the diffusional step length at the freezing point, zT is the mean total number of molecular nearest neighbors, and z is the number of new radical nearest neighbors encountered in each jump. The results for DTBN in propane are similar.

ESR Linewidths in Solution. III. Experimental Study of the Solvent Dependence of Anisotropic and Spin—Rotational Effects

The ESR linewidths of vanadyl acetylacetonate in diphenylmethane have been studied as a function of temperature. The results confirm the analysis made previously for the linewidths of vanadyl acetylacetonate in toluene. The major contributions arise from anisotropic g and hyperfine interactions and from spin—rotational effects. The parameter λ⅓=r/3.045 Å, where r, the hydrodynamic spherical radius of the radical, is introduced as an adjustable parameter. This one parameter is sufficient to enable the theory to explain the linewidth results in a number of solvents, but a slightly different value of λ is required for each solvent. This variation may be due to solvation effects. Studies of deuterated vanadyl acetylacetonate in carbon disulfide indicate that neither intermolecular dipolar interactions nor unresolved proton extrahyperfine splittings contribute appreciably to the linewidth.

ESR Linewidths in Solution. I. Experiments on Anisotropic and Spin—Rotational Effects

The linewidths of the hyperfine components of the ESR spectra of vanadyl acetylacetonate in liquid toluene have been measured as a function of concentration, temperature, and applied field. The g-tensor and hyperfine-tensor components have been determined and used, along with the spectral data, to determine the Debye rotational correlation time τR. This analysis agrees very well with the experimental observations. A residual linewidth, not dependent upon the above mechanism, and independent of nuclear quantum number and applied field, has been studied and found to vary as T/η, where η is the viscosity. This residual linewidth is ascribed to a spin—rotational interaction.

Molecular motion in liquid benzene by nuclear magnetic resonance

The proton spin-lattice relaxation time, T 1, has been measured for a series of mixtures of benzene in perdeuterobenzene for the liquid in equilibrium with its vapour over the temperature range from below the normal freezing point up to the critical temperature. The two contributions to T 1 due to interactions within the molecule (T 1 intra) and between molecules (T 1 inter) have been separated and are found to be very different in magnitude and in variation with temperature. The variation and magnitude of T 1 inter correlates well with other translational motion dependent properties such as self diffusion and viscosity. The correlation of T 1 intra with other re-orientation dependent properties such as deuteron T 1 and Rayleigh scattering is poor. The observed variation in T 1 intra and in particular the broad maximum at higher temperatures is then interpreted as due to a combination of dipolar and spin-rotation effects. This interpretation results in good agreement between the activation energies for re...