NMR studies of single crystals of H2: II. The spectrum of isolated ortho-H2 pairs

Schweizer, R.; Washburn, S.; Meyer, Horst; Harris, A. B.

doi:10.1007/bf00119192

Cited by 15 publications

(11 citation statements)

References 15 publications

(5 reference statements)

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“…Because this effect might well be dependent on strains in the sample, more experiments on crystals with a different preparation should be carried out. 2. The concentration dependence of ~" between 0.2% and 1% o-H2 was found to be small over the whole temperature range.…”

Section: Discussionmentioning

confidence: 89%

“…A discussion of the transition rates between the rotational states for single O-HE was presented in Ref. 1. There it was shown that from the observed temperature dependence of the single o-H2 spectrum down to 0.05 K, the transition rate f~ between the Jz levels is "fast," i.e., ~ >> d, where d = 57 kHz is the nuclear dipolar interaction constant.…”

Section: Alternative Explanations Of the Resultsmentioning

confidence: 99%

“…The net effect is the same, allowing ortho impurities to "diffuse" through the lattice and finally form clusters. Calculations show that the presence of o-H2 neighbors slows down the jumping rate u through the EQQ interaction and that the temperature dependence of this rate is small, at least above about 0.5 K. A high-temperature expansion leads to the expression 12 u = 0.41 x IO-sX-1/2(1 +0.05/T+ 9 9 ") Hz (2) where the value 0.05 is only an estimate and the result of a number of approximations. Hence, the average time spent on a lattice site then becomes rl = (12v)-1~:30 min forX=l%, T=2K…”

Section: Orientational Energies and Quantum Diffusion A Short Reviewmentioning

confidence: 99%

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NMR studies on single crystals of H2. III. Dynamic effects

1980

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The time-dependent effects in the NMR spectrum of ortho-Hz impurities in two single crystals of Hz are investigated over the temperature range between 0.02 and 3 K and for an ortho-Hz mole fraction X between 0.1% and 2%. The disappearance of the signal from isolated o-H2 impurities, after cooling the crystals to a given temperature, and the simultaneous increase of the signal from isolated o-H2 pairs indicates a clustering process. The characteristic times from both spectra are comparable and pass over a flat maximum near T = 0.3 K. The clustering process then accelerates drastically as T is decreased below 0.1 K. The characteristic times are only weakly dependent on the concentration X. Furthermore, the subsequent decay of the o-H2 pair signals with time suggests a slow diffusion of pairs and formation of larger clusters. It is found that the period associated with the decay of in-plane pairs (having their axis parallel to the basal plane) is considerably shorter than that for the out-of-plane pairs. The resui'ts are discussed in the light of the theory of hopping impurities (resonant ortho-para conversion) and possible coherent tunneling effects at low temperamres. Finally we briefly report some studies of the longitudinal relaxation time for the o-H2 pair NMR lines.

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Section: Discussionmentioning

confidence: 89%

Section: Alternative Explanations Of the Resultsmentioning

confidence: 99%

Section: Orientational Energies and Quantum Diffusion A Short Reviewmentioning

confidence: 99%

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NMR studies on single crystals of H2. III. Dynamic effects

1980

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“…The ortho-para hydrogen mixtures can be regarded as a model quadrupolar system where the interactions are known and are of simple electrostatic nature-the number of ingredients to produce a glasslike state is minimal, just one chemical specimen. The zero-point motion effects on orientational ordering have been demonstrated in the NMR spectrum on a coupled pair of ortho-H 2 molecules 29 and in ortho-para H 2 mixtures. 30 The NMR experiments with rapid variations of the line shapes with temperature for solid ortho-para hydrogen systems may substantiate the discontinuous transition picture from the orientationally disordered to the QG phase, though with some caution in view of the ambiguity in the interpretation of NMR data.…”

Section: Discussionmentioning

confidence: 97%

Quantum orientational glasses: Large-Mlimit approach

Kopeć

1996

Phys. Rev. B

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We study a generalization of the quantum model of fully isotropic uniaxial p-polar glasses with multicomponent orientational degrees of freedom and Gaussian-distributed random, infinite-range exchange interactions. The quantum effects are associated with a finite moment of inertia ͑treated quantum mechanically͒ of a particle with M orientational degrees of freedom. The system exhibits a quantum phase transition separating the glassy and paraorientational phases regulated by a parameter ⌬ ͑inverse of the moment of inertia of a particle͒. The model allows in the limit M →ϱ for an exact solution both in the glassy and disordered phases for an arbitrary value of the parameter p. We have analytically established the closed form of the self-consistency solution for the dynamic order parameter within the replica method and show that different spin glass transition scenarios emerge as a function of the parameter p. Whereas for pϭ1 ͑dipolar case͒ the solution of the quantum glass model is exact within replica symmetry, with a continuous phase transition along the critical line T c (⌬) we showed that the model for pу2 ͑multipolar case͒ undergoes a first-order phase transition. In the latter case within the Parisi replica-symmetry-breaking scheme we have determined a functional Parisi-like order parameter q(x) and demonstrated that for pу2 a single step of the replica symmetry breaking is the exact solution within the glassy phase. For the physically most relevant case of pϭ2 ͑quantum quadrupolar glass͒ the ⌬-T phase diagram has been computed numerically.

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“…(6), (11) and (12). The calculated anisotropic shifts are compared with the experimental data in Fig.…”

Section: Comparison With Experimental Datamentioning

confidence: 99%

Interpretation of 1H NMR results of HD impurities in solid H2. II. Anisotropic resonance frequency shifts

1992

J Low Temp Phys

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The anisotropic resonance frequency shift ~v= v(HD) -v(ortho-He singles) of the I H resonance spectrum observed in low ortho-concentration (X <_ 0.01) solid He single crystal samples is examined The observed sign and magnitude of the resonance frequency shift as well as its anisotropy are explained by the spin-rotation interaction and the second order effects of the intra-molecular dipole-dipole interaction of ortho-H2 singles. The calculations, without adjustable parameters, are in reasonable agreement with the experiments. This conclusion is at variance with the suggestion by Delrieu and Sullivan.

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NMR studies of single crystals of H2: II. The spectrum of isolated ortho-H2 pairs

Cited by 15 publications

References 15 publications

NMR studies on single crystals of H2. III. Dynamic effects

NMR studies on single crystals of H2. III. Dynamic effects

Quantum orientational glasses: Large-Mlimit approach

Interpretation of 1H NMR results of HD impurities in solid H2. II. Anisotropic resonance frequency shifts

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