Proton spin-lattice relaxation in liquid water and liquid ammonia

The proton spin-lattice relaxation time has been measured at 20·8 Mc/s for a series of solutions of water in heavy water and solutions of ammonia in heavy ammonia for the temperature range from the melting point to the liquid-vapour critical temperature. Measurements have also been made for water over limited temperature ranges at several fixed densities.

The contributions to the spin-lattice relaxation time from direct dipolar and spin-rotation interactions have been separated. The spin-rotation interaction contribution appears to be the same for H₂O as for HDO and also as between NH₃, NH₂D and NHD₂ and this result is justified. The correlation times for molecular re-orientation, τ_d, and for molecular angular velocity, τ_sr, are derived from the results and in so doing some support for the Hubbard [12] relation betweent τ_sr and τ_d is adduced. It is found that at the critical temperature τ_sr?τ_d which contrasts with other liquids for which it is usually found that τ_sr??τ_d. The spin-rotation interaction constants in the water and ammonia molecules are found to be approximately 120 kc/s and 80 kc/s, respectively.

An attempt to separate the inter- and intra-molecular contributions to the dipolar spin-lattice relaxation time is possible in principle, in spite of the rapid proton exchange, but is frustrated by the fact that the equilibrium constants are little different from their statistical values. Nevertheless there is evidence that the two interactions vary in much the same way with temperature.

The correlation times deduced from the dipolar relaxation time show close relationship with dielectric, self diffusion and deuteron relaxation time data.

It is suggested that the re-orientation of both water and ammonia molecules may be by a small angle Brownian diffusion even near the critical temperature.     

Proton spin-lattice relaxation in MBDBP

We have measured the proton spin-lattice relaxation rate R in 4,4′-methylenebis(2,6-di-t-butylphenol) (MBDBP) and MBDBP-OD (deuteriated hydroxyl proton) between 88 K and 380 K. The experimental results are compared with those from a previous study in the closely related but simpler molecule 4-methyl-2,6-di-t-butylphenol (MDBP). The present experiment is analysed in terms of relaxation resulting from intramolecular reorientation modulation of the proton spin-spin interaction. This intramolecular reorientation involves different combinations of superpositions of methyl, t-butyl, aromatic ring and hydroxyl group reorientation and a discussion is presented concerning the effects on the relaxation of superimposing these motions. The MBDBP-OD data is best fitted with the assumption that only methyl and aromatic ring reorientations occur. In MBDBP it is found that, in addition, an OH flip-flop motion is superimposed on the aromatic ring reorientation.     

Proton spin-lattice relaxation in iron fluosilicate

Proton T₁ of FeSiF₆·6H₂O is proportional to exp (Δ/kT)at liquid helium temperatures, with Δ ≈ D - 3E. We find the crystal field splitting of the Fe²⁺ ion in this salt to be D = (12.2 ± 1.0) cm^-1 using E = 0.54 cm^-1.     

Proton spin-lattice relaxation times in ytterbium hydrides

The measurements of the proton (NMR) spinlattice relaxation times have been made in a series of ytterbium hydrides, YbH _x . Results are reported forx=1.80, 1.95, 2.00 and 2.62 and temperatures 4.2T297K. In the orthorhombic phase (1.80x2.00), the spin-lattice relaxation times are dominated by the hyperfine interaction of protons with conduction electrons and the spin diffusion mechanism. In the cubic phase (x=2.62), the relaxation times are five orders of magnitude shorter than in the orthorhombic one. This is interpreted in terms of the proton coupling with the Yb³⁺ ion spin fluctuations.     

Proton dipolar spin-lattice relaxation in hexagonal ice

The ultraslow motion of defects in high purity hexagonal H₂O ice has been studied by proton dipolarT _1D measurements in the strong collision limit, using the Jeener technique. The obtained NMR correlation times agree rather well with both the Schottky H₂O diffusion timest _s=r ²/6D and the deuteron correlation times in D₂O ice, suggesting that Schottky rather than interstitial diffusion dominates spin-lattice relaxation in both H₂O and D₂O ice.On leave of absence from University of Ljubljana, Institute J. Stefan.     

Proton spin-lattice relaxation in aqueous ionic solutions

The proton spin-lattice relaxation time, T ₁, has been measured for aqueous solutions of sodium, potassium, rubidium and magnesium chlorides up to a concentration of about 4N at 25°c. The sodium and the magnesium chloride solutions were also measured at 60°c and 100°c. The variation of 1/T ₁ is not linear with concentration, at least above about ¼N, in contrast with previous reports [1, 2]. The behaviour depends markedly on the nature of the salt and on the temperature. It is shown that almost the whole of the variation of T ₁ as compared with that of water can be directly and simply related to the corresponding changes in the shear viscosity of the solutions. It is noted that the viscosity correction is better the higher the temperature of the solution.     

Proton spin-lattice relaxation time of hydrated gelatin

In this work we obtain a model to describe the relaxativity of water molecules, adsorbed on macromolecules, as a function of the concentration. Excellent agreement with experimental data was obtained. The model allows us to estimate the adsorption energy of water molecules on different sites of the macromolecules.     

Proton spin-lattice relaxation and charge transfer in quinolinium-tetracyanoquinodimethane

The proton spin-lattice relaxation of selectively deuterated quinolinium-tetracyanoquinodimethan O(D₈) (TCNQ)₂ is reported. Its temperature dependence indicates a metallic state down to at least ～ 130°K. The magnitude of the relaxation rate, when compared to the rate of the non-deuterated compound indicates nearly complete charge transfer.     

Proton spin-lattice relaxation in deuterated diluted copper tutton salts

The spin-lattice relaxation time, T_1I, of the protons in (Cu,Zn)Cs₂(SO₄)₂·6(H,D)₂O was measured. The sample was 94% deuterated and contained 0.5% Cu²⁺ ions. The T_1I measurements were carried out at liquid helium temperatures and at fields in the region from 5–15 kOe. Under these conditions, T_1I shows a strong dependence on the direction of H₀ with respect to the crystal axes, in the magnetic K₁–K₃ plane. This angular dependence has been accurately determined close to the K₁ and K₃ axes, at 1.4K. Between the angular dependent behaviour of the proton relaxation time and the EPR spectrum of the Cu²⁺ ions exists a striking correlation: T_1I exhibits sharp minima at angles where the frequency distance between the EPR lines is about equal to the proton resonance frequency.The observed temperature dependence in the liquid helium region is weak and can very well be described with a factor (1−P²₀)⁻¹, where P₀ denotes the electron polarization. The field dependence of T_1I appears to be between H^1.0₀ and H^1.5₀.     

Nuclear spin-lattice relaxation in the mixed state of superconducting niobium

Pulsed NMR measurements of the spin-lattice relaxation timeT ₁ have been carried out in niobium metal, in order to investigate the elementary excitation spectrum in the superconducting mixed state. The dependences ofT ₁ on temperature, external field, and mean free path were determined. The results below ～5°K were in agreement with the theory of field-induced gapless superconductivity. The best fit was obtained with a scale factor 0.35±0.2, in agreement with recent ultrasonic attenuation results. Anomalously fast relaxation was observed above ～5°K, which could not be interpreted in terms of the present theory of thermal vortex fluctuations.     

Proton spin-lattice relaxation time in the α-VHx

The ¹H spin-lattice relaxation time T₁ has been measured in the α-VH_x. It is found that T₁ in the α-phase is essential ly determined by contact hyperfine interactions, and its variation with hydrogen concentration is in accord with a rigid-band model.     

Proton spin-lattice relaxation by critical polarization fluctuations in KH2PO4

The observed anomalous decrease in the proton spin-lattice relaxation timeT ₁ on approaching the Curie point in a rather pure KH₂PO₄ single crystal is explained by magnetic dipolar coupling to the ferroelectric mode. The isolated “non-interacting” O?H...O proton flipping time is estimated from theT ₁ data as τ=0.66·10^?12 sec for the paraelectric phase and τ=2.24·10^?12 sec for the ferroelectric phase, in good agreement with the results obtained from other methods.     

Proton spin-lattice relaxation time in ordering VHx alloys

Proton spin-lattice relaxation time is determined in VH_0.68 and VH_0.73 alloys in the temperature range of β₁, β₂ and δ ordered phases (400-100 K). Experimental results are described in terms of dipole-dipole interaction mechanism. On comparing calculated and experimental data in the complete temperature range the values of temperature dependent activation energy E_a and time constant τ₀ are estimated.     

Intramolecular and intermolecular contributions to the spin-lattice relaxation of protons in benzene and cyclohexane

Temperature dependences are found for the intramolecular and intermolecular contributions to the spin-lattice relaxation of protons in benzene and cyclohexane by dilution in deuterated analogs. The intermolecular contribution in benzene is discussed on the basis of the model for the molecular distribution found from x-ray diffraction studies. The Hubbard correction to the intermolecular contribution is calculated on the basis of the experimental parameters corresponding to rotation and translation. The results imply discontinuous translational motion of molecules in both liquids.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii Fizika, No. 3, pp. 116–121, March, 1971.In conclusion the author thanks T. N. Khazanovich for useful advice.     

Ultrasonic absorption in binary liquid mixtures

Ultrasonic absorption in binary liquid mixtures containing benzene, chloroform, cyclohexane and toluene with triethylamine, a rotational isomeric relaxing liquid, as a common component has been studied at a frequency of 7.56 MHz. A pulse techrique has been used for the measurement of absorption with an accuracy of ±5%. Bauer-Sette formula has been used to calculate the absorption of these liquid mixtures at different concentrations. The theoretical values evaluated on the basis of Bauer-Sette theory appear to have good agreement with experimental values. In view of the discrepancy pointed out by Mallikarjuna Rao and Suryanarayana, the mixtures of benzene and ethylacetate have been studied in this context and found the theoretical values coinciding with experimental values.     

Nonexponential nuclear spin-lattice relaxation in the isotropic phase of thermotropic liquid crystals

In the isotropic phase of nematic and smectic liquid crystals T₁ of CH3 and chain protons is larger than that of ring and ring-neighboured protons being caused by fast CH₃ reorientation and internal motions in chains, respectively.