Hermann Gerhard Hertz

Nuclear magnetic relaxation in the presence of intramolecular rotations

Abstract The proton magnetic relaxation rate 1/T 1 for labelled methanols CH 3 OD and CD 3 OH in mixtures with (CD 3 ) 2 SO has been measured as a function of temperature and frequency. In the low-temperature region, maxima and a strong frequency dependence of 1 T 1 were found. The results were evaluated on the basis of intra- and intramolecular relaxation theories. The intermolecular relaxation rate, to which this study is mainly devoted, is found to be markedly smaller than predicted by the theory. Some information about the motion of molecular groups in methanol is obtained.

Longitudinal proton relaxation rates in aqueous Ni2+ solutions as a function of the temperature, frequency, and pH Value

Abstract Proton relaxation times T 1 in 0.1 molal aqueous Ni(ClO 4 ) 2 solutions to which various amounts of HC1O 4 are added have been measured. The temperature range covered was 1–80°C; the proton resonance frequencies used were 2, 6, 12, 25, 48, 60, and 88 MHz. At pH = 3 and temperatures lower than ≈ 35°C the observed relaxation rate is partly determined by the proton exchange process from the first hydration sphere to the bulk, whereas at pH = 0.1 the proton exchange is so fast that it is difficult to detect. The frequency dependence of the relaxation rate in the first hydration sphere changes in a remarkable way as one goes from high to low temperatures. Numerical values for the residence time of the proton in the first hydration sphere are given. In the appendix proton relaxation rates of the system (CH 3 ) 4 NCl + NiCl 2 + D 2 O are given as a rough example for the translational contribution to the relaxation rate.

Rotational, internal rotational, and translational motion of acetic acid and dimethyl sulfoxide in their liquid mixture (with some results for DMSO dissolved in MEOH)

The proton magnetic relaxation rate of DMSO in the mixture 33.3 mole % DMSO + 66.7 mole % CD3COOD has been measured in the temperature range 3.5 < 1000/T < 6.0 K and at six frequencies 6 < ν < 144 MHz. The intramolecular relaxation rate was determined by the aid of the isotopic substitution technique. The rotational correlation time of “the molecule” and the time constant of the internal motion have been extracted from these experimental results. The corresponding measurements were also performed on DMSO in the solvent CD3OD (71 mole %) where no internal motion effect appeared in the temperature dependence of the relaxation rate. Furthermore, proton relaxation rates of the acetic acid methyl group and deuteron relaxation rates of the acid methyl and OD group are reported. Again, the data are given in the temperature range as above and for a number of frequencies. Rotational time correlation functions g(t) for the axid molecule are derived. Finally we present experimental results for the self-diffusion coefficients of both mixture partners DMSO and AcH and of DMSO in the solvent MeOH.

Nuclear magnetic relaxation of atomic neon-21 in liquid solution

The investigation of magnetic relaxation of noble gas nuclei in liquid solutions is a relatively new and promising field of interest in NMR. The reason for this interest lies in the fact that noble gas nuclei may serve as very informative probes for their surroundings, since they are uncharged and inert. So far, these relaxation studies have been restricted to xenon and krypton. In the present work we report first relaxation measurements on 2’Ne. The natural noble gas xenon contains two isotopes, 13’Xe (I =

Square-root concentration dependence of nuclear magnetic relaxation rates in strong electrolyte solutions

) and 129Xe (I = f ). It has experimentally been shown that 13’Xe relaxes by the electric-field-gradient- quadrupole interaction (QF interaction) (1, 2). This quadrupole relaxation of 13’Xe has also been investigated in detail by MD computer simulation techniques (3). Ex- perimental relaxation time measurements on both i3’Xe and ‘29Xe have been per- formed in more than 60 different solutions and also in many aqueous solutions of dia- and paramagnetic salts, aqueous mixtures of organic solvents, and solutions of crown ethers (4). The relaxation behavior of both xenon nuclides has also been com- pared in isotropic and anisotropic liquids (5). Two independent studies (4,5) revealed that 129Xe is relaxed by the spin-rotation interaction. in 1987 one of the present authors reported the first 83Kr (I = 4 ) relaxation data in liquid solutions and it could be shown that the 83Kr relaxation behavior is of quadrupolar nature and is thus similar to 13’Xe relaxation (6). From a comparison of 83Kr and 13’Xe chemical-shift values it could be concluded that the diamagnetic shielding of the noble gas atoms is dom- inating the chemical shift of the nuclei (6). This result has also been obtained by Diehl and co-workers ( 7) by comparison of 2’Ne and i31Xe shifts in solutions. In the following we will present our results of the first T, measurements on 2’Ne of atomic neon dissolved in several liquids and we will give a comparison of these results with the corresponding 13’Xe data. For the measurements we used neon gas in which the isotope 2’Ne was enriched to 96.7% (IC Chemikalien, Munich, Germany). The different liquids which we used as solvents for the neon gas were of c.p. grade and have been freed from oxygen. The samples used for the measurements were saturated solutions under a gas pressure of 30-40 bar. The concentration of neon gas in the different liquids varied from 0.01 to 0.05 mol/liter depending on the respective solubility. The solutions under pressure were kept in thick-walled Duran glass tubes. The outer diameter of the tubes was 0.9

Galvanic cells containing only one type of anion (or correspondingly, one type of cation)

Abstract 23 Na nuclear magnetic relaxation rates in aqueous solutions of NaClO 4 , NaI, and NaBr and of NaBr dissolved in HMPT have been measured as a function of the salt concentration down to concentrations c ⪅ 10 −2 m. In the same way the relaxation rates of 7 LiBr and 87 RbX, X = Cl, Br, I, in aqueous solution have been studied with the effort to reach solute concentrations as small as possible. All the ionic nuclei in question here relax by electric quadrupole interaction and it has been shown that the relaxation rates are proportional to √ c at small concentrations.

A comparison of our electrolyte diffusion treatment with the conventional one

We now turn to the class of simpler galvanic cells which are built up of only three constituents. Thus we may have two different cationic constituents and only one anionic constituent. As a first example, we choose the NaCl + KCl system. The galvanic cell with an electrolyte containing two different anionic species and only one cationic constituent should be treated in an analogous way.

The galvanic cell with a redox electrode

We have now to compare our treatment of the mass flux, the electric current, and the excess mass and energy fluxes in inhomogeneous systems with the theory generally accepted and found in the literature1,2,3). We wish to give as simple an analysis as possible and therefore we consider a binary electrolyte-water system, for instance NaCl + H2O. Of course the NaCl concentration is not uniform throughout the system. In the conventional treatments the fluxes are the centre of interest, and thus we shall mainly discuss the interconnection between electric current density and mass flux on the one hand and the field properties determining the system on the other hand. Usually the mass fluxes are referred to the solvent fixed coordinate system and instead of the gradient of the solute particle density the gradient (or gradients) of the chemical potential are written in the equations. We assume that the electrodes in the conventional sense — if at all present — are remote and processes at the electrodes do not enter explicitly into the treatment. Comparison of the circumstances at the boundary metal/electrolyte will be postponed to the next chapter.

The moving boundary method

We consider a system as depicted in Fig.33. nOpen image in new window n nFig. 33 nSchematic representation of a galvanic cell involving a redox electrode.

The galvanic cell with an oxygen electrode

The equations of the preceding section — no explicit considerations of the electrodes — have their most important application in conjunction with the moving boundary method which serves to measure transport numbers1). In a typical experiment we have two different cations and only one anion. In order to remain within the general framework of the main treatment we consider the special constituents Na, Li, and Cl. The replacement of K by Li is necessary for technical reasons as will be seen later. Now the set of eqs.(112)–(114) only contains two equations: the third one, eq. (114) is no longer necessary. Thus we have n n