Jean Jeener

Investigation of exchange processes by two‐dimensional NMR spectroscopy

A new general technique for the investigation of exchange processes in molecular systems is proposed and demonstrated. Applications comprise the study of chemical exchange, of magnetization transfer by inter‐ and intramolecular relaxation in liquids, and of spin diffusion and cross‐relaxation processes in solids.

Unified derivation of the dipolar field and relaxation terms in the Bloch‐Redfield equations of liquid NMR

The standard theory of NMR relaxation in liquids (with molecular motion described as a classical Brownian motion, and including intermolecular spin–spin couplings) is re‐examined, taking great care not to drop significant contributions from the dipolar coupling between distant molecules. This results in ‘‘modified Bloch–Redfield equations’’ for the spins in a single molecule, valid at all spin temperatures, which contain both the usual relaxation terms and a coupling of each spin with a classical average dipolar field. Delicate issues raised in this derivation, like the neglect of quantum correlations between spins on different molecules at (repeated) initial times, are discussed with the help of exact calculations (for all spin temperatures) performed on a simplified model which includes equal couplings between all N spins of a system. The same model is used to compare the merits of different forms of ‘‘high temperature’’ approximation. We also propose an iterative scheme for solving the ‘‘modified Bloch...

Radiation damping in high resolution liquid NMR: A simulation study

Radiation damping generates surprising new features in two‐dimensional and spin–echo experiments. The theoretical interpretation of the unexpected results has led to some controversy. The purpose of the present paper is to show, by computer simulations, that the experimental results can be completely understood by describing radiation damping through a classical magnetic field caused by the current induced in the sample coil (resonantly enhanced by the high quality factor of the tuned circuit), and acting back on the spins. We examine a variety of two‐dimensional and ‘‘multiple quantum’’ experiments in homogeneous fields, and spin‐echo experiments in a fixed field gradient (with and without molecular diffusion).

Equivalence between the “classical” and the “Warren” approaches for the effects of long range dipolar couplings in liquid nuclear magnetic resonance

I show, on a simple example, that the two approaches lead to exactly the same density operator for the whole spin system, with the same equations of motion for the matrix elements (ignoring relaxation and diffusion). Hence, the two approaches are equivalent in all respects.

Dynamical instabilities in liquid nuclear magnetic resonance experiments with large nuclear magnetization, with and without pulsed field gradients

In this article we extend previous studies of the dynamical instabilities to incorporate the roles of the tipping angle, the overall shape of the sample, (optional) pulsed field gradients in various directions, and radiation damping. The linear stability for small perturbations is discussed analytically in detail, and numerical simulations are used to have a glimpse at the turbulent spin motion for large perturbations.

Low Temperature Mixing Calorimeter for Liquids

A technique is described for measuring the heat of mixing, excess volume, specific heat, and other thermodynamic properties of liquid systems at low temperature (e.g., CO, CH4, A, Kr). Experiments are carried out at constant pressure, without any vapor phase in the calorimetric vessel.

A presentation of pulsed nuclear magnetic resonance with full quantization of the radio frequency magnetic field

We show that there is excellent quantitative agreement between the usual semiclassical predictions for nuclear magnetic resonance experiments (quantized spins interacting with a classical radio frequency magnetic field, including radiation damping), and the predictions of a fully quantized description of the same experiment. We also propose a pictorial description of the relevant dynamical quantum states, which helps to lead the intuition towards the same conclusion. Our model ignores spin relaxation, and simulates the equivalent damping resistor of the sample circuit by a very long piece of lossless coaxial cable. The classical rf field (pulses and free induction decay) is described quantum mechanically by means of Glauber’s “coherent” or “quasiclassical” states.

Comment on “Diffusion measurements with the pulsed gradient nonlinear spin echo method” [J. Chem. Phys. 112, 5275 (2000)]

An undocumented approximation has been found in the discussion of the effects of molecular diffusion in the CRAZED experiment, as presented in the reference quoted in the title. A detailed discussion shows the subtle origin of the problem. Reference is given to discussions which avoid this approximation by using the extended Bloch equation.

Confinement effects on dipole–dipole interactions in nanofluids: The role of equilibrium fluctuations

When spin bearing molecules are enclosed in an elongated nanovoid, and each molecule diffuses across the whole volume in times much shorter than the characteristic times of NMR spin dynamics, a time independent average dipolar Hamiltonian emerges which couples the spins in each molecule equally with the spins in any other molecule. Baugh et al. [Science, 134, 1505 (2001)] have observed the remarkable orientation dependent linewidth in such a situation, and offered a convincing interpretation using the techniques of solid state NMR. In the present paper I show that, contrary to previous expectations, the same linewidth can be predicted with liquid NMR techniques, provided that one takes into account equilibrium fluctuations in the estimation of the dipolar field.

Reply to comment on Multiple quantum coherences in liquid state NMR and nonlinear optics; collective vs. local origin (Chem. Phys. Lett. 357 (2002) 327)

The present Comment points out inconsistencies in this Letter, concerning the origin and the standard interpretation of multiple quantum coherences in liquid state NMR.