A. Wokaun

Selective detection of multiple quantum transitions in NMR by two-dimensional spectroscopy

Abstract A technique is described for the selective detection of multiple quantum transitions by means of two-dimensional spectroscopy. The separation of various orders of transitions is based on characteristic transformation properties of multiple quantum transitions permitting an orthogonal expansion of the response function.

Coherence transfer echoes

Abstract A novel class of echo phenomena in coherent spectroscopy is described where defocusing and refocusing of coherence takes place at two different transition frequencies. Examples of heteronuclear transfer echoes and of multiple quantum transfer echoes in nuclear magnetic resonance are presented.

The use of multiple quantum transitions for relaxation studies in coupled spin systems

The utility of multiple quantum transitions is discussed with regard to the elucidation of relaxation mechanisms in coupled spin systems. The information contained in the decay rates of multiple quantum coherence is analysed in terms of the Redfield formalism, and experimental schemes suitable for their measurement are presented. As an illustration, external paramagnetic relaxation in a two-spin system is investigated, based on measured multiple and single quantum relaxation rates.

Pulse techniques applied to chemically induced dynamic nuclear polarization

Abstract The application of pulse techniques for the creation and investigation of chemically induced dynamic nuclear polarization is described. Pulsed optical excitation in combination with pulse Fourier experiments offers possibilities of measuring absolute CIDNP intensities unperturbed by relaxation effects, eliminating background signals, and investigating secondary chemical reactions. The effects of relaxation in CIDNP are analyzed.

Study of transient chemical reactions by NMR. Fast stopped-flow fourier transform experiments

Abstract The theoretical formalism for the treatment of magnetic resonance in the presence of nonequilibrium chemical reactions is presented. It is applied to the study of fast transient chemical reactions by means of NMR Fourier experiments. The main emphasis is put on the analysis of the lineshape. It is found that for transient reactions characteristic lineshapes occur which are qualitatively different from those well known for dynamic chemical equilibria. Experimental results using fast stopped-flow mixing techniques are described. The kinetic deuterium isotope effect in the hydrolysis of methyl formate is studied.

Sensitivity of two-dimensional NMR spectroscopy

Abstract The sensitivity of two-dimensional NMR Fourier spectroscopy is analyzed and compared with the sensitivity of one-dimensional Fourier spectroscopy. It is confirmed by experiment that as little as a factor 2 may be lost by going from 1D to 2D spectroscopy.

The creation of off-diagonal elements in chemically induced dynamic nuclear polarization experiments

Abstract The nuclear density matrix created in pulsed CIDNP experiments contains off-diagonal elements whenever the resulting nuclear spin system is strongly coupled. These off-diagonal elements, which connect spin states with the same magnetic quantum number, are due to the mixing of nuclear state functions during the process of product formation. The observation of these elements by means of a two-pulse experiment is described.

Multiple quantum double resonance

A theoretical description of double resonance effects on multiple quantum N.M.R. transitions is presented. In particular, multiple quantum tickling phenomena are analysed. The results are confirmed by experiment.

Theory of stochastic NMR spectroscopy. Application of the ITÔ and Stratonovich calculus

Abstract The theory of stochastic differential equations is used to give a new description of a stochastic NMR experiment. It replaces an earlier approach, which was based on Wieners orthogonal expansion of the stochastic response. For the first time, the saturation behaviour in cross and power spectra is predicted correctly. A numerical experiment confirms the theoretical results. The relative signal intensities in a stochastic resonance spectrum are calculated and compared with those obtained in a slow passage experiment. Conditions for equal relative intensities are given for various experimental situations.