Eric G. Sorte

Collisional 3He and 129Xe frequency shifts in Rb-noble-gas mixtures.

The Fermi-contact interaction that characterizes collisional spin exchange of a noble gas with an alkali-metal vapor also gives rise to NMR and EPR frequency shifts of the noble-gas nucleus and the alkali-metal atom, respectively. We have measured the enhancement factor κ0 that characterizes these shifts for Rb-129Xe to be 493±31, making use of the previously measured value of κ0 for Rb-3He. This result allows accurate 129Xe polarimetry with no need to reference a thermal-equilibrium NMR signal.

Long-time behavior of nuclear spin decays in various lattices

The transverse NMR decays of {sup 129}Xe in polycrystalline xenon were recently shown to have a universal property: in the long-time regime these decays all converge to the same sinusoidally modulated exponential function irrespective of the initial transverse spin configuration prepared by a sequence of one or more radio frequency pulses. The present work constitutes a more comprehensive survey of this phenomenon. It examines transverse decays for several different isotopic concentrations of {sup 129}Xe, employs additional pulse sequences, and performs similar measurements in a different material: {sup 19}F in single-crystal and polycrystalline CaF{sub 2}. With the possible exception of polycrystalline CaF{sub 2} where the observation of the long-time behavior is limited by the experimental resolution, all these systems display the long-time universal behavior characterized by particular values of the exponential decay coefficient and beat frequency that were unique for each lattice. This behavior has been theoretically predicted based on the notion of microscopic chaos.

Methanol and Ethanol Electrooxidation on PtRu and PtNiCu as Studied by High-Resolution In Situ Electrochemical NMR Spectroscopy with Interdigitated Electrodes

Following a recent short communication (J. Electroanal. Chem. 769 (2016) 1–4) in which we demonstrated the feasibility and proof-of-concept results of using interdigitated metal electrodes to achieve high-resolution in situ electrochemical solution NMR for studying electrochemically driven reactions such as those involved in electrolysis and electrocatalysis, we report herein a more detailed technical description of the technique and its application to studying methanol and ethanol electrooxidation on PtRu and PtNiCu electrocatalysts.Graphical Abstract13C NMR data from ethanol oxidation with a PtNiCu catalyst. (a) C NMR resonances as a function of time, showing the growth of all product peaks. (b) Comparison of the final spectra of ethanol oxidation reactions performed with PtNiCu (black, upper) and PtRu (blue, lower) catalysts. Differences in the relative intensities of the product peaks can be identified.

Phase relationship between the long-time beats of free induction decays and spin echoes in solids

Recent theoretical work on the role of microscopic chaos in the dynamics and relaxation of many-body quantum systems has made several experimentally confirmed predictions about the systems of interacting nuclear spins in solids, focusing, in particular, on the shapes of spin echo responses measured by nuclear magnetic resonance (NMR). These predictions were based on the idea that the transverse nuclear spin decays evolve in a manner governed at long times by the slowest decaying eigenmode of the quantum system, analogous to a chaotic resonance in a classical system. The present paper extends the above investigations both theoretically and experimentally. On the theoretical side, the notion of chaotic eigenmodes is used to make predictions about the relationships between the long-time oscillation phase of the nuclear free induction decay (FID) and the amplitudes and phases of spin echoes. On the experimental side, the above predictions are tested for the nuclear spin decays of F-19 in CaF2 crystals and Xe-129 in frozen xenon. Good agreement between the theory and the experiment is found.

Asymptotic and intermediate long-time behavior of nuclear free induction decays in polycrystalline solids and powders.

Abstract Free induction decay (FID) measured by nuclear magnetic resonance (NMR) in a polycrystallinesolid is the isotropic average of the FIDs for individual single crystallites. It has been recently pro-posed theoretically and verified experimentally that the long-time behavior of single-crystal FIDshas the universal form of exponentially decaying sinusoidal oscillations. Polycrystalline averagingcomplicates the situation theoretically, while the available experimental evidence is also ambigu-ous. Exponentially decaying sinusoidal oscillations have been observed for 129 Xe in polycrystallinesolid xenon but not for 19 F in the powder of CaF 2 . In this paper, we present the first principlesFID calculations for the powders of both CaF 2 and solid xenon. In both cases, the asymptoticlong-time behavior has the expected form of exponentially decaying sinusoidal oscillations, which isdetermined by the single crystallite FID with the slowest exponential decay. However, this behaviorappears only at rather small values of the signal that have not yet been measured in experiments.At intermediate times accessible experimentally, a polycrystalline FID depends on the distributionof the exponential decay constants and oscillation frequencies for single crystallite FIDs. In CaF