Topic
Relaxation (NMR)
About: Relaxation (NMR) is a research topic. Over the lifetime, 29342 publications have been published within this topic receiving 689851 citations.
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TL;DR: The steady-state and ultrafast vibrational spectroscopy of dilute HOD in aqueous solutions of sodium bromide is studied, finding that spectral diffusion is very complicated, with processes occurring on multiple time scales.
Abstract: We study theoretically the steady-state and ultrafast vibrational spectroscopy, in the OD-stretch region, of dilute HOD in aqueous solutions of sodium bromide. Based on electronic-structure calculations on clusters containing salt ions and water, we develop new spectroscopic maps that enable us to undertake this study. We calculate OD-stretch absorption line shapes as a function of salt concentration, finding good agreement with experiment. We provide molecular-level understandings of the monotonic (as a function of concentration) blueshift, and nonmonotonic line width. We also calculate the frequency time-correlation function, as measured by spectral diffusion experiments. Here again we obtain good agreement with experiment, finding that at the highest salt concentration spectral diffusion slows down by a factor of 3 or 4 (compared to pure water). For longer times than can be accessed experimentally, we find that spectral diffusion is very complicated, with processes occurring on multiple time scales. We argue that from 6 to 40 ps, relaxation involves anionic solvation shell rearrangements. Finally, we consider our findings within the general context of the Hofmeister series, concluding that this series must reflect only local ordering of water molecules.
132 citations
01 Jan 2012
TL;DR: In this article, the magnetism of DySc2N@C80 endoful lerene was studied with X-ray magnetic circular dichroism (XMCD) and a magnetometer with a superconducting quantum interference device (SQUID) down to temper- atures of 2 K and in fields up to 7 T.
Abstract: The magnetism of DySc2N@C80 endoful- lerene was studied with X-ray magnetic circular dichroism (XMCD) and a magnetometer with a superconducting quantum interference device (SQUID) down to temper- atures of 2 K and in fields up to 7 T. XMCD shows hysteresis of the 4f spin and orbital moment in Dy III ions. SQUID magnetometry indicates hysteresis below 6 K, while thermal and nonthermal relaxation is observed. Dilution of DySc2N@C80 samples with C60 increases the zero-field 4f electron relaxation time at 2 K to several hours.
132 citations
TL;DR: In this paper, the authors measured and analyzed the dynamic mechanical response of polybutadienes with molecular weights from 20000 to 200000, and the results indicated that the two types of polymers have a similar relaxation pattern.
Abstract: The relaxation behavior of polymers with long linear flexible chains of uniform length has been investigated by means of dynamic mechanical analysis. The relaxation time spectrum (H(λ)) follows a scaling relationship with two self-similar regions, one for the entanglement and terminal zone, and a second one for the transition to the glass. This can be described in its most general form (termed “BSW spectrum”) as H(λ) = H
e
λne
+ H
g
λ−
n
g
for λ < λmax and H(λ) = 0 for λmax < λ, where H
e
, H
g
, n
e
, n
g
are material constants and λmax is the molecular weight dependent cut-off of the self-similar behavior. In this study, the dynamic mechanical response has been measured and analyzed for four highly entangled, nearly monodisperse polybutadienes with molecular weights from 20000 to 200000. The data are well represented by the BSW spectrum with scaling exponents of n
e
= 0.23 and n
g
= 0.67. The values of the exponents obtained in this work are about the same as those found for polystyrene samples in a previous study. This suggests that the two types of polymers have a similar relaxation pattern. However, at this point further refinement of the experiments is needed before being able to draw definite conclusions about the universality of the exponents.
132 citations
TL;DR: In this paper, the variable nutation angle (VNA) method was evaluated for the measurement of NMR spin-lattice relaxation times and the sensitivity of the deduced T1′s to these conditions was explored.
132 citations
TL;DR: It is shown experimentally and theoretically that slow relaxation of the magnetization can still be observed in the AF phase, with a maximum of the relaxation time close to the AF-paramagnetic phase transition.
Abstract: A system presenting an antiferromagnetic (AF) phase of Single-Chain Magnets (SCMs) is studied at low temperatures. The phase diagram is first discussed to specify the magnitude of the interchain couplings. Then, we show experimentally and theoretically that slow relaxation of the magnetization can still be observed in the AF phase, with a maximum of the relaxation time close to the AF-paramagnetic phase transition. This counter intuitive result shows that materials presenting such an ordered state can be used to design high temperature magnets using SCM-based materials.
132 citations