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: In this paper, the in-phase and out-of-phase properties of a spin glass were investigated and it was shown that the properties of spin glass have a broad spectrum of relaxation times.
141 citations
TL;DR: In this paper, a detailed comparison with THz time domain spectroscopy demonstrates that the reorientational dynamics responsible for the long time tail of the Kerr response are due to single molecule as opposed to collective effects.
Abstract: The ultrafast optical Kerr-response of water and heavy water has been measured at 1 bar in the temperature range between 273 and 373 K. The nuclear Kerr response of the liquid exhibits a pronounced double exponential decay on longer time scales after dephasing of impulsively perturbed acoustic modes is completed. The time constant, τ2, characterizing the slowly decaying exponential component of the Kerr-response function is in quantitative agreement with rotational diffusion time constants of the water molecules obtained form nuclear magnetic resonance (NMR) spin-lattice relaxation rates. A detailed comparison with THz time domain spectroscopy demonstrates that the reorientational dynamics responsible for the long time tail of the Kerr response are due to single molecule as opposed to collective effects. Furthermore, a good agreement between the single molecule rotational diffusion and the Stokes–Einstein–Debye equation is found in the temperature range of thermodynamic stability of the liquid. The time constant, τ1, characterizing the fast exponential component of the Kerr-response of water is found to be in qualitative agreement with central Lorentzian linewidths obtained from frequency-domain, depolarized Raman scattering experiments. The temperature dependence of τ2 does not follow an Arrhenius-type behavior, which was previously taken as evidence for thermally activated crossing of a librational barrier with concomitant hydrogen-bond breakage. Instead, the temperature dependence of the fast relaxation time constant can be represented adequately by the Speedy–Angell relation which has been shown to accurately describe a number of transport parameters and thermodynamic properties of water.
141 citations
TL;DR: In this article, the presence or absence of intramolecular vibrational relaxation (or more precisely state mixing) from an excited C-H stretch in 23 representative molecules varying in size from methane to nonbornene.
Abstract: Infrared fluorescence measurements have been used to determine the presence or absence of intramolecular vibrational relaxation (or more precisely state mixing) from an excited C–H stretch in 23 representative molecules varying in size from methane to nonbornene. Included are aliphatic hydrocarbons, aromatic molecules, ethers, and ketones, including cyclic molecules. The rate of resonance fluorescence, calculated relative to a nonrelaxing molecule, was used as the criterion of relaxation. Small rates imply state mixing and hence in the large molecule limit, relaxation. The primary correlation with the presence of mixing is with state density; about ten states per wave number (cm−1) are needed to insure mixing. The spread in threshold densities reflects variations in anharmonicity. For some molecules true relaxed (non C–H stretch) fluorescence is observed. These experiments were done in a molecular beam, using a pulsed optical parametric oscillator for excitation and a circular variable filter for spectral...
141 citations
TL;DR: In this paper, a theroy relating rotational Brownian motion to the time autocorrelation function of the intensity of radiation from a fluorescent system composed of spherical rotors is presented.
Abstract: A theroy relating rotational Brownian motion to the time autocorrelation function of the intensity of radiation from a fluorescent system composed of spherical rotors is presented. The calculation shows three relaxation times, two associated with the rotational diffusion, and the third associated with the natural decay of the fluorescence. The correlation function contains terms that relax independently of the fluorescence decay time, thus arbitrarily extending the time range over which rotational diffusion can be studied by fluorescence.
140 citations
TL;DR: Steady SSFP imaging during the transient phase can provide various contrasts depending on the flip angle and the number of excitation pulses applied before the acquisition of the central k‐space line, and hyperpolarized nuclei can be optimized according to their T1 and T2 relaxation times.
Abstract: The signal intensity of balanced steady-state free precession (SSFP) imaging is a function of the proton density, T(1), T(2), flip angle (alpha), and repetition time (TR). The steady-state signal intensity that is established after about 5*T(1)/TR can be described analytically. The transient phase or the approach of the echo amplitudes to the steady state is an exponential decay from the initial amplitude after the first excitation pulse to the steady-state signal. An analytical expression of the decay rate of this transient phase is presented that is based on a simple analysis derived from the Bloch equations. The decay rate is a weighted average of the T(1) and T(2) relaxation times, where the weighting is determined by the flip angle of the excitation pulses. Thus, balanced SSFP imaging during the transient phase can provide various contrasts depending on the flip angle and the number of excitation pulses applied before the acquisition of the central k-space line. In addition, transient imaging of hyperpolarized nuclei, such as (3)He, (129)Xe, or (13)C, can be optimized according to their T(1) and T(2) relaxation times.
140 citations