Universal nonexponential relaxation: Complex dynamics in simple liquids

Abstract

Structural relaxation in the hydrogen-bonding liquids -methylacetamide and water studied by optical Kerr effect spectroscopy

Rattling the cage: Micro- to mesoscopic structure in liquids as simple as argon and as complicated as water

“…The signals have been rescaled (to the argon signal) to show that -despite the different properties of atomic mass, size, and polarizability -the decay function for the three atomic liquids is identical within the signal-to-noise ratio except for a pair of amplitude and frequency scaling parameters. [73] At times t/t x > 1.5 ps the decay measured is consistent with the derivative of the stretched-exponential function…”

“…For temperature dependent experiments, the samples were condensed into sealed glass cuvettes held in a cryostat (Oxford Instruments, Optistat DN). [73] Typical OKE data in the time domain is shown in Fig. 2 on double logarithmic axes.…”

“…[105][106][107] We have studied the noble-gas liquids of argon, krypton, and xenon under the initial assumption that the dynamics would be extremely simple. [73] OKE spectroscopy (as well as anisotropic Raman scattering) is sensitive to rotation of the polarizability tensor. [46,49] The only anisotropy in the polarizability tensor of atomic liquids comes from collision-induced effects.…”

Methyl group rotation, 1H spin-lattice relaxation in an organic solid, and the analysis of nonexponential relaxation

“…65,66 It has found use in interpreting neutron scattering experiments, 67,68 Kerr-effect spectroscopy in liquids, 69 studies of glass-forming liquids, 70 dielectric relaxation, [71][72][73][74][75] luminescence spectroscopy, 76,77 linear dichroism correlation spectroscopy, 78 lipid bilayer dynamics, 79 NMR spinlattice relaxation in a random Heisenberg chain, 80 light scattering, 74,75 ion conductivity measurements, 81 NMR studies of ion conduction, 82,83 photobleaching relaxation, 84 and various forms of structural relaxation. 85,86 It is not straightforward to relate the parameters R* and β to the dynamics.…”

“…The cases of β = 2/3, 1/2, and 1/3 have been investigated very thoroughly and the distribution of exponential relaxation rates can be expressed in closed form using gamma functions and generalized hypergeometric functions. 88,89 For β < 1, the stretched-exponential function is unphysical at short times, 65,70,71,76,77 or, equivalently, at high frequencies 69,71 and this can be addressed by phenomenologically multiplying it by the appropriate function 65,69,71 or by shifting the time origin. 76,77 Our NMR relaxation experiments do not involve times short enough for this to be a problem.…”