622 research outputs found
A new Raman technique of superior spectral resolution
Raman-active vibrational modes are coherently excited by the transient stimulated Raman process. A subsequent delayed probe of relatively long duration interacts with the freely relaxing vibrations. Raman spectra are generated with higher resolution and more accurate peak positions than in conventional Raman spectroscopy. In liquid cyclohexane four new Raman lines were readily detected in the frequency range 2870–2920 cm−1
Characterization of the Dynamics of Glass-forming Liquids from the Properties of the Potential Energy Landscape
We develop a framework for understanding the difference between strong and
fragile behavior in the dynamics of glass-forming liquids from the properties
of the potential energy landscape. Our approach is based on a master equation
description of the activated jump dynamics among the local minima of the
potential energy (the so-called inherent structures) that characterize the
potential energy landscape of the system. We study the dynamics of a small
atomic cluster using this description as well as molecular dynamics simulations
and demonstrate the usefulness of our approach for this system. Many of the
remarkable features of the complex dynamics of glassy systems emerge from the
activated dynamics in the potential energy landscape of the atomic cluster. The
dynamics of the system exhibits typical characteristics of a strong supercooled
liquid when the system is allowed to explore the full configuration space. This
behavior arises because the dynamics is dominated by a few lowest-lying minima
of the potential energy and the potential energy barriers between these minima.
When the system is constrained to explore only a limited region of the
potential energy landscape that excludes the basins of attraction of a few
lowest-lying minima, the dynamics is found to exhibit the characteristics of a
fragile liquid.Comment: 13 pages, 6 figure
An Experimental and Theoretical Investigation of the Skeletal Frequencies of the Paraffin Hydrocarbons and the Far Infra‐Red Spectrum of Carbon Tetrachloride
The far infra‐red spectra of the paraffin hydrocarbons and of carbon tetrachloride have been investigated. The following bands were located: propane at 370.6 cm−1, n‐butane at 215 cm−1, and carbon tetrachloride at 315 cm−1, the latter showing isotope structure. The contours of the following near infra‐red bands for n‐butane were surveyed, and some fine structure was revealed: 1342.9 cm−1, 1295.6 cm−1, 1135.6 cm−1, 956.5 cm−1, and 740.0 cm−1. The assignment of the skeletal frequencies of vibration is made, and a theoretical analysis of the skeletal normal frequencies, assuming a valence potential for the molecules propane through pentane, is given.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/71089/2/JCPSA6-17-4-393-1.pd
Rotational Brownian motion on the sphere surface and rotational relaxation
The spatial components of the autocorrelation function of noninteracting
dipoles are analytically obtained in terms of rotational Brownian motion on the
surface of a unit sphere using multi-level jumping formalism based on Debye's
rotational relaxation model, and the rotational relaxation functions are
evaluated.Comment: RevTex, 4 pages, submitted to Chin. Phys. Let
Twist glass transition in regioregulated poly(3-alkylthiophenes)s
The molecular structure and dynamics of regioregulated poly(3-butylthiophene)
(P3BT), poly(3-hexylthiophene)(P3HT), and poly(3-dodecylthiophene) (P3DDT) were
investigated using Fourier transform infrared absorption (FTIR), solid state
C nuclear magnetic resonance (NMR), and differential scanning
calorimetry (DSC) measurements. In the DSC measurements, the endothermic peak
was obtained around 340 K in P3BT, and assigned to enthalpy relaxation that
originated from the glass transition of the thiophene ring twist in crystalline
phase from results of FTIR, C cross-polarization and magic-angle
spinning (CPMAS) NMR, C spin-lattice relaxation time measurements, and
centerband-only detection of exchange (CODEX) measurements. We defined this
transition as {\it twist-glass transition}, which is analogous to the plastic
crystal - glassy crystal transition.Comment: 9 pages, 10 figures, 2 tables. Phys.Rev.B, in pres
The Infra‐Red Absorption Spectrum of Propane
Of the twenty‐seven internal degrees of freedom of propane, all nondegenerate, twenty‐two may appear as fundamental absorption bands. These bands fall into three symmetry classes, designated A1, B1 and B2, and distinguishable by their characteristic contours. Because of overlapping, however, it is impossible in many cases to determine their positions precisely. This is especially true in the regions of the C☒H valence and deformation frequencies. Some ten or twelve fundamental bands may be identified with confidence as well as a number of combinations. An A1 band at 870 cm—1 and a B2 band at 748 cm—1 have been partially resolved, the line spacing being about 1.47 cm—1 in agreement with predictions based upon electron diffraction measurements. The fine structure of the B1 bands has not been observed (the predicted spacing is 0.5 cm—1) but the interval between maxima of the P and R branches is approximately 26 cm—1 as expected. With 24 cm‐atmospheres of gas no bands were observed between 15μ and 35μ, although the symmetrical C☒C deformation might be expected to produce a band of appreciable intensity within these limits. This frequency has apparently been observed in Raman spectra at 375 cm—1.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/70815/2/JCPSA6-9-7-487-1.pd
Relaxation properties in a lattice gas model with asymmetrical particles
We study the relaxation process in a two-dimensional lattice gas model, where
the interactions come from the excluded volume. In this model particles have
three arms with an asymmetrical shape, which results in geometrical frustration
that inhibits full packing. A dynamical crossover is found at the arm
percolation of the particles, from a dynamical behavior characterized by a
single step relaxation above the transition, to a two-step decay below it.
Relaxation functions of the self-part of density fluctuations are well fitted
by a stretched exponential form, with a exponent decreasing when the
temperature is lowered until the percolation transition is reached, and
constant below it. The structural arrest of the model seems to happen only at
the maximum density of the model, where both the inverse diffusivity and the
relaxation time of density fluctuations diverge with a power law. The dynamical
non linear susceptibility, defined as the fluctuations of the self-overlap
autocorrelation, exhibits a peak at some characteristic time, which seems to
diverge at the maximum density as well.Comment: 7 pages and 9 figure
Anomalous Rotational Relaxation: A Fractional Fokker-Planck Equation Approach
In this study we obtained analytically relaxation function in terms of
rotational correlation functions based on Brownian motion for complex
disordered systems in a stochastic framework. We found out that rotational
relaxation function has a fractional form for complex disordered systems, which
indicates relaxation has non-exponential character obeys to
Kohlrausch-William-Watts law, following the Mittag-Leffler decay.Comment: Revtex4, 9 pages. Paper was revised. References adde
Relation between positional specific heat and static relaxation length: Application to supercooled liquids
A general identification of the {\em positional specific heat} as the
thermodynamic response function associated with the {\em static relaxation
length} is proposed, and a phenomenological description for the thermal
dependence of the static relaxation length in supercooled liquids is presented.
Accordingly, through a phenomenological determination of positional specific
heat of supercooled liquids, we arrive at the thermal variation of the static
relaxation length , which is found to vary in accordance with in the quasi-equilibrium supercooled temperature regime, where
is the Vogel-Fulcher temperature and exponent equals unity. This
result to a certain degree agrees with that obtained from mean field theory of
random-first-order transition, which suggests a power law temperature variation
for with an apparent divergence at . However, the phenomenological
exponent , is higher than the corresponding mean field estimate
(becoming exact in infinite dimensions), and in perfect agreement with the
relaxation length exponent as obtained from the numerical simulations of the
same models of structural glass in three spatial dimensions.Comment: Revised version, 7 pages, no figures, submitted to IOP Publishin
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