Localization Of Vibrational Energy Research Articles

Breathers or Structural Instability in Solid L-Alanine: a New IR and Inelastic Neutron Scattering Vibrational Spectroscopic Study

Incoherent Inelastic Neutron Scattering data and new infrared spectra were acquired in order to examine both the external and internal vibrations in crystalline L-alanine. For the first time we observe a splitting of the NH3+ torsional band below a temperature of approximately 220 K as well as an overtone of this band. The intensity of both of these bands is strongly dependent on temperature. Birefringence and depolarization measurements performed with single crystals reveal a subtle breaking of symmetry around 220 K perhaps involving the hydrogen bond networks. We show that this instability cannot, however, be the origin of the observed splitting. Instead, the anomalous temperature dependence of the observed intensity and frequency of the torsional mode and its overtone may be explained on the basis of a nonlinear coupling of the NH3+ oscillator with lattice phonons. This leads to localization of vibrational energy, a so-called “breather” or “vibrational polaron”.

Nonequilibrium processes for generating silicon nanostructures in single-crystalline silicon

Abstract The possibility of modifying existing materials through technology has become the recipe for preparation of advanced materials. Nonequilibrium processing of silicon through MeV ion irradiation will be shown here to yield interesting properties. We propose localization of vibrational energy following an ion irradiation process and their transport (nonlinear transport of energy) through linear chains of a single-crystalline lattice. The localization of energy can involve 3­4 atoms, and, hence, nanometer-sized entities evolve, distinguishable from the remaining periodic lattice owing to their unique interatomic distances. The energy required to produce these structures is supplied by a single high-energy heavy ion, incident normal to a suitable crystal face so as to lose energy by the electronic energy loss mechanism. These entities can be trapped at a desired location that leads to silicon nanostructures with modified band-gaps.

Modulational instability and energy localization in anharmonic lattices at finite energy density

The localization of vibrational energy, induced by the modulational instability of the Brillouin-zone-boundary mode in a chain of classical anharmonic oscillators with finite initial energy density, is studied within a continuum theory. We describe the initial localization stage as a gas of envelope solitons and explain their merging, eventually leading to a single localized object containing a macroscopic fraction of the total energy of the lattice. The initial-energy-density dependences of all characteristic time scales of the soliton formation and merging are described analytically. Spatial power spectra are computed and used for the quantitative explanation of the numerical results.

Vibrational energy localization in the stretching vibrational (1000A1/F2), (2000A1/F2), and (3000A1/F2) band systems of SnD4120

High resolution Fourier transform infrared spectra of the stretching fundamental (1000A1/F2) as well as the first (2000A1/F2) and second (3000A1/F2) stretching vibrational overtones of monoisotopic deuterated stannane, SnD4120, were measured using a Bruker 120 HR interferometer. The symmetric top K structure of a prolate symmetric rotor was observed in the second stretching vibrational overtone, which indicates that localization of vibration has occurred and the dynamic symmetry of the molecule has changed. Rotational analyses of the spectra were performed, and the local mode relations obtained confirm that vibrational energy localization takes place in the second stretching vibrational overtone of deuterated stannane. The results indicate a surprisingly similar behavior of deuterated stannane and normal stannane.

Spontaneous Localization of Vibrational Energy

In this paper we illustrate a number of the characteristic manifestations of soft anharmonicity in the behavior of lattice vibrations, both in and out of thermal equilibrium. In particular, we focus on various ways in which vibrational energy may come to be localized as a consequence of anharmonicity, even in defect-free lattices. These include the overpopulation of anharmonic vibrations in thermal equilibrium, the inhibition of dispersion, and the enhancement of spatial coherence. The relevance of the spontaneous localization of vibrational energy in the formation of hot spots is discussed, with particular emphasis on the unstable evolution of high-amplitude initial conditions as may be found in initiating shocks.

Localization of vibrational energy in globular protein

The discrete self-trapping (DST) equation is used to model the amide I vibrations of a globular protein. The influence of anharmonic effects on localization of the amide I energy is investigated, in particular the competition between Anderson localization and nonlinear localization.

Vibrational mode mixing in terminal acetylenes: High-resolution infrared laser study of isolated J states

Mode–mode vibrational coupling in the acetylinic CH stretch at 3330 cm−1 of 1-butyne and 1-pentyne is studied via high-resolution, direct absorption infrared spectroscopy. As in our previous study of propyne, mixing of the CH stretch vibration carrying oscillator strength (the bright state) with the bath of multiquantum combination states (the dark, or background, states) manifests itself in the spectrum via fragmentation of the isolated bright state transitions into clusters of closely spaced spectral lines in a ∼0.01 cm−1 window about the zeroth order acetylinic CH stretch position. In the 1-butyne spectrum, we find an experimental density of mixed states of 114±30 states/cm−1 compared to a direct state count prediction of 90 total states/cm−1, and thus quantitatively determine that all possible states appear in the spectrum. The 1-butyne line spacing distribution suggests the Wigner distribution expected for a quantum mechanically ergodic system. Analysis of the mode mixing as a function of J′ shows that anharmonic terms in the potential, rather than Coriolis effects, contribute most strongly to the coupling. The acetylinic CH stretch spectrum of 1-pentyne (2400 states/cm−1) reveals only broad rovibrational transitions with ∼0.01 cm−1 Lorentzian width, even at our 10−4 cm−1 resolution. J′ independent, anharmonic coupling with a minimum of 1/3 of all states must be invoked to reproduce the observed broadening. In contrast, the 1-pentype methyl CH stretch spectrum shows broadening greater than five times larger than that observed at the acetylinic end. Via Fourier transform methods, the spectra for both 1-butyne and 1-pentyne indicate vibrational energy localization in the CH stretch for ∼500 ps. However, for the methyl CH stretch, energy redistribution takes place in <40 ps, clearly indicating the presence of mode specific, nonRRKM vibrational relaxation pathways.

Anomalous temperature dependence in the Raman spectra of l-alanine: Evidence for dynamic localization.

We measured the temperature dependence of the intensity of the two lowest Raman modes in single crystals of l-alanine. The sum of the intensities obeys Maxwell-Boltzman statistics accurately from 20 to 340 K but the intensities of the individual lines are anomalous. This behavior is explained by assuming that both lines share the same degrees of freedom but that a mode instability is triggered abruptly at an occupation of seven quanta. This instability, which has an activation energy of 500 K, is observed at temperatures as low as 20 K, possibly indicating the existence of dynamic localization of vibrational energy.

The nature of anomalous temperature dependence of photoluminescence in glasses

The anomalouos temperature dependence of photoluminescence (PL) in glasses is related to local increase in temperature around the PL center. The temperature increases due to induced by disorder localization of vibration energy which arises together with the Stokes shift. In the frames of this model some experimental results on PL are explained.

On vibrational energy localization at high levels of excitation. Vibrational excitons

This review discusses the properties of highly excited vibrational states of polyatomic molecules and molecular crystals. As we know, one can describe small vibrations of molecules with the concept of normal modes. In molecules having several identical valence bonds (C6H6, H2O, etc.) the normal modes that describe the vibrational excitations of these bonds amount to vibrations whose energy is more or less uniformly distributed over all the bonds, with a degree of delocalization of the energy over the bonds that increases with increasing level of excitation. On the other hand, an extensive set of physical phenomena exists (e.g., dissociation of molecules) in which local excitations, a considerable fraction of which are spatially localized, play an important role. A localized state corresponds to a complicated superposition of normal modes. Hence the concept of normal vibrations is inadequate for describing vibrations (or, better expressed, movements) of a highly excited molecule. One can conveniently describe such movements of the molecule in the representation of local modes (LM). As a rule, one takes an LM to mean simply the coordinate of a valence bond of the molecule, e. g., O–H, C–H, etc. A large number of papers has been published recently on the experimental study of LM and infrared spectra, relaxation experiments, selective photochemistry, etc. This review casts light on these experimental data on the basis of the theory of LM.

O lokalizatsii kolebatel'noi energii pri vysokikh urovnyakh vozbuzhdeniya. Kolebatel'nye eksitony

О локализации колебательной энергии при высоких уровнях возбуждения. Колебательные экситоны, Овчинников А.А., Эрихман Н.С.

Predissociation probes of vibrational energy localization

Ring-bound van der Waals complexes of the alkylbenzenes are studied.(AIP)

Some symmetry aspects of the local‐mode description of vibrational structure

AbstractIn the local‐mode description of vibrational structure, the nuclear coordinates—unlike the usual normal coordinates—do not reflect the molecular symmetry. Accordingly, the local‐mode product wave functions must be symmetry adapted. We discuss this simple procedure in light of its implications for the localization of vibrational energy and the dissociation limits of molecular excited states. These properties are in turn related to the separability of the total nuclear Hamiltonian and to the different ways in which the vibrational anharmonicity is “absorbed” by the local and normal coordinates.