Characterization of non-lorentzian line shapes in atom-atom collisions

1982 ◽  
Vol 1 (3) ◽  
pp. 442-448 ◽  
Author(s):  
J. S. Dehesa
Keyword(s):  
Lorentzian Line ◽  
Line Shapes

Potentialities of an Innovative Technique Like 129Xe NMR and of Saxs for the Characterization of Microporous Sol-Gel Derived SiO2

1996 ◽  
Vol 431 ◽  
Author(s):  
L. C. de Menorval ◽  
A. Julbe ◽  
H. Jobic ◽  
J. A. Dalmon ◽  
C. Guizard
Keyword(s):  
Chemical Shifts ◽  
High Surface ◽  
Sol Gel ◽  
Narrow Pore Size Distribution ◽  
X Ray ◽  
Porous Texture ◽  
129Xe Nmr ◽  
Line Shapes ◽  
X Ray Scattering

AbstractAddition of surfactants in TEOS derived sols leads to micro- or mesoporous materials whose porous texture can be varied by changing the surfactant quantity and/or chain length. This series of materials, with a relatively narrow pore size distribution, is well adapted to study the potentialities of an innovative characterization technique like 129Xe Nuclear Magnetic Resonance in comparison with Small Angle X-ray Scattering and N2 adsorption. SAXS revealed a high surface rugosity of the materials and a good correlation with pore hydraulic radius distributions measured by N2 adsorption. Using 129Xe NMR, we have studied the Xe chemical shifts (δXe,) as a function of pXe, and have pointed out several original results showing the importance, for microporous materials, of the NMR line shapes and of the slope of the lines δXe.=f(pXe).

Solid state carbon and proton line shapes for the characterization of phenylene group motion in polycarbonates

1983 ◽  
Vol 16 (9) ◽  
pp. 1552-1554 ◽  
Author(s):  
Paul T. Inglefield ◽  
Robert M. Amici ◽  
John F. O'Gara ◽  
Chi Cheng Hung ◽  
Alan Anthony Jones
Keyword(s):  
Solid State ◽  
Line Shapes ◽  
Group Motion ◽  
Phenylene Group

Averaging of products of Lorentzian line shapes over thermal velocities

1968 ◽  
Vol 4 (7) ◽  
pp. 468-469 ◽  
Author(s):  
C. Heer ◽  
R. Settles ◽  
J. Bupp
Keyword(s):  
Lorentzian Line ◽  
Line Shapes

scholarly journals Characterization of Metal/Carbon Multilayers by Raman Spectroscopy

1989 ◽  
Vol 160 ◽  
Author(s):  
David D. Allred ◽  
Qi Wang ◽  
Jesus Gonzalez-Hernandez
Keyword(s):  
Raman Spectroscopy ◽  
Amorphous Semiconductor ◽  
Laser Raman Spectroscopy ◽  
Plasma Confinement ◽  
Ray Optics ◽  
X Ray ◽  
Laser Raman ◽  
Line Shapes ◽  
Two Peaks

AbstractLaser Raman spectroscopy has been found to be useful for characterizing amorphous semiconductor multilayers, especially the interfaces of multilayers. Recently, we have extended this technique to the characterization of magnetron sputtered multilayers commonly used as reflectors in soft x-ray optics. Unlike the multilayers previously studied which contained only semiconductors and dielectrics, these are generally semiconductor/metal multilayers. We report here on the Raman characterization of the most common class of multilayers used in soft x-ray optics, those that contain a high density metal like tungsten interspersed with layers of carbon. In all of the metal/carbon multilayers the dominate feature in the Raman spectra is due to a-C. The a-C spectra consists of a broad peak at about 1560 cm-1 (G-peak) and a shoulder at about 1400 cm-1 (D-peak). This can be deconvoluted with Gaussian line shapes to yield two peaks (one at about 1560 to 1570 cm-1 and the other at about 1380 to 1420 cm-1). Among the W/C multilayer samples peak positions and relative magnitudes changed little with carbon thickness over the range of 1 to 12 nm. Significant differences are, however, seen as the identity of the metal component is altered or, especially, as the preparations are varied. For example, the intensity ratio of the D-peak to G-peak was much larger for multilayer samples prepared under conditions of good plasma confinement.

Broadening and shifting of the Raman Q branch in D2 and D2–He mixtures, II: line shapes, fitting routines, and effects nonlinear in density

1994 ◽  
Vol 72 (11-12) ◽  
pp. 891-896 ◽  
Author(s):  
P. M. Sinclair ◽  
P. Duggan ◽  
J. W. Forsman ◽  
J. R. Drummond ◽  
A. D. May
Keyword(s):  
Molecular Dynamics ◽  
Line Shape ◽  
Preceding Paper ◽  
Binary Collision ◽  
Spectral Profile ◽  
Lorentzian Line ◽  
Line Shapes ◽  
And Shifts ◽  
Three Body ◽  
First Time

In the preceding paper we fitted the experimental profiles using a single Lorentzian line shape and assumed that the width and shift were proportional to the density. Here we discuss nonlinear contributions to widths and shifts and present a different spectral profile and analysis that allows us (i) to determine unbiased, binary collision, impact limit, broadening and shifting coefficients; (ii) to disentangle several effects nonlinear in the density; and, subsequently, (iii) to observe broadening and shifting arising purely from the correlation between perturbers and three-body interactions. This is a new avenue of research in molecular dynamics. In addition, measurements of the broadening of the depolarized part of the Q branch in D2 are reported for the first time.

Characterization of natural gas hydrates by nuclear magnetic resonance and dielectric relaxation

1977 ◽  
Vol 55 (20) ◽  
pp. 3641-3650 ◽  
Author(s):  
D. W. Davidson ◽  
S. K. Garg ◽  
S. R. Gough ◽  
R. E. Hawkins ◽  
J. A. Ripmeester
Keyword(s):  
Guest Molecule ◽  
Continuous Wave ◽  
Type I ◽  
Tetrahedral Symmetry ◽  
Guest Molecules ◽  
Line Shapes ◽  
Dielectric Absorption ◽  
Dielectric Data ◽  
First Time

Continuous-wave proton nmr spectra of the clathrate hydrates and/or deuteriohydrates of methane, ethane, propane, isobutane, and neopentane–D2S have been recorded down to 2 K. Between 50 and 200 K each H2O hydrate spectrum consists of a line 3 to 4 G wide from reorienting guest molecules and a broader band from rigid water molecules. Line shapes characteristic of non-rotating guests are obtained in D2O hydrates at low temperatures, except for methane which gives a narrow line to 2 K. Neopentane, shown for the first time to be capable of enclathration, exhibits a Resing effect and other features related to its tetrahedral symmetry. Low-temperature dielectric absorption from reorienting guest-molecule dipoles has been measured in H2S, propane, isobutane, and n-butane–H2S hydrates. For steric reasons n-butane is encaged as a gauche rather than the trans isomer. Average barriers to reorientation estimated from nmr and dielectric data are 1.2 kcal/mol for ethane in type I hydrate and 0.6, 1.2, 1.4, and 0.8 kcal/mol for propane, isobutane, n-butane, and neopentane in type II.

scholarly journals Detection of thermodynamic “valley noise” in monolayer semiconductors: Access to intrinsic valley relaxation time scales

2019 ◽  
Vol 5 (3) ◽  
pp. eaau4899 ◽  
Author(s):  
M. Goryca ◽  
N. P. Wilson ◽  
P. Dey ◽  
X. Xu ◽  
S. A. Crooker
Keyword(s):  
Time Scales ◽  
Relaxation Times ◽  
External Perturbation ◽  
Transition Metal Dichalcogenide ◽  
Pump Probe ◽  
Lorentzian Line ◽  
Line Shapes ◽  
Quantitative Measurements ◽  
Two Dimensional Materials ◽  
Valley Polarization

Together with charge and spin, many novel two-dimensional materials also permit information to be encoded in an electron’s valley degree of freedom—that is, in particular momentum states in the material’s Brillouin zone. With a view toward valley-based (opto)electronic technologies, the intrinsic time scales of valley scattering are therefore of fundamental interest. Here, we demonstrate an entirely noise-based approach for exploring valley dynamics in monolayer transition-metal dichalcogenide semiconductors. Exploiting their valley-specific optical selection rules, we use optical Faraday rotation to passively detect the thermodynamic fluctuations of valley polarization in a Fermi sea of resident carriers. This spontaneous “valley noise” reveals narrow Lorentzian line shapes and, therefore, long exponentially-decaying intrinsic valley relaxation. Moreover, the noise signatures validate both the relaxation times and the spectral dependence of conventional (perturbative) pump-probe measurements. These results provide a viable route toward quantitative measurements of intrinsic valley dynamics, free from any external perturbation, pumping, or excitation.

Comparative analysis of electron-phonon relaxation in a semiconducting carbon nanotube and a PbSe quantum dot

2008 ◽  
Vol 80 (7) ◽  
pp. 1433-1448 ◽  
Author(s):  
Bradley F. Habenicht ◽  
Svetlana V. Kilina ◽  
Oleg V. Prezhdo
Keyword(s):  
Carbon Nanotube ◽  
Quantum Dot ◽  
Density Functional ◽  
Low Frequency ◽  
Electronic Energy ◽  
Relaxation Processes ◽  
Phonon Modes ◽  
Lorentzian Line ◽  
Line Shapes ◽  
Optical Modes

The key features of the phonon-induced relaxation of electronic excitations in the (7,0) zig-zag carbon nanotube (CNT) and the Pb16Se16 quantum dot (QD) are contrasted using a time-domain ab initio density functional theory (DFT) simulation. Upon excitation from the valence to the conduction band (CB), the electrons and holes nonradiatively decay to the band-edge in both materials. The paper compares the electronic structure, optical spectra, important phonon modes, and decay channels in the CNT and QD. The relaxation is faster in the CNT than in the QD. In the PbSe QD, the electronic energy decays by coupling to low-frequency acoustic modes. The decay is nonexponential, in agreement with non-Lorentzian line-shapes observed in optical experiments. In contrast to the QD, the excitation decay in the CNT occurs primarily via high-frequency optical modes. Even though the holes have a higher density of states (DOS), they relax more slowly than the electrons, due to better coupling to low-frequency vibrations. Further, the expected phonon bottleneck is not observed in the QD, as rationalized by a high density of optically dark states. The same argument applies to the CNT. The computed results agree well with experimentally measured ultrafast relaxation time-scales and provide a unique atomistic picture of the electron-phonon relaxation processes.

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