scholarly journals Theoretical model of infrared spectra of hydrogen bonds in molecular crystals of 2-thiopheneacetic acid: Fermi resonance and Davdov coupling effects.

2016 ◽  
Vol 35 (2) ◽  
pp. 157
Author(s):  
Noureddine Issaoui ◽  
Hafedh Abdelmoulahi ◽  
Henryk T. Flakus ◽  
Houcine Ghalla ◽  
Brahim Oujia
Keyword(s):  
Line Shape ◽  
Low Frequency ◽  
Fermi Resonance ◽  
Transmission Method ◽  
Line Shapes ◽  
Breaking Mechanism ◽  
Rule Breaking ◽  
Indirect Damping ◽  
Low Frequency Mode ◽  
Insight Into

<p>A quantum theoretical approach, within the adiabatic approximation and taking into account a strong non-adiabatic correction via the resonant exchange between the fast mode excited states of the two moieties of the dimer. The intrinsic anharmonicity of the low-frequency mode through a Morse potential, direct and indirect damping, and a selection rule breaking mechanism for forbidden transitions, is applied to reproduce the υ<sub>X-H </sub>IR line shape of cyclic dimers of moderately H-bonded species in the crystalline phase. The results are used to gain an insight into the experimental spectral line shapes obtained by the transmission method. This approach fits satisfactorily the experimental line shape of 2-thiopheneacetic acid and predicts their evolution with isotopic substitution. Numerical calculations show that mixing of all these effects allows one to reproduce the main features of the experimental IR line shapes. </p>

H NMR Evidence for a Change in The Local Hydrogen Environment of Sites Associated with the Staebler-Wronski Effect in a-Si:H

2002 ◽  
Vol 715 ◽  
Author(s):  
T. Su ◽  
Robin Plachy ◽  
P. C. Taylor ◽  
S. Stone ◽  
G. Ganguly ◽  
...  
Keyword(s):  
Line Shape ◽  
Defect Density ◽  
Hydrogen Atoms ◽  
Hydrogen Environment ◽  
H Nmr ◽  
Line Shapes ◽  
Different Temperatures ◽  
Staebler Wronski Effect

AbstractWe study the H NMR line shapes of a sample of a-Si:H under several conditions: 1) as grown, 2) light-soaked for 600 hours, and 3) light-soaked followed by annealing at different temperatures. At T = 7 K, the NMR line shape of the sample after light soaking exhibits an additional doublet compared to that of the sample as-grown. This doublet is an indication of a closely separated hydrogen pair. The distance between the two hydrogen atoms is estimated to be about (2.3 ± 0.2) Å. The concentration of these hydrogen sites is estimated to be between 1017 and 1018 cm-3 consistent with ESR measurements of the defect density after light soaking. This doublet disappears after the sample is annealed at 200°C for 4 hours.

Quantum Mechanical Interpretation of the Ultra-Low Energy Methyl-Rotation Dynamics in Porous Metal-Organic Frameworks Probed by Low-Frequency Vibrational Spectroscopy and ab initio Simulations

2018 ◽  
Author(s):  
Qi Li ◽  
Adam J. Zaczek ◽  
Timothy M. Korter ◽  
J. Axel Zeitler ◽  
Michael T. Ruggiero
Keyword(s):  
Ab Initio ◽  
Metal Organic Frameworks ◽  
Low Frequency ◽  
Rotor Dynamics ◽  
Quantum Mechanical ◽  
Valuable Insight ◽  
Void Space ◽  
Ab Initio Simulations ◽  
Metal Organic ◽  
Insight Into

<div>Understanding the nature of the interatomic interactions present within the pores of metal-organic frameworks</div><div>is critical in order to design and utilize advanced materials</div><div>with desirable applications. In ZIF-8 and its cobalt analogue</div><div>ZIF-67, the imidazolate methyl-groups, which point directly</div><div>into the void space, have been shown to freely rotate - even</div><div>down to cryogenic temperatures. Using a combination of ex-</div><div>perimental terahertz time-domain spectroscopy, low-frequency</div><div>Raman spectroscopy, and state-of-the-art ab initio simulations,</div><div>the methyl-rotor dynamics in ZIF-8 and ZIF-67 are fully charac-</div><div>terized within the context of a quantum-mechanical hindered-</div><div>rotor model. The results lend insight into the fundamental</div><div>origins of the experimentally observed methyl-rotor dynamics,</div><div>and provide valuable insight into the nature of the weak inter-</div><div>actions present within this important class of materials.</div>

Critical Raman line shape behavior of fluid nitrogen

2004 ◽  
Vol 76 (1) ◽  
pp. 147-155 ◽  
Author(s):  
M. Musso ◽  
F. Matthai ◽  
D. Keutel ◽  
K.-L. Oehme
Keyword(s):  
Raman Line ◽  
Line Shape ◽  
Line Broadening ◽  
Vibrational Resonance ◽  
Critical Isochore ◽  
Molecular Fluids ◽  
Detection Techniques ◽  
Gas Phases ◽  
Line Shapes ◽  
Band Position

Isotropic Raman line shapes of simple molecular fluids exhibit critical line broadening near their respective liquid-gas critical points. In order to observe this phenomenon, it is essential that the band position of a given vibrational mode is density-dependent, and that vibrational depopulation processes negligibly contribute to line broadening. Special attention was given to the fact that the isotropic (i.e., nonrotationally broadened) line shape of liquid N2 is affected by resonant intermolecular vibrational interactions between identical oscillators. By means of the well-chosen isotopic mixture (14N2).975 - (14N15N).025, the temperature and density dependences of shift, width, and asymmetry of the resonantly coupled 14N2 and, depending on the S/N ratio available, of the resonantly uncoupled 14N15N were determined, with up to milli-Kelvin resolution, in the coexisting liquid and gas phases and along the critical isochore, using a highest-resolution double monochromator and modern charge-coupled device detection techniques. Clear evidence was found that vibrational resonance couplings are present in all dense phases studied.

scholarly journals Pressure effects on water vapour lines: beyond the Voigt profile

2012 ◽  
Vol 370 (1968) ◽  
pp. 2495-2508 ◽  
Author(s):  
N. H. Ngo ◽  
H. Tran ◽  
R. R. Gamache ◽  
J. M. Hartmann
Keyword(s):  
Water Vapour ◽  
Line Shape ◽  
Pressure Effects ◽  
Shape Model ◽  
Line Shapes ◽  
Voigt Profile ◽  
Voigt Model ◽  
Velocity Changes ◽  
Dynamics Simulations ◽  
Induced Velocity

A short overview of recent results on the effects of pressure (collisions) regarding the shape of isolated infrared lines of water vapour is presented. The first part of this study considers the basic collisional quantities, which are the pressure-broadening and -shifting coefficients, central parameters of the Lorentzian (and Voigt) profile and thus of any sophisticated line-shape model. Through comparisons of measured values with semi-classical calculations, the influences of the molecular states (both rotational and vibrational) involved and of the temperature are analysed. This shows the relatively unusual behaviour of H 2 O broadening, with evidence of a significant vibrational dependence and the fact that the broadening coefficient (in cm −1 atm −1 ) of some lines increases with temperature. In the second part of this study, line shapes beyond the Voigt model are considered, thus now taking ‘velocity effects’ into account. These include both the influence of collisionally induced velocity changes that lead to the so-called Dicke narrowing and the influence of the dependence of collisional parameters on the speed of the radiating molecule. Experimental evidence of deviations from the Voigt shape is presented and analysed. The interest of classical molecular dynamics simulations, to model velocity changes, together with semi-classical calculations of the speed-dependent collisional parameters for line-shape predictions from ‘first principles’, are discussed.

13C NMR-spektroskopische Untersuchungen an Äthylaluminiumverbindungen / 13C NMR Spectroscopic Investigations of Ethylaluminium Compounds

1976 ◽  
Vol 31 (6) ◽  
pp. 730-736 ◽  
Author(s):  
R. Rottler ◽  
C. G. Kreiter ◽  
G. Fink
Keyword(s):  
Temperature Dependence ◽  
Exchange Reaction ◽  
13C Nmr ◽  
Line Shape ◽  
Nmr Spectra ◽  
Exchange Process ◽  
Kcal Mole ◽  
Line Shapes ◽  
Calculated Line ◽  
C Nmr

The 13C NMR spectra of the ethylaluminium compounds [Al(C2H5)xCl3_x]2 x = 1, 1,5, 2 and 3 are presented and factors governing the temperature dependence of the line shape are discussed. The exchange reaction of terminal ethyl groups for chlorine ligands and ethyl ligands, resp., in ethylaluminium-sesquichloride was investigated by fitting the calculated line shapes to the observed spectra.The energy of activation of this exchange process was determined as to be 12,3 ‡ 1,5 kcal/mole. The synthesis of 13C2-[Al(C2H5)Cl2]2 is described.

scholarly journals Collisional line shapes for low frequency vibrations of adsorbates on a metal surface

2004 ◽  
Vol 121 (17) ◽  
pp. 8580 ◽  
Author(s):  
J. L. Vega ◽  
R. Guantes ◽  
S. Miret-Artés ◽  
D. A. Micha
Keyword(s):  
Metal Surface ◽  
Low Frequency ◽  
Line Shapes

A computational insight into the relationship between side chain IR line shapes and local environment in fibril-like structures

2021 ◽  
Vol 154 (8) ◽  
pp. 084105
Author(s):  
Sandra M. V. Pinto ◽  
Nicola Tasinato ◽  
Vincenzo Barone ◽  
Laura Zanetti-Polzi ◽  
Isabella Daidone
Keyword(s):  
Local Environment ◽  
Side Chain ◽  
Line Shapes ◽  
The Relationship ◽  
Insight Into

Oscillations in a Collapsed-Tube Analog of the Brachial Artery Under a Sphygmomanometer Cuff

1989 ◽  
Vol 111 (3) ◽  
pp. 185-191 ◽  
Author(s):  
C. D. Bertram ◽  
C. J. Raymond ◽  
K. S. A. Butcher
Keyword(s):  
High Frequency ◽  
Flow Characteristics ◽  
Low Frequency ◽  
Collapsible Tube ◽  
Tube Size ◽  
Low Frequency Oscillations ◽  
Central Segment ◽  
Experimental Parameters ◽  
Aqueous Flow ◽  
Low Frequency Mode

To determine whether self-excited oscillations in a Starling resistor are relevant to physiological situations, a collapsible tube conveying an aqueous flow was externally pressurized along only a central segment of its unsupported length. This was achieved by passing the tube through a shorter and wider collapsible sleeve which was mounted in Starling resistor fashion in a pressure chamber. The tube size and material, and all other experimental parameters, were as used in our previous Starling resistor studies. Both low- and high-frequency self-excited oscillations were observed, but the low-frequency oscillations were sensitive to the sleeve type and length relative to unsupported distance. Pressure-flow characteristics showed multiple oscillatory modes, which differed quantitatively from those observed in comparable Starling resistors. Slow variation of driving pressure gave differing behavior according to whether the pressure was rising or falling, in accord with the hysteresis noted on the characteristics and in the tube law. The results are discussed in terms of the various possible mechanisms of collapsible tube instability, and reasons are presented for the absence of the low-frequency mode under most physiological circumstances.

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