Theory of profiles of hydrogen stretching infrared bands of hydrogen-bonded solids. Multi-Fermi resonance effects and strong coupling between the high-frequency hydrogen stretching vibration and low-frequency phonons

2000 ◽  
Vol 500 (1-3) ◽  
pp. 413-419 ◽  
Author(s):  
H. Ratajczak ◽  
A.M. Yaremko
Keyword(s):  
Strong Coupling ◽  
High Frequency ◽  
Low Frequency ◽  
Fermi Resonance ◽  
Resonance Effects ◽  
Stretching Vibration ◽  
Hydrogen Bonded

scholarly journals Theoretical Studies of Dynamic Interactions in Excited States of Hydrogen-Bonded Systems

2012 ◽  
Vol 2012 ◽  
pp. 1-17 ◽  
Author(s):  
Marek J. Wójcik ◽  
Marek Boczar ◽  
Łukasz Boda
Keyword(s):  
Hydrogen Bonds ◽  
Potential Energy ◽  
Benzoic Acid ◽  
Excited States ◽  
Potential Energy Surfaces ◽  
Low Frequency ◽  
Fermi Resonance ◽  
Tunneling Splittings ◽  
Energy Surfaces ◽  
Hydrogen Bonded

Theoretical model for vibrational interactions in the hydrogen-bonded benzoic acid dimer is presented. The model takes into account anharmonic-type couplings between the high-frequency O–H and the low-frequency O⋯O stretching vibrations in two hydrogen bonds, resonance interactions between two hydrogen bonds in the dimer, and Fermi resonance between the O–H stretching fundamental and the first overtone of the O–H in-plane bending vibrations. The model is used for theoretical simulation of the O–H stretching IR absorption bands of benzoic acid dimers in the gas phase in the first excited singlet state. Ab initio CIS and CIS(D)/CIS/6-311++G(d,p) calculations have been carried out in the à state of tropolone. The grids of potential energy surfaces along the coordinates of the tunneling vibration and the low-frequency coupled vibration have been calculated. Two-dimensional model potentials have been fitted to the calculated potential energy surfaces. The tunneling splittings for vibrationally excited states have been calculated and compared with the available experimental data. The model potential energy surfaces give good estimation of the tunneling splittings in the vibrationally ground and excited states of tropolone, and explain monotonic decrease in tunneling splittings with the excitation of low-frequency out-of-plane modes and increase of the tunneling splittings with the excitation of low-frequency planar modes.

Theoretical Modeling of the N-H and N-D Stretching Bands of Hydrogen-Bonded 1-Methylthymine Crystal and Its Deuterated Form

2006 ◽  
Vol 2 (4) ◽  
pp. 205-219
Author(s):  
Marek Boczar ◽  
Łukasz Boda ◽  
Marek J. Wójcik
Keyword(s):  
Hydrogen Bonds ◽  
High Frequency ◽  
Molecular Crystals ◽  
Low Frequency ◽  
Unit Cell ◽  
Fermi Resonance ◽  
Bending Vibrations ◽  
Theoretical Simulation ◽  
Stretching Vibrations ◽  
Centrosymmetric Dimers

Theoretical model for vibrational interactions in the hydrogen bonds in molecular crystals with four molecules forming two centrosymmetric dimers in the unit cell is presented. The model takes into account anharmonic-type couplings between the high-frequency N-H(D) and the low-frequency N•••O stretching vibrations in each hydrogen bond, resonance interactions (Davydov coupling) between equivalent hydrogen bonds in each dimer, resonance interdimer interactions within an unit cell and Fermi resonance between the N-H(D) stretching fundamental and the first overtone of the N-H(D) in-plane bending vibrations. The vibrational Hamiltonian, selection rules, and expressions for the integral properties of an absorption spectrum are derived. The model is used for theoretical simulation of the νs stretching bands of 1-methylthymine and its ND derivative at 300 K. The effect of deuteration is successfully reproduced by our model.

Infrared Study of Alkyl Isothiocyanates in Carbon Tetrachloride and/or Chloroform Solutions

1993 ◽  
Vol 47 (6) ◽  
pp. 677-686 ◽  
Author(s):  
R. A. Nyquist ◽  
C. W. Puehl
Keyword(s):  
Carbon Tetrachloride ◽  
Alkyl Group ◽  
High Frequency ◽  
Fermi Resonance ◽  
Methyl Ethyl ◽  
Infrared Study ◽  
Tert Butyl ◽  
Electron Donation ◽  
Hydrogen Bonded

The νasym.NCS frequencies for alkyl isothiocyanates occur at higher frequency in CHCl3 or CDCl3 solution than in CCl4 solution. The νasym.NCS mode increases in frequency as the mole % CHCl3/CCl4 increases. The νasym.NCS mode for butyl isothiocyanate occurs at an exceptionally high frequency, and this result is explained in terms of the formation of a pseudo-six-membered intramolecularly hydrogen-bonded ring. The νasym.NCS modes for the alkyl isothiocyanates are corrected for Fermi resonance (FR), with the exception of the propyl analog. The propyl analog appears to have three other modes in FR with νasym.NCS, and an equation has not yet been developed to correct for FR in this case. The unperturbed νasym.NCS frequencies for alkyl isothiocyanates decrease in the alkyl order: methyl, butyl, ethyl, and tert-butyl. The decrease in frequency of νasym.NCS in the order methyl, ethyl, and tert-butyl isothiocyanate is attributed to weakening of the N=C=S bonds due to σ electron donation of each alkyl group. In the case of the butyl analog, the σ electron donation is partially compensated for by the postulated existence of a pseudo-six-membered hydrogen-bonded ring.

Fermi Resonance of Infrared Vibrations in the —NH2 Groups of Polynucleotides

1971 ◽  
Vol 49 (23) ◽  
pp. 3795-3798 ◽  
Author(s):  
G. Zundel ◽  
W. D. Lubos ◽  
K. Kölkenbeck
Keyword(s):  
Hydrogen Bonds ◽  
Harmonic Vibration ◽  
Fermi Resonance ◽  
Bending Vibration ◽  
Doublet Structure ◽  
Stretching Vibration ◽  
Stretching Vibrations ◽  
Band Pair ◽  
Hydrogen Bonded

The —NH2 group causes an intensive band pair in the i.r. spectra of DNA, r.RNA, poly (A + U), and poly (G + C). One band occurs at 3330, another at 3180 cm−1. This band pair is due to the NH stretching vibration of the hydrogen-bonded NH group as well as to the harmonic vibration of the —NH2 bending vibration, whereby these vibrations are coupled via Fermi resonance. This follows on comparison with papers on amines. The weak shoulder in the 3500–3400 cm−1 range is to be assigned to the stretching vibrations of the non hydrogen-bonded NH groups. The doublet structure disappears to a large extent in the denaturated DNA, since the strength of the Fermi resonance depends on the strength of the hydrogen bonds and the hydrogen bonds are of differing strength, due to the bending and stretching. The relative intensities of the two bands are interchanged in the corresponding band pair of the —ND2 groups, for which an explanation can also be given.

Infrared spectra of hydrogen-bonded salicylic acid and its derivatives. Methyl salicylate

1983 ◽  
Vol 61 (7) ◽  
pp. 1449-1452 ◽  
Author(s):  
Marek J. Wójcik ◽  
Czesława Paluszkiewicz
Keyword(s):  
Infrared Spectra ◽  
Methyl Salicylate ◽  
Low Frequency ◽  
Far Infrared ◽  
Gaseous State ◽  
Stretching Vibration ◽  
Intramolecular Hydrogen ◽  
Solid Liquid ◽  
Far Infrared Spectra ◽  
Hydrogen Bonded

Infrared spectra of hydrogen-bonded methyl salicylate have been studied in the temperature range 173–293 K, in solutions of various concentrations (in CCl4) and in the gaseous state. Results show that the molecules form monomerie intramolecular hydrogen bonds in the solid, liquid, and gaseous state. Far-infrared spectra were recorded which give the wavenumber of low-frequency O … O mode used in theoretical reconstruction of the band connected with the O—H stretching vibration. The position and especially the width of this band are determined to a large extent by the influence of the environment.

Simulations of high-resolution images of amorphous silicon films

1986 ◽  
Vol 44 ◽  
pp. 544-545
Author(s):  
G. Y. Fan ◽  
J. M. Cowley
Keyword(s):  
Electron Microscope ◽  
High Frequency ◽  
Fourier Transformation ◽  
Amorphous Materials ◽  
Low Frequency ◽  
Chromatic Aberration ◽  
Structure Information ◽  
Frequency Components ◽  
High Resolution Images ◽  
Spatial Frequency Spectrum

It is well known that the structure information on the specimen is not always faithfully transferred through the electron microscope. Firstly, the spatial frequency spectrum is modulated by the transfer function (TF) at the focal plane. Secondly, the spectrum suffers high frequency cut-off by the aperture (or effectively damping terms such as chromatic aberration). While these do not have essential effect on imaging crystal periodicity as long as the low order Bragg spots are inside the aperture, although the contrast may be reversed, they may change the appearance of images of amorphous materials completely. Because the spectrum of amorphous materials is continuous, modulation of it emphasizes some components while weakening others. Especially the cut-off of high frequency components, which contribute to amorphous image just as strongly as low frequency components can have a fundamental effect. This can be illustrated through computer simulation. Imaging of a whitenoise object with an electron microscope without TF limitation gives Fig. 1a, which is obtained by Fourier transformation of a constant amplitude combined with random phases generated by computer.

SEM image sharpness analysis

1996 ◽  
Vol 54 ◽  
pp. 142-143
Author(s):  
M. T. Postek ◽  
A. E. Vladar
Keyword(s):  
High Frequency ◽  
Low Frequency ◽  
Quantitative Information ◽  
Primary Electron ◽  
Image Sharpness ◽  
Critical Dimensions ◽  
Sem Image ◽  
Frequency Changes ◽  
Electron Microscopes ◽  
Scanning Electron

Fully automated or semi-automated scanning electron microscopes (SEM) are now commonly used in semiconductor production and other forms of manufacturing. The industry requires that an automated instrument must be routinely capable of 5 nm resolution (or better) at 1.0 kV accelerating voltage for the measurement of nominal 0.25-0.35 micrometer semiconductor critical dimensions. Testing and proving that the instrument is performing at this level on a day-by-day basis is an industry need and concern which has been the object of a study at NIST and the fundamentals and results are discussed in this paper.In scanning electron microscopy, two of the most important instrument parameters are the size and shape of the primary electron beam and any image taken in a scanning electron microscope is the result of the sample and electron probe interaction. The low frequency changes in the video signal, collected from the sample, contains information about the larger features and the high frequency changes carry information of finer details. The sharper the image, the larger the number of high frequency components making up that image. Fast Fourier Transform (FFT) analysis of an SEM image can be employed to provide qualitiative and ultimately quantitative information regarding the SEM image quality.

Real Ear Sound Pressure Levels Developed by Three Portable Stereo System Earphones

1992 ◽  
Vol 1 (4) ◽  
pp. 52-55 ◽  
Author(s):  
Gail L. MacLean ◽  
Andrew Stuart ◽  
Robert Stenstrom
Keyword(s):  
High Frequency ◽  
Sound Pressure ◽  
Low Frequency ◽  
Test System ◽  
Output Frequency ◽  
Frequency Effects ◽  
Adult Men ◽  
Frequency Responses ◽  
Significant Difference ◽  
Sound Pressure Levels

Differences in real ear sound pressure levels (SPLs) with three portable stereo system (PSS) earphones (supraaural [Sony Model MDR-44], semiaural [Sony Model MDR-A15L], and insert [Sony Model MDR-E225]) were investigated. Twelve adult men served as subjects. Frequency response, high frequency average (HFA) output, peak output, peak output frequency, and overall RMS output for each PSS earphone were obtained with a probe tube microphone system (Fonix 6500 Hearing Aid Test System). Results indicated a significant difference in mean RMS outputs with nonsignificant differences in mean HFA outputs, peak outputs, and peak output frequencies among PSS earphones. Differences in mean overall RMS outputs were attributed to differences in low-frequency effects that were observed among the frequency responses of the three PSS earphones. It is suggested that one cannot assume equivalent real ear SPLs, with equivalent inputs, among different styles of PSS earphones.

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