Infrared Spectra Simulation

Infrared spectra are strongly dependent on the 3D structure of a compound, as reflected by the success of attempts to simulate infrared spectra from 3D structure representations (see Section 10.2.5). Infrared spectra should therefore be taken as representations of a chemical compound for modeling properties that are suspected to be dependent on the 3D structure of a compound NMR spectra also depend on... 

Extensive studies about the behaviour of the learning machine have been performed with simulated infrared spectra C2333-... 

Figure 7 Comparison of observed to simulated infrared spectra in the u(CO) region for (la )-(ld ) as a function of the intramolecular electron transfer rate constant, k. ...

Figure 14 Simulated infrared spectra for LVD 10a (a), dimer 10c (b), trimer lOf (c) and tetramer lOg (d) with parameters 50% Gaussian + 50% Lorentzian functions, 20 cm" peak width frequencies and relative intensities based on QC calculations of B3PW91/6-31G(d) with a scaUng factor of 0.949. Reproduced from [38] with permission of Amer. Chem. Soc.

On the basis of B3LYP/6-311++G(d,p) calculations, infrared spectra are simulated for nonplanar EC conformation. The non-planar EC with Q symmetry has 24 fundamental vibrational modes, half of which belong to the respective irreducible representations A and B of the point group C. Eigure 5 shows the simulated infrared spectra for the isolated molecule and that in solvent, together with experimental data. Solvent effect results in the red shift of the stretching vibration for C=0 1858 vs. 1761 cm ). The relative... 

F. Wang, F.R.W. McCouit, R.J. Le Roy, Use of simulated infrared spectra to test N2-Ar pair potentials and dipole moment surfaces. Molec. Phys. 88(3), 821-840 (19%)... 

To perform a vibrational analysis, choose Vibrationson the Compute menu to invoke a vibrational analysis calculation, and then choose Vibrational Dectrum to visualize the results. The Vibrational Spectrum dialog box displays all vibrational frequencies and a simulated infrared spectrum. You can zoom and pan in the spectrum and pick normal modes for display, using vectors (using the Rendering dialog box from Display/Rendering menu item) and/or an im ation. 

Fig. 7.12 Experimental and calculated infrared spectra for liquid water. The black dots are the experimental values. The thick curve is the classical profile produced by the molecular dynamics simulation. The thin curve is obtained by applying quantum corrections. (Figure redrawn from Guilbt B 1991. A Molecular Dynamics Study of the Infrared Spectrum of Water. Journal of Chemical Physics 95 1543-1551.)...

A simulation of the far infrared spectrum of liquid water and steam at temperatures from 273 to 473 K was undertaken, based on molecular dynamics techniques [122]. 

D. Levesque, J. J. Weis, Ph. Marteau, J. Obriot, and F. Fondere. Collision induced far infrared spectrum of liquid N2 Computer simulations and experiment. Molec. Phys., 54 1161, 1985. 

The infrared spectrum of the iron oxide (Figure 19) used to simulate ocher displays distinctive absorbance bands in the region of 537 cm-1 and 465 cm-1. Not only are the bands obvious in fibers pigmented with iron oxide, but the rabbit hair which had been colored with the pigment retained evidence of that pigmentation even when it was charred (Figure 20). 

The spectral dependence of the light sensitivity (as indicated by yellowing) of free films of Parylene-C was determined. A Heraeus Sun-Test chamber, equipped with a xenon arc lamp filtered to yield a simulated solar spectrum, was used for the irradiation. An additional infrared filter minimized sample heating. The irradiance at the sample location was originally 0.83 W/m2 at 340 nm, but the output decreased approximately 20% after 1500 hours use. Long band-pass optical filters with nominal cut-offs of 305 nm, 345 nm, 385 nm and 400 nm were inserted between the xenon lamp and the Parylene-C film samples to determine the wavelength threshold for yellowing. The sample temperature was maintained at 30+ 2 °C with a water-cooled... 

The analysis of the dynamics and dielectric relaxation is made by means of the collective dipole time-correlation function (t) = (M(/).M(0)> /( M(0) 2), from which one can obtain the far-infrared spectrum by a Fourier-Laplace transformation and the main dielectric relaxation time by fitting < >(/) by exponential or multi-exponentials in the long-time rotational-diffusion regime. Results for (t) and the corresponding frequency-dependent absorption coefficient, A" = ilf < >(/) cos (cot)dt are shown in Figure 16-6 for several simulated states. The main spectra capture essentially the microwave region whereas the insert shows the far-infrared spectral region. 

Fig. 7. Infrared spectrum of liquid water from CP-MD simulation top) and from experiment bottom,)...

The simulation of infrared spectra with CPG networks has already been described. The more interesting topic lies at hand The input of a query infrared spectrum into a reverse-trained Kohonen network provides a structure descriptor. The question now is whether it is possible to obtain a 3D structure from this descriptor. 

Pd, and Pt PP2 is PhP(CH2CH2PPh2)2 and R is C2H5 or OCH ) are all new complexes and have been characterized by P and H NMR spectroscopy, infrared spectroscopy, and elemental analysis in addition to the electrochemical studies described above. The P NMR spectrum of [Pd(PP2)P(0Me) ](BF )2 is shown in Figure 1 along with the simulated NMR spectrum. All of the spectral and analytical data are consistent with the formulation of this complex and the other complexes in Table II as square-planar metal complexes. 

A preliminary ab initio molecular dynamics simulation has been carried using the Car-Parrinello approach [9]. The volume of the simulation cell was kept constant at the experimental value of the moganite type PON. The cell contained 72 atoms ( P24O24N24 ) The weighted density of states of PON obtained from the ab intio molecular dynamics simulation is compared with the infrared spectrum in Fig. 4. It can be seen that the gross features of the experimental spectrum are reasonably reproduced in the simulation. 

Fig. 16. (a) Extra-framework cation sites in X- and Y-type zeolites, (b) Far- infrared spectrum of Na-Y with band assignments to cation sites according to [232]. (c) Experimental IR spectrum in comparison to simulated spectra calculated according to the shell model and occupancy of different cation sites, (d) Experimental spectrum in comparison to power spectra simulated by MD at occupancy of different cation sites (parts c and d from [79] with permission)... 

Fig. 24 Difference infrared spectrum, obtained by subtraction of the spectrum recorded after the matrix deposition (negative bands) from the spectrum recorded after UV (A = 290 nm 78 min) irradiation (positive bands) of matrix-isolated saccharin (a), compared with the theoretical one obtained by subtraction of the simulated spectrum of saccharin from iso-saccharin Reprinted with permission from L. Duarte, 1. Reva, M. L. S. Cristiano and R. Fausto, J. Org. Chem., 2013, 78, 3271. Copyright (2013) American Chemical Society.

Molecular dynamics attempts to solve the dynamically evolving ensemble of molecules given the interactions between molecules. The form of the forces between molecules or atoms, the number of interactions (i.e., two- or three-body interactions), and the number of molecules that can be tackled by the program determine the success of the model. Molecular dynamics simulations can predict the internal energy, heat capacity, viscosity, and infrared spectrum of the studied compound and form an integral part in the determination and refinement of structures from X-ray crystallography or nuclear magnetic resonance (NMR) experiments. 

Fig. 5.9. Simulation of the infrared spectrum of the ethyl radical at two different temperatures and two different resolutions. Two advantages of low rotational temperature are evident a less congested spectrum and more population per low energy state.

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