1,449 research outputs found
Translational and Librational Lattice Frequencies in 6-N,N-Diacetylaminochrysene and 2,4-Dinitrobenzoic Acid Crystals
The root-mean-square libration amplitude derived from non-rigid-body thermal motion analysis of 6-N,N-diacetylaminochryseneand 2,4-dinitrobenzoic acid predicts torsional frequencies in satisfactory agreement with the Raman spectra. Translational and librational lattice frequencies of the whole molecules derived from the L and T components are generally consistent with the spectroscopic results
Analysis of the H-bridge in Carboxyllic Acids in Terms of Stabilization Energy Derived from Bond Lengths. Non-Hammett Properties of p-Substituted Benzoic Acids in the Crystalline State
Harmonic oscillator stabilization energy (HOSE) is defined as
the negative value of deformation energy necessary to transform
a molecule from its natural geometry to its Kekule structure with
purely single and double bonds. It was found that HOSE-values for
dimers of carboxylic acids with centrosymmetric hydrogen bonds
are well related (correlation coeff. r = 0.972) to the Ro . . . o distances
for 19 species for which measurements were carried out in both
the crystalline and gaseous states. Stability of many other Jt-
systems, e. g. aromatic and unsaturated hydrocarbons, polymethine
systems (e.g. cyanine dyes), EDA-complexes, quinoid systems, etc.
are successfully described in terms of HOSE-values
Vibrational Recognition of Adsorption Sites for Carbon Monoxide on Platinum and Platinum-Ruthenium Surfaces
We have studied the vibrational properties of CO adsorbed on platinum and
platinum-ruthenium surfaces using density-functional perturbation theory within
the Perdew-Burke-Ernzerhof generalized-gradient approximation. The calculated
C-O stretching frequencies are found to be in excellent agreement with
spectroscopic measurements. The frequency shifts that take place when the
surface is covered with ruthenium monolayers are also correctly predicted. This
agreement for both shifts and absolute vibrational frequencies is made more
remarkable by the frequent failure of local and semilocal exchange-correlation
functionals in predicting the stability of the different adsorption sites for
CO on transition metal surfaces. We have investigated the chemical origin of
the C-O frequency shifts introducing an orbital-resolved analysis of the force
and frequency density of states, and assessed the effect of donation and
backdonation on the CO vibrational frequency using a GGA + molecular U
approach. These findings rationalize and establish the accuracy of
density-functional calculations in predicting absolute vibrational frequencies,
notwithstanding the failure in determining relative adsorption energies, in the
strong chemisorption regime.Comment: 21 pages, 9 figure
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