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