M. Gussoni

A simple interpretation of the vibrational spectra of undoped, doped and photoexcited polyacetylene: Amplitude mode theory in the GF formalism

Abstract It is shown that the Amplitude Mode Theory worked out for obtaining a unified interpretation of the vibrational spectra of Polyacetylene can be reformulated in a simpler and more complete way in terms of straightforward concepts of moleculare dynamics.

Infrared intensities: from intensity parameters to an overall understanding of the spectrum

Abstract The current state of the art in the field of vibrational intensity is reviewed. The parametrisation of the infrared intensities and the physical meaning of the parameters is discussed. A comparison is made of experimental infrared atomic charges with those calculated from quantum-chemical methods. The applications of intensity parameters in spectroscopy and in molecular sciences are presented and discussed.

Relaxation contribution to hyperpolarizability. A semiclassical model

Abstract In the presence of strong electromagnetic fields, the response of the material may be non linear. This is usually quantified in terms of the α, β, γ,…tensors. A non-negligible contribution to these tensors originates from the relaxation of nuclei. In this paper a semiclassical treatment is presented which allows to derive an explicit analitic expression for this contribution in terms of vibrational spectroscopic observables.

Atomic charges and charge flows from infrared intensities: C–H bonds

Use is made of experimental infrared absorption intensities for calculating atomic charges and charge flows for a class of simple organic molecules. Various methods are discussed. Correlations of the calculated quantities with other independent structural parameters shed some new light on the peculiarities of the electrical properties of CH bonds.

Infrared intensities: A new tool in chemistry.

Abstract The interpretation of the infrared intensities in terms of atomic polar tensors and of electrooptical parameters allows to derive rich information on the charge distribution in the molecules. Using the results of several studies of this kind, it is now possible to derive information on intramolecular and intermolecular interactions even from “poor” data such as absolute intensities of whole regions in the spectrum or even from relative intensities.

Electronic and relaxation contribution to linear molecular polarizability. An analysis of the experimental values

Abstract This paper reports and comments on the experimental values of \ ga e and \ ga r of more than 650 molecules, where \ ga e and \ ga r are the mean values of the electronic polarizability tensor αe and of the relaxation polarizability tensor αr, respectively. It is assumed that αe and αr sum up to α, the static polarizability of the molecule that can be directly measured through the dielectric constant. Thus, only values of αe independent of the frequency are reported. The principal targets of this paper are: (1) to collect from literature the largest amount of experimental data of \ ga e and \ ga r and try to group the data for classification and characterization of the electrical behaviour of molecules; (2) to find out which classes of molecules have unusual \ ga e and/or \ ga r ; (3) to interpret the data in terms of charge distribution; and (4) to provide a basis for comparing with experiment the values \ ga e and \ ga r calculated by quantum chemical methods. The main conclusions are: \ ga e increases with the number Z of electrons in the molecule so that the polarizability per electron ( \ ga e Z ) is reasonably constant except for conjugated molecules (where it is slightly larger) and for halogenated molecules (where it is much smaller); \ ga r ranges from very low to rather large values, apparently without any correlation nor with the corresponding \ ga e or the number Z of electrons or the number v of oscillators in the molecule; the largest values of \ ga r are reached for molecules having spherical shape and the largest ratio \ ga r \ ga e is attained by molecules containing several halogen atoms. These data seem to suggest an additive scheme for the mean value of the electronic polarizabllity. On the contrary, \ ga r does not obey any additive scheme; large \ ga r and large \ ga r \ ga e seem to be connected to large charge fluxes associated to vibrations and therefore to large electron-phonon coupling. All the above considerations hold for the mean values of the polarizability tensors. A different behaviour of the single components of αe and αr is also discussed.

Charge distribution from infrared intensities: Charges on hydrogen atoms and hydrogen bond

It is known that from infrared intensities it is possible to derive atomic charges and charge fluxes. The intensity parameters of hydrogen atoms which are able to form hydrogen bonds are calculated in this work and compared with those of other hydrogen atoms not showing the same property; they are found to be different. From gas phase infrared intensity measurements one can then determine whether a given hydrogen atom is capable of forming hydrogen bond.

Intramolecular electrical and dynamical interactions in formaldehyde: A discussion based on infrared intensity data

In this paper the infrared intensities of formaldehyde d0 and d2 are interpreted on the basis of electro‐optical parameters. It is shown that infrared intensities can be used as a powerful tool to electro‐optical parameters. It is shown that infrared intensities can be used as a powerful tool to choose among different, even if reasonable, force fields: 16 force fields taken from literature have been examined and only a few of them have been found appropriate to fit infrared intensities. Both electrical and potential intramolecular interactions in CH2O support the hypothesis of a backdonation of electronic charge from the oxygen lone pairs to the CH bonds. An attempt to remove the amibguity in angular electro‐optical parameters has been made on the basis of the ‘‘orbital following approximation.’’

Infrared and Raman intensities of polyethylene and perdeuteropolyethylene by electro‐optical parameters. Single chain

An extension of the electro‐optical theory of valence to the calculation of infrared and Raman intensities of the fundamentals of polymers is presented. The method is applied to the calculation of the infrared and Raman intensities of polyethylene and perdeuteropolyethylene. Parameters from small model molecules have been used. The results are satisfactory, thus providing further evidence that the electro‐optical parameters are transferable. New infrared and Raman spectra of polyethylene and perdeuteropolyethylene have been recorded and are reported. Some implications of intensity calculations in the vibrational assignments of these two polymers are discussed.

Characteristic infrared intensities of CH bonds

Abstract The contribution for CH bond to the total intensity in the CH stretching region (Astr)and to the total intensity in the CH deformation region (Adef) can be easily measured for several compounds. Astr and Adef provide a direct information on the electrical properties of the CH bonds in different surroundings.