Molecular Vibration Coupling Research Articles

Reduzierte Zustandssummenverhältnisse isotoper Moleküle auf quantenchemischer Grundlage: II. Mitt. MND0- und MIND0/3-MO-Berechnungen zur H/D-Substitution

The reduced partition function ratios of 34 compounds concerning the H/D-substitution are mutually compared by means of pictures of their temperature dependence. At this general relationships between those ratios and the chemical structure of the corresponding molecules are evident. These are mainly based on the structural dependence of both the force constants and the coupling of molecular vibrations. The existence of certain characteristic values of reduced partition function ratios for several groups (CH3, CH2, CH OH) is obvious.

Electron–Molecular Vibration Coupling in Trimerized Organic Ion‐Radical Semiconductors

AbstractThe totally‐symmetric (ag) internal molecular vibrational excitations in a trimer are considered. The mode corresponding to the charge transfer (CT) between non‐centric molecules is shown to be responsible for the indirect IR activity. The trimer MO calculations in the site occupation representation are simplified and the symmetry of the basis states is taken into account. Eigenstates and eigenvalues of the molecular trimer with two radical electrons are calculated as a function of the transfer integral, t, and the Coulomb „on‐site”︁ repulsion, U. The following interpretation of the absorption spectrum of the cesium salt of tetracyanoquinodimethane Cs2(TCNQ)3 is given: the 1.4 eV peak is attributed to intratrimer charge transfer excitation, the less than 0.6 eV peak corresponds to the electronic transition between neighbouring trimers. The electron–molecular vibration coupling constants and Hubbard parameters U and t are evaluated for Cs2(TCNQ)3.

On vibrational population relaxation in solution

A model is presented for the vibrational population relaxation of a polyatomic molecule in solution. The coupling of molecular vibrations leads to a cascade of energy through a sequence of vibrational levels. At each step of the energy redistribution energy can be transferred to nonvibrational (solvent) degrees of freedom. The model is developed in detail for a two step cascade, incorporating variable coupling potentials between zero order vibrational and solvent eigenstates. The results of these calculations are discussed in the context of time resolved picosecond laser studies of vibrational relaxation in liquids.

Molekulare Schwingungsexzitonen in Fliissigkeiten

The intermolecular coupling of molecular vibrations in molecular crystals is usually treated by the exciton concept. This is identical with the assumption that a potential, which describes the interaction of a vibrating molecule with its neighbours, perturbs the isolated molecule energies and thereby couples the motions of molecules. In most cases this potential will be the transition-dipoletransition- dipole interaction. If one assumes validity of the pair interaction approximation this concept should be able to describe the effects in the liquid state, too. The aim of these considerations is to show, how collective excitation can influence the shape of vibrational bands. Because dipoledipole interaction is strongly orientation dependent, molecular reorientations perturb the coupling of the vibrations and cause motional narrowing. The behaviour of the shapes of the vibration bands of CH3J is discussed on the basis of these considerations. One finds that the band shape of ν2 is mainly broadened by vibration coupling. As expected a distinct motional narrowing is observed, if one increases the temperature from the melting point to the boiling point.