Condensed Aromatics. Part III. In-Plane Molecular Vibrations of Pyrene

Abstract

A new force field is developed for the in-plane vibrations of condensed aromatics using pyrene as a test molecule. Only five parameters are employed in this force field, which improves a four- parameter approximation previously investigated. Still the simple five-parameter approximation gives calculated vibrational frequencies in good agreement with those from the more elaborate Califano-Neto force field.In the course of the normal coordinate analysis the Hüekel molecular orbitals have been de­duced. The CC stretching parameters were modified by means of the calculated bond orders. A complete set of independent symmetry coordinates (both in-plane and out-of-plane) for the pyrene molecular model was developed.New experimental data from infrared and Raman spectra for pyrene are reported.Also the mean amplitudes of vibration are studied in detail. It is concluded that the simple five-parameter approximation gives reliable mean amplitudes, which undoubtedly are accurate enough for the interpretation of gas electron diffraction data.Finally the calculated frequencies and mean amplitudes of benzene are given. The mean amplitudes are again found to be very accurate in spite of some substantial inaccuracies in the frequencies.

Condensed Aromatics. Part V

“…Table 6 shows the different ranges obtained for the inner and outer distance of the shortest type (involving two bonds). The ranges of interatomic distances (r) emerged from the experimental structure parameters actually used in the normal coordinate analyses [2,4]. The results illustrate the important influence of environments on the mean amplitudes, which has made the distinction between inner and outer distances necessary.…”

“…A simple, new aromatic force field for the in-plane vibrations of condensed aromatics was described in previous parts of this series [1,2] and referred to as five-parameter approximation. This force field was found to be useful in particular for computing reliable mean amplitudes of vibration [3].…”

“…This force field was found to be useful in particular for computing reliable mean amplitudes of vibration [3]. Such quantities were computed for benzene and pyrene [2] along with naphthalene, anthracene and coronene [4J.…”

“…The calculated in-plane vibrational frequencies and mean amplitudes of vibration are reported. Furthermore, a systematization of the mean amplitudes for nonbonded CC distances is carried out, based on the computations for benzene [2], naphthalene [4], anthracene [4], pyrene [2], coronene [4] and naphthacene (present work).…”

Lattice-dynamical evaluation of temperature factors for aromatic hydrocarbons, including internal molecular motion: a straightforward systematic procedure

“…A good review of this is given especially in books by Cyvin (1968Cyvin ( , 1972; Cyvin himself is co-author of several papers dealing with this subject (e.g. Whitmer, Cyvin & Cyvin, 1978;Bakke, Cyvin, Whitmer, Cyvin, Gustavsen & Klaeboe, 1979;Cyvin, Cyvin, Brunvoll, Whitmer, Klaeboe & Gustavsen, 1979). Application of these spectroscopic routines in crystals, especially concerning the FG method, was considered by Scheringer and his group (Scheringer & Fadini, 1979;Ishii & Scheringer, 1979).…”