Infrared and Raman activity of polyenes in pristine and doped state.

Abstract

The activity of a normal mode in vibrational spectra of polyenes (short, long or infinite) can be essentially represented by the quantity delta-PHI/deltaR- *(L(R-,i)). PHI is the molecular dipole moment ((mu)) in IR and the molecular polarizability ((alpha)) in Raman respectively. R- is the "effective conjugation coordinate" and L(R-,i) is the content of in the i-th mode. Delta ((mu))/deltaR-vanishes in pristine compounds and is large in doped and photoexcited ones; delta((alpha))/delta(R-) is large for udoped chains and practically vanishing for doped ones. This statement originates from the interpretation of vibrational spectra but is also supported by results of abinitio calculations made by Villars, Dupuis and Clementi