THEORETICAL VIBRATIONAL-SPECTRA OF NEUTRAL AND DOPED POLY(P-PHENYLENESULFIDE) OLIGOMERS

The vibrational properties of the first oligomers of poly(p-phenylene sulfide) (PPS) in their neutral, singly and doubly ionized states have been computed at the ab-initio SCF level followed by scaling of the a b-initio force constants with appropriate scale factors. The effect of the basis set on geometries and vibrational spectra has been studied, and the results have been compared with the available experimental da ta relative to the oligomers,and to the polymer. The 3-21G basis set has been found to be a satisfactory compromise between accuracy and co mputional effort. In the trimer, the smallest oligomer whose spectra c ontain all the essential features pertinent to the polymer, ionization has been found to give rise to a strong intensity enhancement of a sm all number of selected vibrational bands in the infrared and in the Ra man spectra, in good agreement with the experimental findings. Combini ng the experimental and theoretical Raman spectra of the doped trimer with the experimental and theoretical electronic spectra of the same s ystem suggests that dications-in addition to radical cations-are forme d upon doping.