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 ab-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 data relative to the oligomers,and to the polymer. The 3-21G* basis set has been found to be a satisfactory compromise between accuracy and computional effort. In the trimer, the smallest oligomer whose spectra contain all the essential features pertinent to the polymer, ionization has been found to give rise to a strong intensity enhancement of a small number of selected vibrational bands in the infrared and in the Raman spectra, in good agreement with the experimental findings. Combining the experimental and theoretical Raman spectra of the doped trimer with the experimental and theoretical electronic spectra of the same system suggests that dications-in addition to radical cations-are formed upon doping.