The valence electronic structure of isotactic polystyrene revisited

We present a comparison between the experimental UPS spectrum of polystyrene and a theoretically simulated spectrum derived from valence effective Hamiltonian (VEH) calculations. The calculations are carried out on a stereoregular helical isotactic polystyrene chain where the bonds joining the backbone to the phenyl groups are trans relative to the backbone (defining an isotactic polystyrene conformation denoted i-PS). This conformation is different from that considered in a previous work (Brédas and Street (1985)) where the backbone-phenyl bonds were gauche with respect to the backbone (i′'-PS conformation). The theoretical UPS spectra produced by the i-PS and i′'-PS conformations present subtle yet significant differences which, when comparison is made to experiment, all point in favor of the i-PS conformation considered in this work. This resolves some of the discrepancies between theory and experiment from previous work.