  We have performed a comparative study of the electronic structures of the
spin-Peierls systems TiOCl and TiOBr by means of photoemission spectroscopy and
density functional calculations. While the overall electronic structure of
these isostructural compounds is qualitatively similar, the bromide appears to
be less one-dimensional. We present a quantitative analysis of the experimental
dispersions in terms of exchange constant J and hopping integral t as well as a
discussion of the qualitative spectral features. From that we conclude that
despite the one-dimensional physics triggering the ground state in both
compounds a proper description of the normal state electronic structure has to
take into account the anisotropic frustrated interchain interactions on the
underlying triangular lattice.
