Angle-resolved photoemission spectroscopy (ARPES) and optical measurements were performed on single crystal samples of ZrSe3, HfSe3, and ZrS3, which belong to the class of low-dimensional band insulators. By ARPES, we traced the dispersion of the (S 3p, Se 4p) p-derived valence states. In all cases, the topmost band exhibits energy splitting increasing from S to Se, which we attribute to the spin-orbit interaction, similar to recent observations in the related layered dichalcogenides. The combination of optical and photoemission results allows us to address the issue of the gap feature in the absorption spectra and to characterize the electronic and vibrational properties of ZrSe3, HfSe3, and ZrS3.