Photoelectron spectra of 1,2-dithiin are assigned with ab initio electron propagator calculations of vertical ionization energies and corresponding Dyson orbitals. Close agreement with experimental peaks obtains for the first nine final states. Dyson orbitals for the first three vertical ionization energies are composed chiefly of sulfur 3p and butadiene pi fragment orbitals. Constructive interference between the second highest occupied pi orbital of butadiene and sulfur 3p orbitals is seen in the Dyson orbitals pertaining to the fourth and seventh ionization energies. Weak sigma bonding between sulfur atoms is found in the Dyson orbital for the fifth final state.