Photoelectron spectroscopy of polyhalobenzenes

The electronic structure of several polyhalobenzenes (C6H3Br3 and C6H2XYZ2) has been investigated by HeI/HeII photoelectron spectroscopy. The spectra were assigned by Green's functions calculations and comparison with the spectra of related halobenzenes. The careful analysis of shifts in π-orbital and halogen lone pair ionization energies vs. related halobenzenes was made. This enabled us to analyze complicated substituent effects in greater detail than is possible by performing calculations of total energies for isodesmic reactions. The use of two descriptors enables one to estimate relative magnitudes of resonance and inductive effects and to demonstrate the presence of halogen-halogen interactions via π-system relay.