Electron states of benzene-Br₂ donor-acceptor complex: HeI photoelectron spectroscopy and ab initio molecular orbital study

Abstract

HeI photoelectron spectrum of weakly bonded π-donor complex of benzene with Br₂ is obtained. Benzene orbitals are shifted to higher binding energy by 0.25 eV and the bromine orbitals to lower binding energy by about 0.5 eV due to the complex formation. Ab initio molecular orbital calculations predicted a weak π→σ complex between benzene and bromine having a C_6v symmetry. The charge transfer is from the benzene π cloud to the bromine orbital. The magnitude of charge transfer computed from natural bond orbital analysis is 0.002.