Replacing one of the hydrogen atoms of Bz by a bromine atom lowers the D6h point-group symmetry of neutral Bz to C2v, and also lifts the near-degeneracies between the six core orbitals of the carbon atoms. In particular, the Br atom increases the transition energy of the carbon atom bonded to the bromine atom, here labeled as C*. The two highest occupied molecular orbitals, π(6b2) and π(2a2), result from a splitting of the highest degenerate π orbitals of Bz. The highest occupied molecular orbital (HOMO) π(6b2), with the lowest binding energy of 8.992 eV, shows partial bromine character. The major electron density of the π(6b2) orbital is distributed among several atoms, the C* atom (0.46), the C atom that is in the para position to C* (0.5), the Br atom (0.47) and among the other C atoms (0.56). The next lower π(2a2), orbital of BrBz is noticeably shifted to lower energy (i.e., to higher binding energy, 9.663 eV) compared to the parent π orbital of Bz. The next two lower molecular orbitals are 11b1 (σBr-type) and 5b2 (πBr-type) that are related to the 4p bromine lone pair orbitals, which are split due to the interaction with the benzene ring. The ionization energies from these two orbitals are 10.633 eV and 11.188 eV, respectively. The bromine atom affects the core level transition energies as well. Previous studies have shown that the 1s orbital of the carbon atom (C*) nearest to the bromine atom is shifted to higher binding energy by about 1.1 eV relative to the 1s orbitals of the other carbons (C), as shown in the orbital diagram of BrBz in Figure . The splitting of the other 1sC orbitals due to lower symmetry of the benzene ring is much smaller. The different electron distribution in the valence and core levels due to bromine attachment leads to several changes in the x-ray spectrum of neutral BrBz compared to Bz. The major change appears as a new peak related to the 1sC*→π* transition shifted to higher energy by about 1.1 eV from the most intense peak that corresponds to the 1sC→π* transition, which is similar to the 1sC→π* transition in the x-ray spectrum of neutral Bz.