Electronic absorption spectra of linear C6Br and C6Br+ in neon matrices

Electronic absorption spectra of linear C6Br+ and C6Br have been recorded in 6 K neon matrices. Two strong absorption systems starting at 555.1 nm and 539.3 nm are assigned to the 1 2Π ← X 2Π electronic transition of C6Br, and 1 3Σ− ← X 3Σ− of C6Br+. Excitation of normal modes along with overtones and combination bands in the excited electronic state are observed. Assignments are based on mass-selection, photobleaching behavior, comparison with the known electronic transitions of linear C6Cl and C6Cl+, and excitation energies obtained with CASPT2 and SAC-CI theory as well as on computed vibrational frequencies.