VUV photoprocessing of oxygen-containing polycyclic aromatic hydrocarbons: Threshold photoelectron spectra

Abstract Oxygen-containing polycyclic aromatic hydrocarbons (OPAHs) have been considered as potential carriers of the 11.3 μm band in interstellar observations. To begin to probe their contribution chemistry medium, we report here threshold photoelectron spectra (TPES) for seven oxygen-containing 2,3-benzofuran (BF), 2,3-dihydrobenzofuran (DHF), phthalan (PH), dibenzofuran (DBF), dibenzo(B,F)oxepine (DBO), benzo[b]naphtho[2,3-d]furan (BNF) and benzo[b]naphtho[1,2-d]furan (cBNF). Vertical ionization energies ground excited ion states were calculated with outer-valence Green’s function method, Franck–Condon simulations, based on harmonic (time-dependent) density functional theory results, used explore vibrational excitation upon ionization. CBS-QB3 calculations are also reported. Adiabatic (IE) could be measured accurately five molecules: BF (8.35 ± 0.01 eV), PH (8.76 ± 0.01 eV), DBF (8.12 ± 0.02 eV), BNF (7.64 ± 0.02 eV), cBNF (7.62 ± 0.02 eV). For cBNF, state optimizations allowed simulations excited-state bands. The TPES DHF DBO feature broad onsets due large geometry changes ionization, both become planar when an electron is removed. maxima yield vertical IE these two 8.2 ± 0.2 eV 8.0 ± 0.2 eV, respectively, while best estimate adiabatic 7.98 ± 0.05 eV.