Negative ion properties of trans 2,2',6,6'-tetrafluoroazobenzene: Experiment and theory

Chemical bonding and the electronic structure of the trans 2,2',6,6'-tetrafluoroazobenzene negative ion have been studied using collision-induced dissociation as well as photodetachment-photoelectron spectroscopy and the experimental results for different properties were compared with the corresponding values calculated using ab initio quantum chemistry methods. The trans 2,2',6,6'-tetrafluoroazobenzene anion was prepared by atmospheric pressure chemical ionization for the collision induced dissociation (CID) experiment and through thermal electron attachment in the photodetachment-photoelectron spectroscopy experiments. The adiabatic electron affinity of trans 2,2',6,6'-tetrafluoroazobenzene was measured to be 1.3 ± 0.10 eV using 355 nm, 488 nm, and 532 nm photodetachment photons and the vertical detachment energy was measured to be 1.78 ± 0.10 eV, 2.03 ± 0.10 eV, and 1.93 ± 0.10 eV, respectively. The adiabatic electron affinity was calculated employing different ab initio methods giving values in excellent agreement with experimental results. Energy resolved collision induced dissociation experiment study of the precursor anion resulted in 1.92 ± 0.15 eV bond dissociation energy for the collision process yielding [C6H3F2](-) fragment ion at 0 K. Calculations using different ab initio methods resulted in a bond dissociation energy ranging from 1.79 to 2.1 eV at 0 K. Two additional CID fragment ions that appear at higher energies, [C6H2F](-) and [C6H](-), are not results of a single bond cleavage. The occurrence of [C6H](-) is of particular interest since it is the first anion to be observed in the interstellar medium.