Halogen substituted acetic anhydrides: A HeI photoelectron spectroscopy and theoretical study

The HeI photoelectron spectra of acetic anhydride and halogen substituted acetic anhydrides: CH3C(O)OC(O)CH3, CH3C(O)OC(O)CCl3, CH3C(O)OC(O)CF3 and CF3C(O)OC(O)CF3 are obtained and analyzed. Geometry optimizations of the structure for stable conformers are performed at different levels of theory (HF/6-31G(d), B3LYP/6-31G(d), B3LYP/6-311G(d), B3LYP/6-311+G(d)), and the vertical ionization energies are calculated by using orbital valence Green's functional (OVGF). The experimental first vertical ionization potentials for the four molecules are 10.73, 11.06, 11.53 and 12.21 eV, respectively. The electronic withdrawing effects are clearly reflected in this series of compounds. The highest occupied molecular orbital (HOMO) for each compound is mainly the carbonyl oxygen lone pair (nO) ({13b(nO)}−1, {51a(nO, nCl)}−1, {39a(nO)}−1 and {25b(nO)}−1, respectively). Calculations of the corresponding radical-cationic forms are carried out in order to compare their properties with those of the neutral molecules. All calculations predict the (s, s) conformer is energetically favorable for all molecules investigated, and adopts a planar structure after ionization.