The molecular structures, relative energies, vibrational frequencies, and electron affinities for the Cl2On/Cl2O (n = 1–4) systems have been investigated using hybrid Hartree–Fock/density functional theories (BHLYP and B3LYP) and pure density functional theories (BP86 and BLYP). The three different types of neutral/anion energy differences reported in this research are the adiabatic electron affinity (EAad), the vertical electron affinity (EAvret), and the vertical detachment energy (VDE). The basis set used in this work is of double-ζ plus polarization quality with additional s- and p-type diffuse functions, and it is denoted DZP++. The geometries are fully optimized by all four DFT methods. We have predicted a number of possible low-lying local minima, including some that are unprecedented. Most strikingly, in several cases structures that have been observed in the laboratory turn out not to be lowest in energy for a particular chemical composition. Two structures are predicted with a formally seven-coordinate chlorine atom. The global minima for the Cl2On/Cl2O (n = 1–4) systems are ClOCl (C2v), ClClO− (Cs), ClOOCl (C2), OOCl (C2v), ClOOOCl (C2/C1), ClO(O2)Cl− (Cs),trans-ClO(O2)OCl (Ci), and trans-ClO(O2)OCl− (Ci), respectively. The relative energies of the different minima are reported. Five of the 42 structures predicted here have been determined experimentally. Our theoretical geometries and vibrational frequencies are carefully compared with the limited available experimental results, and the BHLYP functional in general provides the best agreement. The ClClO− and ClClO ground states might be regarded as Cl− … ClO and Cl− … ClO2 complexes, respectively. The adiabatic electron affinities, obtained at the favored DZP++ BLYP level of theory, are 3.12 eV for Cl2O, 3.96 eV for Cl2O2, 3.66 eV for Cl2O3, and 4.15 eV for Cl2O4. The adiabatic EAs for the first three systems are similar to those of Br2On (3.14, 3.80, and 3.46 eV with BLYP for Br2On, n = 1–3), and this may reflect the geometric similarity between these bromine and chlorine species. But, EAad for Br2O4 (1.97 eV) is different from Cl2O4 because the neutral and anionic bromine species have different global minimum geometries from those for Cl2O4. © 2003 Wiley Periodicals, Inc. Int J Quantum Chem, 2003
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