Molecular structures, thermochemistry, and electron affinities for the dichlorine oxides: Cl₂O_n/Cl₂O (n = 1–4)

The molecular structures, relative energies, vibrational frequencies, and electron affinities for the Cl₂O_n/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 (EA_ad), the vertical electron affinity (EA_vret), 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 Cl₂O_n/Cl₂O (n = 1–4) systems are ClOCl (C_2v), ClClO⁻ (C_s), ClOOCl (C₂), OOCl (C_2v), ClOOOCl (C₂/C₁), ClO(O₂)Cl⁻ (C_s), trans‐ClO(O₂)OCl (C_i), and trans‐ClO(O₂)OCl⁻ (C_i), 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 Br₂O_n (3.14, 3.80, and 3.46 eV with BLYP for Br₂O_n, n = 1–3), and this may reflect the geometric similarity between these bromine and chlorine species. But, EA_ad 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