ADIABATIC ELECTRON-AFFINITIES OF SMALL SUPERHALOGENS - LIF2, LICL2, NAF2, AND NACL2

Geometries and frequencies for the neutral MX2 and ionic MX2- species (M=L1, Na, and X=F, Cl) 2 are studied by several theoretical methods: density functional theory (Becke-3-Lee-Yang-Parr) [DFT(B3LYP)], second -order many-body perturbation theory [MBPT(2)], and coupled-cluster wi th singles and doubles (CCSD). The geometries optimized at the CCSD/6- 311+G(d) level are used in CCSD(T) calculations with a large atomic na tural orbital basis to compute adiabatic electron o affinities (EA(ad) ), which are found for LiF2, LiCl2, NaF2, and NaCl2 to be 5.45, 4.97, 5.12, and 4.69 eV, respectively. The highest EAs among all the atoms o f the periodic table occur in the halogen atoms (fluorine, 3.40 eV; ch lorine, 3.62 eV); therefore all four of these triatomic radicals are p roperly termed superhalogens. LiF2, LiCl2, NaF2, and NaCl2 are thermod ynamically stable, and their dissociation energies computed at the CCS D with the noniterative inclusion of triples [CCSD(T)] level are 20.5, 24.9, 19.3, and 25.2 kcal/mol, respectively. LiF2-, LiCl2-, NaF2-, an d NaCl2- are more stable than their neutral parents with CCSD(T) disso ciation energies of 69.5, 58.7, 49.0, and 52.5 kcal/mol, respectively. The computed vertical electron detachment energies of LiF2-, LiCl2-, NaF2-, and NaCl2- are 6.51, 5.88, 6.18, and 5.77 eV, respectively, whi ch are in nice agreement with the values calculated by Scheller and Ce derbaum by the Green-Function method. (C) 1997 American Institute of P hysics.