TC12		15min11:45

P. HASSANZADEH AND K. K. IRIKURA, Physical and Chemical Properties Division, National Institute of Standard and Technology, Gaithersburg, MD 20899.

Ab initio internuclear distances and anharmonic constants for IO, IO^-, and IO⁺ were calculated at the CCSD(T) level using 6-311+G(3df,2p) basis sets. The reliability of the calculations was tested against the available experimental values for IO and IO^-.

Electronic energies were also calculated at the CCSD(T) level using the 6-311+G(3df,2p) basis sets, Sadlej's polarized basis sets (PBS), and Wadt and Hay's effective core potential (ECP) basis sets at the experimental geometries and corrected by the experimental zero-point vibrational energies. The enthalpy of formation of the hypoiodite anion IO^- (¹⁺) (_fH₀^o -109 \pm 5 kJ/mol, uncertainties are 2) was obtained from ab initio energetics for the metathesis reactions IO^- + Cl^- -> ClO^- + I^- and IO^- + Cl₂ -> ClO^- + ICl. The reliability of the computational procedure was tested by performing analogous calculations for BrO^- and comparing the results with the accepted value for the enthalpy of formation of BrO^-.

The enthalpy of formation for IO (X²_3/2 (_fH₀^o = 120 \pm 5 kJ/mol) was deduced from the calculated _fH₀^o(IO^- ) and the experimental electron affinity of IO (EA = 229.43 \pm 0.06 kJ/mol) measured by Gilles et al.. The enthalpy of formation of IO⁺(^3-) (_fH₀^o = - 1060 \pm 5 kJ/mol) was also derived from the present enthalpy of formation of IO and the experimental adiabatic ionization energy of IO (IE = 939.4 \pm 1.7 kJ/mol) measured by Zhang et al. The corresponding bond dissociation energies are D₀^o(IO)= 167 \pm 5 kJ/mol, D₀^o(IO) = 234 \pm 5 kJ/mol, and D₀^o(IO⁺)= 303 \pm 5 kJ/mol.

JANAF-style thermodynamic functions for IO, IO^-, and IO⁺ from 0 to 1000 K are also tabulated.