The highly exothermic hydrogen abstraction reaction H₂Te + OH → H₂O + TeH: comparison with analogous reactions for...

The "gold standard" CCSD(T) method is adopted along with the correlation consistent basis sets up to aug-cc-pV5Z-PP to study the mechanism of the hydrogen abstraction reaction H₂Te + OH. The predicted geometries and vibrational frequencies for reactants and products are in good agreement with the available experimental results. With the ZPVE corrections, the transition state in the favorable pathway of this reaction energetically lies 1.2 kcal mol^-1 below the reactants, which is lower than the analogous relative energies for the H₂Se + OH reaction (-0.7 kcal mol^-1), the H₂S + OH reaction (+0.8 kcal mol^-1) and the H₂O + OH reaction (+9.0 kcal mol^-1). Accordingly, the exothermic reaction energies for these related reactions are predicted to be 47.8 (H₂Te), 37.7 (H₂Se), 27.1 (H₂S), and 0.0 (H₂O) kcal mol^-1, respectively. Geometrically, the low-lying reactant complexes for H₂Te + OH and H₂Se + OH are two-center three-electron hemibonded structures, whereas those for H₂S + OH and H₂O + OH are hydrogen-bonded. With ZPVE and spin-orbit coupling corrections, the relative energies for the reactant complex, transition state, product complex, and the products for the H₂Te + OH reaction are estimated to be -13.1, -1.0, -52.0, and -52.6 kcal mol^-1, respectively. Finally, twenty-eight DFT functionals have been tested systematically to assess their ability in describing the potential energy surface of the H₂Te + OH reaction. The best of these functionals for the corresponding energtics are -9.9, -1.4, -46.4, and -45.4 kcal mol^-1 (MPWB1K), or -13.1, -2.4, -57.1, and -54.6 kcal mol^-1 (M06-2X), respectively.