DOUBLE MANY-BODY EXPANSION POTENTIAL-ENERGY SURFACE FOR GROUND-STATE HO3

We report a single-valued double many-body expansion potential energy surface for the ground electronic state of HO3 which has been calibrat ed at short range from newly calculated ab initio energies including e lectron correlation. The long-range part of the potential surface incl udes the electrostatic energy up to four-body terms, while the dynamic al correlation has been truncated at the three-body level. The main at tributes of the HO3 double many-body expansion potential energy surfac e have also been characterized. The latter are found to be in generall y good agreement with those from the reported ab initio energies, and also with the results from previous theoretical calculations. For the H + O-3 reaction, the novel potential energy surface shows no activati on barrier, while predicting a metastable HO3 structure with respect t o the separated HO + O-2 products. A quasiclassical trajectory study o f the H + O-3 --> HO + O-2 reaction has also been carried out, and the calculated thermal rate coefficients shown to be in good agreement wi th the experimentally determined values.