Potential energy surface for H2O((3)A(")) from accurate ab initio data with inclusion of long-range interactions.

A new potential energy surface for the O((3)P) + H(2) system in the lowest (3)A(") state is built using ab initio data calculated by Rogers et al. [J. Phys. Chem. A 104, 2308 (2000)] and the double many-body expansion formalism. It incorporates a semiempirical model of long-range interactions, which should play an important role at low collision energies. Preliminary quasiclassical trajectory results at 12.6 kcal/mol collision energy, show that the deeper van der Waals region described in this new surface translates into a four times higher cross section than that of Rogers' (3)A(") surface. To confirm this hypothesis, a second surface was calibrated. The two surfaces are fitted with rmsd<0.5 kcal/mol and differ mainly on the depth of the van der Waals region. That difference in the van der Waals region corresponds to a 22% lower cross section of the less deep surface, which is still three times higher than the equivalent results from Rogers' (3)A(") surface. This study reflects the importance of a correct description of van der Waals forces on potential energy surfaces.