Double-valued potential energy surface for H2O derived from accurate ab initio data and including long-range interactions

Rio, Carolina; Brandão, J.

http://hdl.handle.net/10400.1/5377

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Authors

Rio, Carolina

Brandão, J.

Abstract(s)

In a recent work we have been able to model the long-range interactions within the H2O molecule. Using these long-range energy terms, a complete potential energy surface has been obtained by fitting high-quality ab initio energies to a double-valued functional form in order to describe the crossing between the two lowest-potential-energy surfaces. The two diabatic surfaces are represented using the double many-body expansion model, and the crossing term is represented using a three-body energy function. To warrant a coherent and accurate description for all the dissociation channels we have refitted the potential energy functions for the H2(3Su 1), OH(2P), and OH(2S) diatomics. To represent the three-body extended Hartree–Fock nonelectrostatic energy terms, V1 , V2 , and V12 , we have chosen a polynomial on the symmetric coordinates times a range factor in a total of 148 coefficients. Although we have not used spectroscopic data in the fitting procedure, vibrational calculations, performed in this new surface using the DVR3D program suite, show a reasonable agreement with experimental data. We have also done a preliminary quasiclassical trajectory study ~300 K!. Our rate constant for the reaction O(1D)1H2(1Sg 1) !OH(2P)1H(2S), k(300 K)5(0.99960.024)310210 cm3 molecule21 s21, is very close to the most recent recommended value. This kinetic result reinforces the importance of the inclusion of the long-range forces when building potential energy surfaces.