The accurate ab initio MBPT quartic force field of Bartlett, Shavitt and Purvis has been fit to an analytical function using a method developed by Sorbie and Murrell (SM). An analysis of this surface indicates that it describes most properties of the H2O molecule very accurately, including an exact fit to the MBPT force field, and very close to the correct energy difference between linear and equilibrium H2O. The surface also reproduces the correct diatomic potentials in all dissociative regions, but some aspects of it in the "near asymptotic" O(1D) + H2 region are not quantitatively described. For example, the potential seems to be too attractive at long range for O + H2 encounters, although it does have the correct minimum energy path geometry and correctly exhibits no barrier to O atom insertion. Comparisons of this surface with one previously developed by SM indicates generally good agreement between the two, especially after some of the SM parameters were corrected, using a numerical differentiation algorithm to evaluate them. A surface developed by Schinke and Lester (SL) is more realistic than outs in the O(1D) + H2 regions, but less quantitative in its description of the H2O molecule. Overall, the present fit appears to be both realistic and quantitative for energy displacements up to 3-4; eV from H2O equilibrium, and should therefore be useful for spectroscopic and collision dynamics studies involving H2O.
ASJC Scopus subject areas
- Physics and Astronomy(all)
- Physical and Theoretical Chemistry