A three-dimensional potential energy surface for the reaction N+(3P)+H2(1 Σ+g) = NH+ (X 2Π)+H(2S).

Extensive ab initio calculations have been performed on the reaction N+3(P)+H21(Σ+g)NH+ (X 2Π)+H(2S), using complete-active-space self-consistent-field and multireference contracted configuration interaction methods. The 752 calculated energy points belonging to the 1 3A‘ surface were fitted to an analytical potential energy surface, with an average least-squares deviation of only 0.026 eV (2.5 kJ/mol). A key to this accurate fit of the surface, which does include minima as deep as 6 eV, is the use of R-n polynomials in the asymptotic region, and Rn polynomials in the deep minima regions. The calculated reaction endothermicity is 0.03 eV, after correcting for the differences in zero point vibrational energies. This is in agreement with the essentially thermoneutral reaction enthalpy, obtained in recent experiments. An important feature of the potential energy surface is the anisotropy in the reactant channel, arising from the ion–quadrupole interaction. [ABSTRACT FROM AUTHOR]