Potential energy surface and quasiclassical trajectory studies of the N(D-2)+H-2 reaction

We present a global potential energy surface for the 1A " state of NH2 base d on application of the reproducing kernel Hilbert space interpolation meth od to high quality ab initio (multireference configuration interaction! res ults. Extensive quasiclassical trajectory calculations are performed on thi s surface to study the N(D-2) + H-2/D-2 reaction dynamics. Comparison is ma de with calculations on the lower level [first order configuration interact ion (FOCI)] surface of Kobayashi, Takayanagi, Yokoyama, Sato, and Tsunashim a (KTYST). We find a saddle point energy of 2.3 (1.9) kcal/mol for the perp endicular approach for the second order configuration interaction (SOCI) (S OCI with Davidson correction) surfaces, and a collinear stationary point en ergy of 5.5 (4.6) kcal/mol. The ordering of these stationary points is reve rsed compared to the corresponding FOCI results, and the only true reaction path on our surface is perpendicular. The primary reaction mechanism is de termined to be C-2v insertion to produce short lived (100-300 fs) NH2 inter mediates. Angular distributions are found to be primarily forward-backward symmetric, with a slight bias towards backward scattering at low energies. Decay of the NH2's occurs before energy is fully randomized, so the product vibrational distributions are a little hotter than statistical-with vibrat ional population ratios NH(v "=1)/NH(v "=0)=0.8 and ND(v "=1)/ND(v "=0)=0.9 (near threshold). These ratios, and other aspects of the vibrational produ ct distributions are in excellent agreement with recent laser induced fluor escence studies. (C) 1999 American Institute of Physics. [S0021-9606(99)022 17-5].