Quantum dynamics of NH(a1Δ)+H reactions on the NH2 A 2A1 surface

We present the Born-Oppenheimer dynamics of the depletion reaction NH(a(1)Delta)+H(')-> N((2)D)+H(2) and of the exchange one NH(a(1)Delta)+H(')-> NH(')(a(1)Delta)+H, using the real wavepacket and flux methods and an accurate NH(2)(A (2)A(1)) surface. We report coupled-channel reaction probabilities, cross sections, and rate constants, taking into account Coriolis couplings. Because the surface is barrierless and strongly bound, probabilities have small centrifugal thresholds and present sharp and large resonances, associated with long-lived collision complexes. Large J's enhance the high-energy reactivity and favor the exchange reaction, owing to the negative Coriolis couplings, and to K that inhibits depletion but not exchange. Coriolis couplings are important in the collision complexes, and the centrifugal sudden approximation thus gives large errors. Cross sections are large at the threshold and minimal at intermediate collision energies and increase moderately at larger energies. Exchange is preferred, and both reactions are inhibited by the NH rotational excitation. Finally, the present rate constants are in good agreement with previous experimental and semiclassical results.