Rationale for reagent reorientation in the activated bimolecular reaction N(2D)+H2:: Beyond the angular dependent line of center model

The reaction N(D-2)+H-2(X (1)Sigma (+)(g))--> NH(X (3)Sigma (-)(g))+H(S-2) involves an early barrier of similar to2 kcal/mol and a significant exoergicity of similar to 30 kcal/mol. Thus, for collision energies of several kcal/mol, barrier crossing leads to reaction with nearly unit probability. To our knowledge, the angular dependent line of center (ADLOC) model is to date the only one which allows the analytical formulation of the barrier overcoming cross section, identifiable here with the reaction cross section. This model, however, neglects the interaction between reagents up to the barrier top. As a consequence, it ignores the reorientation of H-2 with respect to N which enhances, on average, the reactivity with respect to its predictions. The linear transformation model (LTM), recently derived in order to describe product separation in unimolecular fragmentations, is now applied to the study of reagent approach in the title reaction. The main interest of LTM is to take into account reorientation while leading to an expression of the reaction cross section as simple as the ADLOC one, but in much better agreement with dynamical calculations. (C) 2001 American Institute of Physics.