Dynamical Stereochemistry on Several Electronic States: A Computational Study of Na* + H2


The orbital control of stereochemistry is discussed with special reference to the Na (3p 2P) + H2 collision. As seen by H2, the p orbital of the electronically excited Na atom is like a quadrupole, which may or may not lock along the molecular axis. Quantum mechanically, variations in the alignment of the orbital represent changes in the electronic state of the system and so dynamical methods which allow for such interstate transitions must be used. A new, time dependent quantum mechanical method for propagating the wave function on several electronic states is used to study these interstate transitions. Particular attention is given to the question of orbital following. The computational method is fully quantum mechanical but it uses a basis set which takes full account of the classical motion on any given electronic state while the solution of the Schrödinger equation addresses the electronic-state-changing transitions. We pay specific attention to the orbital alignment for both cold and rotationally warm H2 and for low and high impact parameters throughout the course of the collision. It is concluded that orbital locking is not necessarily instantaneous and can lag behind the faster nuclear motion, including the (fast) rotational motion of H2.

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