Dynamical quantum filtering in hydrogen-surface reactions

We report on how surfaces that adsorb hydrogen could act as rotational quantum state filters and cause, for example, D-2 molecules desorbing in the vibrational ground state from Cu(111) to exhibit strong rotational alignment. For low final translational energies, we found that desorbing D-2 molecules have rotational alignment factor Values corresponding to cartwheel-type rotational preference. As the final translational energy increases, the corresponding alignment factor increases initially to values corresponding to helicopter-type rotational preference and then, eventually, decreases to values almost compatible with a spatially isotropic distribution, as the translational energy increases further. (C) 1998 Elsevier Science B.V. All rights reserved.