THE STEREODYNAMICS OF MOLECULES, the orientation and movement of molecules in three-dimensional space, plays a large role in chemical reactions. As with cosmonauts approaching their space station, some maneuvers are more effective than others in producing a successful docking. In the case of diatomic hydrogen molecules approaching a copper surface, an IBM Almaden/UC Santa Barbara collaboration has shown that the molecules have a much better chance of crash landing and then sticking to the surface if the plane of the molecule (traced out by the mutual orbit of the two atoms about each other) is parallel to the surface. The reaction process was also observed to favor certain molecule kinetic energies over others. Quantitative studies of stereo preferences should lead to a better understanding of catalysis and other industrially important processes where chemical reactions are influenced by nearby surfaces. (H. Hou et al., Science, 4 July 1997.)