PR Focus

Physical Review Focus is a FREE APS electronic journal featuring selections from Physical Review Letters explained at a level accessible to all physicists. The editor is David Ehrenstein [see April 1998 APS News]. APS News is printing samplings from PR Focus to introduce the membership to this new journal. To receive one-paragraph introductions (such as the one below) each week by e-mail, send a blank message to join-focus@aps.org, or go to the list .

Orientations made easy. Based on their fluorescence patterns, researchers can distinguish single molecules that are primarily xy-aligned (left) from those primarily z-aligned (right).Robert M. Dickson / Georgia Institute of Technology

Orienting Single Molecules

Physicists have developed many methods for observing the average properties of large collections of molecules, researchers have only recently managed to detect individual molecules. For example, attaching a highly fluorescent dye to a large protein molecule allows biophysicists to learn about details of the conformational changes that occur when the protein carries out its biological function. Now a team reports in the 14 December PRL a method for distinguishing the orientation of such a fluorescent molecule in a direct way. The technique may also be useful in understanding the structures of polymer matrices and other materials. (R. M. Dickson et al., Phys. Rev. Lett. 81, 5322; see complete PR Focus story posted online 15 December 1998.)

Crystalline bouncer. Hydrogen molecules with different nuclear spin alignments rebound differently from the surface of a lithium fluoride crystal. The results can reveal details of the surface electric field.Joseph Lauher/SUNY Stony Brook

Nuclei Affect Bounce of H₂

A molecule's atomic nuclei don't usually have much effect on its interactions with other atoms and molecules. Chemical reactions, for example, involve only the external electrons. But the alignment of the nuclear spins can affect the rotation of a diatomic molecule like H₂. Now a report in the 21 December PRL shows that this alignment strongly affects even a simple scattering experiment, where hydrogen molecules bounce off the surface of a crystal. The experiment may also provide a new method for probing the electric field structures of surfaces. (M. F. Bertino et al., Phys. Rev. Lett. 81, 5608; see complete PR Focus story posted online 22 December 1998.)