HOW THREE HYDROGEN IONS SHARE THEIR ENERGY and how they position themselves with respect to each other has been experimentally measured for the first time, shedding light on the infamous "three-body problem" in the realm of electrically charged particles. Although physics can make exact predictions on the forces between two objects (such as the Earth and the Sun), it can only approximate the considerably more complicated case of three interacting objects (like the Earth-Sun-Moon) or, similarly, three electrically charged particles experiencing the Coulomb force, the "electrostatic" force that particles exert on each other because of their electrical charge. Previous experiments have investigated the Coulomb interactions among two electrons and a positive ion; however, such situations can be easily approximated as a two-body problem because the much heavier ion remains relatively stationary. At next week's APS meeting (paper K5.03), Lisa Wiese of the University of Nebraska (402-472-2786) will describe a technically difficult study of the Coulomb interactions between three charged particles with roughly equal mass. Smashing the molecular ion H₃⁺ against a helium target produces three ions: H⁺, H^-, and H⁺. Measuring the energies of all three particles and their angles as they emerged from the target, the physicists deduced that the H^- tended to reside in between the two H⁺ ions, from near the "Coulomb saddle point" (where the forces from the other hydrogen ions balance out) to the near vicinity of an H⁺ ion. Interestingly--and in contrast to all theoretical assumptions--the H^- was never found at the saddle point itself. (See the figure at Physics News Graphics; see also L.M. Wiese, Phys. Rev. Lett., 22 Dec. 1997).