Diagram of the H3+ molecule (top circle) and its breakup into three distinct particles (bottom circle)--H+, H-, and H+. The H3+ molecule contains three protons (indicated by "+" signs in the diagram). When the three protons of H3+ are less than 10 atomic units apart (where 1 a.u. is equal to the size of the hydrogen atom), they are in what is called the "reaction zone." While in the reaction zone, the protons share the two electrons in the molecule, and form strong "covalent bonds." Since the electrons are sort of "spread out" among the protons, the H3+ system must be described by the laws of quantum mechanics, the modern theory of matter and energy at the atomic and molecular scale.
As the protons spread out (indicated by the v's with arrows--these are called "velocity vectors") and the system increases in size, both electrons coalesce with a single proton, forming H-. Beyond a physical size of ~10 a.u, the H- can be identified as a distinct particle and the two remaining protons can be considered as distinct particles. In fact the protons can be thought of as H+ ions--hydrogen is just a proton plus an electron, and H+ is simply a hydrogen with the electron removed. The three particles--H+, H-, and H+--act as distinct objects and can be explained to a great extent by the laws of classical physics. They interact with one another and form what is known as a "three-body system." The H+, H-, and H+ interact via the Coulomb force, the "electrostatic" force that particles exert on each other because of their electrical charge.
This research will be reported in paper K5.03 of the 1998 Annual Meeting of the Division of Atomic, Molecular, and Optical Physics (DAMOP), to be held between May 27-30 in Santa Fe, New Mexico.
See also L.M. Wiese, O. Yenen, B. Thaden, and D.H. Jaecks, "Measured Correlated Motion of Three Massive Coulomb Interacting Particles," in Physical Review Letters, v. 79, no. 25, 22 December 1997.
Link to related Physics News Update item (available May 20, 1998)