UNUSUAL PROPERTIES OF CUBANE. Synthesized first in 1964, cubane (C₈H₈) is a molecule consisting of 8 carbon atoms arranged at the corners of a cube plus single hydrogen atoms sprouting symmetrically from each carbon (see the figure at Physics News Graphics). The C-C-C bond angle is therefore 90 degrees, rather than the 109.5 degrees customary in other hydrocarbon molecules. Because of this a great deal of strain energy is stored in the chemical bonds---150 kcal/mole or 6.5 eV per molecule. Replace all the H's with NO₂ groups and you get a terrific fuel or explosive (with nearly twice the power of TNT). Replacing the H's with other chemical groups results in potentially more salubrious derivatives, some of which are currently undergoing tests in the fight against the AIDS virus, bone marrow cancer, and Parkinson's disease. For all its potential, however, solid cubane is not well understood. Like other molecular solids (materials such as C₆₀ in which molecules rather than atoms compose the underlying lattice), cubane exhibits a "plastic phase" (close to its melting point) in which the molecules start to swivel about one or more of their axes. Recently, a Chicago-NIST collaboration has experimentally worked out the structure of this plastic phase by sending x rays and neutrons through powdered samples. Surprisingly, unlike most other molecular solids, the plastic phase of cubane is not cubic. The researchers' work includes a model of the intermolecular interactions that correctly predicts this structure, which could speed up future applications of this novel molecule. (T. Yildirim et al.,upcoming article in Physical Review Letters. Contact Peter Gehring at NIST, peter@rrdstrad.nist.gov, 301-975-3946. Journalists can obtain copies of the article from physnews@aip.acp.org)

THE EARTH HAS A COMPANION IN ADDITION TO THE MOON. The object, asteroid 3753, is in orbit not around the Earth but in concert with it in a horseshoe-shaped trajectory that co-rotates with the Earth in its orbit around the sun; with respect to the sun, the trajectory is an eccentric ellipse somewhat inclined to the ecliptic plane. The discovery in 1906 of such an asteroid, 588 Achilles, near Jupiter, confirmed Joseph-Louis Lagrange's theory that planet-sun systems have points (now called Lagrangian points) where a third object of negligible mass could reside in stable equilibrium. Many such captive asteroids have been since found near our planetary neighbors, but only two of them, Janus and Epimetheus (companions of Saturn) have horseshoe orbits. Asteroid 3753, 5 km in diameter, was first spotted in 1986, but its trajectory was not understood until now with the numerical modeling research of astronomers at York University (Ontario) and the University of Turku (Finland). (Paul Wiegert et al., Nature, 12 June 1997.)

GAMMA RAYS FROM A FREE ELECTRON LASER. Physicists at Duke University scatter ultraviolet photons from 500-MeV electrons inside a free electron laser facility to produce 12-MeV gamma-ray photons. By collimating the gamma flux, one can achieve a nearly monoenergetic beam. The emittance (the divergence) of the beam is so low that even after collimation the intensity of the gamma beam is 1000 times greater than that produced with conventional laser systems. A beam like this will be useful for cancer therapy and for high-precision gamma-ray transmission radiography. It can also be used to produce positrons and to perform sensitive studies of the atomic nucleus. ( Phys. Rev. Lett., 16 June.)