MOLECULAR ASTROPHYSICS. To understand how molecules form in space, earthbound scientists are performing laboratory experiments that simulate the cold interstellar dust and gas clouds where molecules are manufactured. Some researchers study the formation of H2, the universe's simplest and most abundant molecule. Other researchers study the properties of polycyclic aromatic hydrocarbons (PAHs), flat rings of carbon and hydrogen which seem to exist in the interstellar clouds. At the APS meeting, Gianfranco Vidali of Syracuse (315-443-9115) presented studies on how two hydrogen atoms join together on an interstellar dust grain. Shooting H atoms onto a solid target (playing the role of an interstellar dust grain, with a temperature of 10 K) and observing how many of the atoms would react on the cold surface to form molecular hydrogen, he and his colleagues found that the rate of H2 formation was higher on amorphous carbon than on olivine (a silicon-oxygen based material), suggesting that the former is a more likely candidate for interstellar dust, whose composition is still unknown. Louis Allamandola (650-604-6890) and his colleagues at NASA-Ames discussed recent experiments showing that shining UV light on PAHs can convert them to organic compounds that are present in henna, aloe, and St. John's wort. Combined with spectroscopic measurements that support the existence of PAHs in interstellar clouds, these experiments advance the notion that PAHs may be the precursors of biologically important molecules on our planet and possibly others.