As comets zoom through sun-irradiated space, they emit unstable molecules and atoms called free radicals. By tracing the molecular origins of these free radicals, scientists can determine the original composition and source of the comets -- which in turn may lead to clues about the origin of the solar system. Parent molecules for most of the free radicals have been found, a birthing process called one-step solar photolysis. Until recently though, the origins of the C2 and C3 radicals in comet emissions have mystified researchers. Nearly 20 years ago, UC Davis chemistry professor William M. Jackson proposed that the C2 radicals come from a two-step process. At this year's ACS meeting, Jackson and his research group will present four papers that may prove his original postulate true, as well as contribute insights into the photochemical processes of small free radicals. Basically, in the two-step process, one photon from the sun zaps the parent molecule (C2H2), and another photon blast creates the C2 radical. Similarly, the C3 radical comes from a two-step photolysis from either of two parent molecules (C3H4 and CH3C2H). During the laboratory recreation of the C3 radicals, Jackson found the stuff that links solar systems to interstellar clouds. The molecule formed at the halfway point in the birth of C3 radicals is one of the most common species found in interstellar clouds. Consistent with other evidence, this finding links the chemistry of comets to the raw material that astronomers believe also forms planets and suns. The papers will be presented at poster sessions Wednesday, April 8, 7-10 p.m., Sheraton Palace.