Probing the Unusual Chemistry of Interstellar Phosphorus
Molecular Physics seminar
Monday 18 August 2008
to 11:00 at
Prof. Lucy M. Ziurys (University of Arizona)
The element phosphorus is something of an enigma. While it only ranks as the 18th most abundant element, cosmically, it is the 5th most prevalent element in living systems. The biological importance of phosphorus is attributed to exogenous delivery by meteorites, and thus its interstellar origin. Until very recently, little was known about the carriers of this element in dense molecular interstellar gas. Although atomic measurements towards diffuse clouds suggested that phosphorus was not depleted, only two P-bearing molecules had ever been identified in denser gas: PN, detected in molecular clouds, and CP, found in circumstellar gas around the evolved star IRC+10216. The chemistry of interstellar phosphorus was therefore extremely limited. Over the past year, however, four new phosphorus-containing molecules have been discovered in circumstellar gas using millimeter and sub-mm astronomy: PO, HCP, PH3, and CCP. The source list has been extended to other C-rich envelopes and O-rich ones as well. Several of these detections were made using the Arizona Radio Observatory’s Sub-Millimeter Telescope (SMT), using new receivers with sideband-separating SIS mixers – technology developed for the Atacama Large Millimeter Array (ALMA). New laboratory spectroscopy studies also made some of this work possible. Phosphorus chemistry now appears to be more complex than previously thought. The abundances and distributions of phosphorus-containing molecules in interstellar and circumstellar gas will be discussed, as well as possible synthetic schemes. The possible connection to meteoritic material will also be reviewed.