Identifying the Mineral Source of Phosphorus-Containing Molecules in Space

Only a few phosphorus-containing molecules have been identified in extraterrestrial environments, but the mineral source of these gas-phase molecules has yet to be identified. The objective of this project is to identify the conditions that cause small phosphorus-containing molecules to desorb from the surface of schreibersite, an iron-nickel phosphide mineral. To determine these conditions, we place a sample of schreibersite in an ultrahigh vacuum (UHV, with a pressure of less than 1 x 10-9 torr) chamber and measure its ability to react with small molecules (e.g., H2O, CH4, andCO2) using reflection-absorption infrared spectroscopy (RAIRS). While preparing to run these experiments, we encountered and troubleshot many issues that arose. One problem we ran into was the pressure not being low enough in the UHV chamber. We leak tested using a quadrupole mass spectrometer (QMS), found no leaks that were larger than 2 x 10-9 torr, but observed many peaks corresponding to hydrocarbons. To correct this, we disassembled the chamber, cleaning the interior with acetone, isopropanol, and then methanol. We also checked for metal shavings, loose pieces of fiberglass from the covering of our wires, and any other debris. Once everything was put back together, the pressure remained low enough to continue. Another issue we came across was the cooling of the sample. These experiments require temperatures of at least -173℃. This is crucial for small molecules to be able to stick to the surface of the schreibersite sample and to effectively model extraterrestrial environments like cometary coma and dense molecular clouds in the interstellar medium. To lower the temperature, we attached a cryogenic cooling system to the sample holder. The lowest temperature we’ve reached so far is -190.15℃ (83 K). Updates on sample imaging, RAIRS alignment, and preliminary data will also be presented