Ortho/Para Ratio of Formaldehyde Formed in UV-Photolyzed Interstellar Ice Analogs

Interstellar molecules with symmetric hydrogen nuclei exist in ortho and para states and the ortho-to-para ratios (OPRs) are thought to provide information about thermal and chemical history. The OPR of formaldehyde (H₂CO) is sometimes used to predict whether this compound formed on a cold interstellar grain or in the gas phase at warmer temperatures, but the full meaning of the OPRs detected in interstellar clouds are still a topic of debate. This work aims to unravel more information about the OPR of formaldehyde (H₂CO) formed on icy interstellar grains through laboratory experiments using SubLIME, the Sublimation of Laboratory Ices Millimeter/submillimeter Experiment. The OPR of formaldehyde (H₂CO) was measured using submillimeter spectroscopy after low-temperature formation by ultraviolet photolysis of interstellar ice analog samples containing water (H₂O), carbon monoxide (CO), and/or methanol (CH₃OH). The experimental approach and preliminary results will be discussed.