Formation of Glyoxylic Acid in Interstellar Ices: A Key Entry Point for Prebiotic Chemistry

With nearly 200 molecules detected in interstellar and circumstellar environments, the identification of the biologically relevant α-keto carboxylic acid, glyoxylic acid (HCOCOOH), is still elusive. Herein, the formation of glyoxylic acid via cosmic-ray driven, non-equilibrium chemistry in polar interstellar ices of carbon monoxide (CO) and water (H₂ O) at 5 K via barrierless recombination of formyl (HCO) and hydroxycarbonyl radicals (HOCO) is reported. In temperature-programmed desorption experiments, the subliming neutral molecules were selectively photoionized and identified based on the ionization energy and distinct mass-to-charge ratios in combination with isotopically labeled experiments exploiting reflectron time-of-flight mass spectrometry. These studies unravel a key reaction path to glyoxylic acid, an organic molecule formed in interstellar ices before subliming in star-forming regions like SgrB2(N), thus providing a critical entry point to prebiotic organic synthesis.