Identification of Glycolaldehyde Enol (HOHC═CHOH) in Interstellar Analogue Ices

Glycolaldehyde is considered the entry point in the aqueous prebiotic formose (Butlerow) reaction although it mainly exists in its unreactive hydrated form in aqueous solution. The characterization of the more reactive nucleophilic enol form under interstellar conditions has remained elusive to date. Here we report on the identification of glycolaldehyde enol (1,2-ethenediol, HOHC═CHOH) in low temperature methanol-bearing ices at temperatures as low as 5 K. Exploiting isotope labeling and isomer-selective photoionization coupled with reflectron time-of-flight mass spectrometry, our results unravel distinct reaction pathways to 1,2-ethenediol, thus demonstrating the kinetic stability, availability for prebiotic sugar formation, and potential detectability in deep space.