Identification of solid N

Context. Only six molecules containing an N-O bond are detected in the gaseous phase of the interstellar medium. One of them is nitrous oxide (N2O), which was unsuccessfully searched for in solid form since the launch of the Infrared Space Observatory (ISO) mission. The observational capabilities of the James Webb Space Telescope (JWST) present the possibility of identifying solid interstellar N2O. Aims. We aim to identify nitrous oxide in open JWST spectra of interstellar ices toward a sample of Class 0, 0/I, and flat protostars using the relevant laboratory mixtures of N2O-bearing interstellar ice analogs. Methods. A set of laboratory infrared transmission spectra was obtained for the following mixtures: N2O:CO2 = 1:20, N2O:CO = 1:20, N2O:N2 = 1:20, N2O:CO2:CO = 1:15:5, and N2O:CO2:N2 = 1:15:13 at 10–23 K. A search for N2O in JWST NIRSpec spectra toward 50 protostars was performed by fitting the 4.44–4.47 μm (2250–2235 cm−1) NN-stretch absorption band with new laboratory mixtures of N2O-bearing ices. Results. We claim the first secure identification of N2O in 16 protostars. The fitting results show that N2O is formed predominantly within the apolar layer of the ice mantles, which are rich in CO, CO2, and N2. The abundance of solid N2O is estimated at 0.2–2.1% relative to solid CO. We present the band strengths for N2O in the mixtures corresponding to the apolar layer. We also report the identification of the C-N stretch band at 4.42 μm (2260 cm−1), which we tentatively assign to HNCO, the simplest C-N bond carrier.