The complex organic molecules (COMs) detected in star-forming regions are the precursors of the prebiotic molecules that can lead to the emergence of life. By studying COMs in more evolved protoplanetary disks we can gain a better understanding of how they are incorporated into planets. This paper presents ALMA band 7 observations of the dust and ice trap in the protoplanetary disk around Oph IRS 48. We report the first detection of dimethyl ether (CH3OCH3) in a planet-forming disk and a tentative detection of methyl formate (CH3OCHO). We determined column densities for the detected molecules and upper limits on non-detected species using the CASSIS spectral analysis tool. The inferred column densities of CH3OCH3 and CH3OCHO with respect to methanol (CH3OH) are of order unity, indicating unusually high abundances of these species compared to other environments. Alternatively, the 12CH3OH emission is optically thick and beam diluted, implying a higher CH3OH column density and a smaller emitting area than originally thought. The presence of these complex molecules can be explained by thermal ice sublimation, where the dust cavity edge is heated by irradiation and the full volatile ice content is observable in the gas phase. This work confirms the presence of oxygen-bearing molecules more complex than CH3OH in protoplanetary disks for the first time. It also shows that it is indeed possible to trace the full interstellar journey of COMs across the different evolutionary stages of star, disk, and planet formation.

Context. Most well-resolved disks observed with the Atacama Large Millimeter/submillimeter Array (ALMA) show signs of dust traps. These dust traps set the chemical composition of the planet-forming material in these disks, as the dust grains with their icy mantles are trapped at specific radii and could deplete the gas and dust at smaller radii of volatiles. Aims. In this work, we analyse the first detection of nitric oxide (NO) in a protoplanetary disk. We aim to constrain the nitrogen chemistry and the gas-phase C/O ratio in the highly asymmetric dust trap in the Oph-IRS 48 disk. Methods. We used ALMA observations of NO, CN, C2H, and related molecules in the Oph-IRS 48 disk. We modeled the effect of the increased dust-to-gas ratio in the dust trap on the physical and chemical structure using a dedicated nitrogen chemistry network in the thermochemical code DALI. Furthermore, we explored how ice sublimation contributes to the observed emission lines. Finally, we used the model to put constraints on the nitrogen-bearing ices. Results. Nitric oxide (NO) is only observed at the location of the dust trap, but CN and C2H are not detected in the Oph-IRS 48 disk. This results in an CN/NO column density ratio of <0.05 and thus a low C/O ratio at the location of the dust trap. Models show that the dust trap cools the disk midplane down to ~30 K, just above the NO sublimation temperature of ~25 K. The main gas-phase formation pathways to NO though OH and NH in the fiducial model predict NO emission that is an order of magnitude lower than what has been observed. The gaseous NO column density can be increased by factors ranging from 2.8 to 10 when the H2O and NH3 gas abundances are significantly boosted by ice sublimation. However, these models are inconsistent with the upper limits on the H2O and OH column densities derived from Herschel PACS observations and the upper limit on CN derived from ALMA observations. As the models require an additional source of NO to explain its detection, the NO seen in the observations is likely the photodissociation product of a larger molecule sublimating from the ices. The non-detection of CN provides a tighter constraint on the disk C/O ratio than the C2H upper limit. Conclusions. We propose that the NO emission in the Oph-IRS 48 disk is closely related to the nitrogen-bearing ices sublimating in the dust trap. The non-detection of CN constrains the C/O ratio both inside and outside the dust trap to be <1 if all nitrogen initially starts as N2 and ≤ 0.6, consistent with the Solar value, if (at least part of) the nitrogen initially starts as N or NH3.

Context. In the near future, high spatial and spectral infrared (IR) data of star-forming regions obtained by the James Webb Space Telescope (JWST) may reveal new solid-state features of various species, including more intriguing classes of chemical compounds. The identification of Complex organic molecules (COMs) in the upcoming data will only be possible when laboratory IR ice spectra of these species under astronomically relevant conditions are available for comparison. For this purpose, systematic series of laboratory measurements are performed, providing high-resolution IR spectra of COMs. Here, spectra of pure methylamine (CH3NH2) and methylamine-containing ices are discussed. Aims. The work is aimed at characterizing the mid-IR (500 -4000 cm −1 , 20 -2.5 µm) spectra of methylamine in pure and mixed ices to provide accurate spectroscopic data of vibrational bands that are most suited to trace this species in interstellar ices. Methods. Fourier transform infrared (FTIR) spectroscopy is used to record spectra of CH3NH2 in the pure form and mixed with H2O, CH4, and NH3, for temperatures ranging from 15 to 160 K. The IR spectra in combination with HeNe laser (632.8 nm) interference data of pure CH3NH2 ice was used to derive the IR band strengths of methylamine in pure and mixed ices. Results. The refractive index of amorphous methylamine ice at 15 K was determined as being 1.30 ± 0.01. Accurate spectroscopic information and band strength values are systematically presented for a large set of methylamine-containing ices and different temperatures. Selected bands are characterized and their use as methylamine tracers is discussed. The selected bands include the following: the CH3 antisymmetric stretch band at 2881.3 cm −1 (3.471 µm), the CH3 symmetric stretch band at 2791.9 cm −1 (3.582 µm), the CH3 antisymmetric deformation bands, at 1455.0 and 1478.6 cm −1 (6.873 µm and 6.761 µm), the CH3 symmetric deformation band at 1420.3 cm −1 (7.042 µm), and the CH3 rock at 1159.2 cm −1 (8.621 µm). Using the laboratory data recorded in this work and ground-based spectra of ices toward YSOs (Young Stellar Objects), upper-limits for the methylamine ice abundances are derived. In some of these YSOs, the methylamine abundance is less than 4% relative to H2O.