Context. Comets are considered to be remnants from the formation of the Solar System. ESA s Rosetta mission targeted comet 67P/Churyumov-Gerasimenko and was able to record high-quality data on its chemical composition and outgassing behaviour, including low abundances of N2 that are observed to be correlated with H2O and CO2 in approximately a 63:37 ratio. Aims. In this work, the thermal desorption behaviour of N2 in H2O:CO2 ices was studied in the laboratory to investigate the co-desorption behaviour of N2 within the two most abundant cometary ices in 67P and to derive desorbing fractions in different temperature regimes. Methods. H2O:CO2:N2 ices of various ratios were prepared in a gas mixing system and co-deposited at 15 K onto a copper sample holder. Sublimation of the ice was measured using temperature programmed desorption mass spectrometry. Quantitative values were derived for the fraction of N2 co-desorbing with CO2 and H2O respectively. To validate the results, H2O:CO2:13CO ices were prepared as well. Results. The experiments show that the co-desorption of N2 with CO2 in H2O:CO2:N2 ices depends on the bulk amount of CO2 present in the ice. The fraction of N2 trapped in H2O reduces as more N2 and CO2 are added to the mixture. CO behaves qualitatively similar to N2, but more CO is found to co-desorb with CO2. To reproduce the ratio of N2 desorbing with H2O over that of CO2 (N2(H2O)/N2(CO2)), our ice analogues need to contain =15% CO2, while 67P contains =7.5% CO2. Large fractions of N2 can be removed from the ice due to heating up to 70 K, but for ice that most closely resembles that of 67P, the loss fraction of pure phase N2 is expected to be =20%. Therefore, N2 is suggested to be a minor carrier of nitrogen in the comet.

Various Solar System objects are covered in layers of ice that are dominated by H ₂O, CH ₄, and N ₂ and in which complex chemical processes take place. In this work, the influence of composition and irradiation duration on the volatile irradiation products of mixed CH ₄:N ₂, CH ₄:H ₂O, and CH ₄:H ₂O:N ₂ ices after electron irradiation are studied. The ices were irradiated for 2 or 4 h with 5 keV electrons, followed by a temperature programmed desorption, where the desorption of the volatile irradiation products was observed. The formation of C ₂H _x and C ₃H _x is observed in all ices and for both irradiation times. For the ices containing H ₂O, molecules as large as tentatively identified C ₄H _x and C ₅H _x are observed to co-desorb with water, whereas for CH ₄:N ₂ a continuous desorption signal is observed instead of a sharp desorption peak. A decrease in signal intensity from the 2 to the 4 h irradiation is observed for most m/z signals in CH ₄:H ₂O and CH ₄:H ₂O:N ₂ ices, whereas the opposite is recorded for CH ₄:N ₂, where in general larger signal for longer irradiation duration is seen. The addition of nitrogen to the CH ₄:H ₂O ice did not lead to clear identification of different molecules, but instead to a decrease of the observed signal for complex molecules, suggesting that the addition of nitrogen to the CH ₄:H ₂O mixture primarily leads to a more effective incorporation of material in an organic residue. The analysis of the residue will be subject of future work to complement the findings in this study.

Aims. The ability of bulk ices (H₂O, CO₂) to trap volatiles has been well studied in any experimental sense, but largely ignored in protoplanetary disk and planet formation models as well as the interpretation of their observations. We demonstrate the influence of volatile trapping on C/O ratios in planet-forming environments. Methods. We created a simple model of CO, CO₂, and H₂O snowlines in protoplanetary disks and calculated the C/O ratio at different radii and temperatures. We included a trapping factor, which partially inhibits the release of volatiles (CO, CO₂) at their snowline and releases them instead, together with the bulk ice species (H₂O, CO₂). Our aim has been to assess its influence of trapping solid-state and gas phase C/O ratios throughout planet-forming environments. Results. Volatile trapping significantly affects C/O ratios in protoplanetary disks. Variations in the ratio are reduced and become more homogeneous throughout the disk when compared to models that do not include volatile trapping. Trapping reduces the proportion of volatiles in the gas and, as such, reduces the available carbon- and oxygen-bearing molecules for gaseous accretion to planetary atmospheres. Volatile trapping is expected to also affect the elemental hydrogen and nitrogen budgets. Conclusions. Volatile trapping is an overlooked, but important effect to consider when assessing the C/O ratios in protoplanetary disks and exoplanet atmospheres. Due to volatile trapping, exoplanets with stellar C/O have the possibility to be formed within the CO and CO₂ snowline.

Context. The ROSINA instrument on board the Rosetta spacecraft measured, among others, the outgassing of noble gases from comet 67P/Churyumov- Gerasimenko. The interpretation of this dataset and unravelling underlying desorption mechanisms requires detailed laboratory studies. Aims. We aim to improve our understanding of the desorption patterns, trapping, and fractionation of noble gases released from the H₂O:CO₂-dominated ice of comet 67P. Methods. In the laboratory, ice films of neon, argon, krypton, or xenon (Ne, Ar, Kr, and Xe) mixed in CO₂:H₂O were prepared at 15 K. Temperature-programmed desorption mass spectrometry is employed to analyse the desorption behaviour of the noble gases. Mass spectrometric ROSINA data of 67P were analysed to determine the fraction of argon associated with CO₂ and H₂O, respectively. Results. CO₂ has a significant effect on noble gas desorption behaviour, resulting in the co-release of noble gases with CO₂, decreasing the amount of noble gas trapped within water, shifting the pure phase noble gas peak desorption temperature to lower temperatures, and prolonging the trapping of neon. These effects are linked to competition for binding sites in the water ice and the formation of crystalline CO₂. Desorption energies of the pure phase noble gas release were determined and found to be higher than those previously reported in the literature. Enhancement of the Ar/Kr and Ar/Xe ratios are at best 40% and not significantly influenced by the addition of CO₂. Analysis of ROSINA mass spectrometric data shows that the fraction of argon associated with H₂O is 0.53 ± 0.30, which cannot be explained by our laboratory results. Conclusions. Multicomponent ice mixtures affect the desorption behaviour of volatiles compared to simple binary mixtures and experiments on realistic cometary ice analogues are vital to understanding comet outgassing.

Organic macromolecular matter is the dominant carrier of volatile elements such as carbon, nitrogen and noble gases in chondrites—the rocky building blocks from which Earth formed. How this macromolecular substance formed in space is unclear. Here we show that its formation could be associated with the presence of dust traps, which are prominent mechanisms for forming planetesimals in planet-forming disks. We demonstrate the existence of heavily irradiated zones in dust traps, where small frozen molecules that coat large quantities of microscopic dust grains could be rapidly converted into macromolecular matter by receiving radiation doses of up to several tens of electronvolts per molecule per year. This allows for the transformation of simple molecules into complex macromolecular matter within several decades. Up to roughly 4% of the total disk ice reservoir can be processed this way and subsequently incorporated into the protoplanetary disk midplane where planetesimals form. This finding shows that planetesimal formation and the production of organic macromolecular matter, which provides the essential elemental building blocks for life, might be linked.

Technological progress related to astronomical observatories such as the recently launched James Webb Space Telescope (JWST) allows searching for signs of life beyond our solar system, namely, in the form of unambiguous biosignature gases in exoplanetary atmospheres. The tentative assignment of a 1σ-2.4σ spectral feature observed with JWST in the atmosphere of exoplanet K2-18b to the biosignature gas dimethyl sulfide (DMS; sum formula C₂H₆S) raised hopes that, although controversial, a second genesis had been found. Terrestrial atmospheric DMS is exclusively stemming from marine biological activity, and no natural abiotic source has been identified—neither on Earth nor in space. Therefore, DMS is considered a robust biosignature. Since comets possess a pristine inventory of complex organic molecules of abiotic origin, we have searched high-resolution mass spectra collected at comet 67P/Churyumov-Gerasimenko, target of the European Space Agency’s Rosetta mission, for the signatures of DMS. Previous work reported the presence of a C₂H₆S signal when the comet was near its equinox, but distinction of DMS from its structural isomer ethanethiol remained elusive. Here we reassess these and evaluate additional data. Based on differences in the electron ionization-induced fragmentation pattern of the two isomers, we show that DMS is significantly better compatible with the observations. Deviations between expected and observed signal intensities for DMS are <1σ, while for ethanethiol they are 2σ-4σ. The local abundance of DMS relative to methanol deduced from these data is (0.13 ± 0.04)%. Our results provide the first evidence for the existence of an abiotic synthetic pathway to DMS in pristine cometary matter and hence motivate more detailed studies of the sulfur chemistry in such matter and its analogs. Future studies need to investigate whether or not the present inference of cometary DMS could provide an abiotic source of DMS in a planetary atmosphere.

Context. Many molecules observed in the interstellar medium are thought to result from the thermal desorption of ices. Parameters such as the desorption energy and pre-exponential frequency factor are essential in describing the desorption of molecules. Experimental determinations of these parameters are missing for many molecules, including those found in the interstellar medium. Aims. The objective of this work is to expand the number of molecules for which desorption parameters are available, by collecting and re-analysing experimental temperature programmed desorption data that are present in the literature. Methods. We used transition state theory (TST) in combination with the Redhead equation to determine the desorption parameters. Experimental data and molecular constants (e.g. mass, moment of inertia, etc.) were collected and given as input. Results. Using the Redhead-TST method, the desorption parameters for 133 molecules were determined. The Redhead-TST method is found to provide reliable results that agree well with desorption parameters determined on the basis of more rigorous experimental methods. The importance of using accurately determined pre-exponential frequency factors to simulate desorption profiles is highlighted here. The large amount of data allows us to look for trends, with the most important being the relationship log10(v) = 2.65ln(m) + 8.07, where ν is the pre-exponential frequency factor and m is the mass of the molecule. Conclusions. The data collected in this work allow for the thermal desorption of molecules to be modeled, with the aim of helping improve our understanding of changes in the chemical and elemental composition of interstellar environments.

European Space Agency's Rosetta spacecraft at comet 67P/Churyumov-Gerasimenko (67P) was the first mission that accompanied a comet over a substantial fraction of its orbit. On board was the Rosetta Orbiter Spectrometer for Ion and Neutral Analysis mass spectrometer suite to measure the local densities of the volatile species sublimating from the ices inside the comet's nucleus. Understanding the nature of these ices was a key goal of Rosetta. We analysed the primary cometary molecules at 67P, namely H ₂O and CO ₂, together with a suite of minor species for almost the entire mission. Our investigation reveals that the local abundances of highly volatile species, such as CH ₄ and CO, are reproduced by a linear combination of both H ₂O and CO ₂ densities. These findings bear similarities to laboratory-based temperature-programmed desorption experiments of amorphous ices and imply that highly volatile species are trapped in H ₂O and CO ₂ ices. Our results do not show the presence of ices dominated by these highly volatile molecules. Most likely, they were lost due to thermal processing of 67P's interior prior to its deflection to the inner solar system. Deviations in the proportions co-released with H ₂O and CO ₂ can only be observed before the inbound equinox, when the comet was still far from the sun and the abundance of highly volatile molecules associated with CO ₂ outgassing were lower. The corresponding CO ₂ is likely seasonal frost, which sublimated and lost its trapped highly volatile species before re-freezing during the previous apparition. CO, on the other hand, was elevated during the same time and requires further investigation.

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, C ₂H, 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 C ₂H 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 H ₂O and NH ₃ gas abundances are significantly boosted by ice sublimation. However, these models are inconsistent with the upper limits on the H ₂O 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 C ₂H 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 N ₂ and ≤ 0.6,

Context. Complex organic species are known to be abundant toward low- and high-mass protostars. No statistical study of these species toward a large sample of high-mass protostars with the Atacama Large Millimeter/submillimeter Array (ALMA) has been carried out so far. Aims. We aim to study six N-bearing species: methyl cyanide (CH3CN), isocyanic acid (HNCO), formamide (NH2CHO), ethyl cyanide (C2H5CN), vinyl cyanide (C2H3CN) and methylamine (CH3NH2) in a large sample of line-rich high-mass protostars. Methods. From the ALMA Evolutionary study of High Mass Protocluster Formation in the Galaxy survey, 37 of the most line-rich hot molecular cores with ∼ 1"angular resolution are selected. Next, we fit their spectra and find column densities and excitation temperatures of the N-bearing species mentioned above, in addition to methanol (CH3OH) to be used as a reference species. Finally, we compare our column densities with those in other low- and high-mass protostars. Results. CH3OH, CH3CN and HNCO are detected in all sources in our sample, whereas C2H3CN and CH3NH2 are (tentatively) detected in ∼ 78 and ∼ 32% of the sources. We find three groups of species when comparing their excitation temperatures: hot (NH2CHO; Tex3 250 K), warm (C2H3CN, HN13CO and CH313CN; 100 K 2 Tex2 250 K) and cold species (CH3OH and CH3NH2; Tex2 100 K). This temperature segregation reflects the trend seen in the sublimation temperature of these molecules and validates the idea that complex organic emission shows an onion-like structure around protostars. Moreover, the molecules studied here show constant column density ratios across low- and high-mass protostars with scatter less than a factor ∼ 3 around the mean. Conclusions. The constant column density ratios point to a common formation environment of complex organics or their precursors, most likely in the pre-stellar ices. The scatter around the mean of the ratios, although small, varies depending on the species considered. This spread can either have a physical origin (source structure, line or dust optical depth) or a chemical one. Formamide is most prone to the physical effects as it is tracing the closest regions to the protostars, whereas such effects are small for other species. Assuming that all molecules form in the pre-stellar ices, the scatter variations could be explained by differences in lifetimes or physical conditions of the pre-stellar clouds. If the pre-stellar lifetimes are the main factor, they should be similar for low- and high-mass protostars (within factors ∼ 2- 3).

This work aims to constrain the abundances of interstellar amides, by searching for this group of prebiotic molecules in the intermediate-mass protostar Serpens SMM1-a. ALMA observations are conducted toward Serpens SMM1. A spectrum is extracted toward the SMM1-a position and analyzed with the CASSIS line analysis software for the presence of characteristic rotational lines of a number of amides and other molecules. NH ₂CHO, NH ₂CHO ν ₁₂= 1, NH ₂ ¹³CHO, CH ₃C(O)NH ₂ν = 0, 1, CH ₂DOH, CH ₃CHO, and CH ₃C(O)CH ₃are securely detected, while trans-NHDCHO, NH ₂CDO, CH ₃NHCHO ν = 0, 1, CH ₃COOH, and HOCH ₂CHO are tentatively identified. The results of this work are compared with detections presented in the literature. A uniform CH ₃C(O)NH ₂/NH ₂CHO ratio is found for a group of interstellar sources with vast physical differences. A similar ratio is seen for CH ₃NHCHO, based on a smaller data sample. The D/H ratio of NH ₂CHO is about 1-3% and is close to values found in the low-mass source IRAS 16293-2422B. The formation of CH ₃C(O)NH ₂and NH ₂CHO is likely linked. Formation of these molecules on grain surfaces during the dark cloud stage is a likely scenario. The high D/H ratio of NH ₂CHO is also seen as an indication that these molecules are formed on icy dust grains. As a direct consequence, amides are expected to be present in the most pristine material from which planetary systems form, thus providing a reservoir of prebiotic material.

Spectroscopic instruments were a part of payloads on orbiter and lander missions and delivered vast data sets to explore minerals, elements and molecules on air-less rocky planets, asteroids and comets on global and local scales. To answer current space science questions, the chemical composition of planetary rocks and soils at grain scale is required, as well as measurements of element (isotope) concentrations down to the part per million or lower. Only mass spectrometric methods equipped with laser sampling ion sources can deliver the necessary information. Laser sampling techniques can reduce the dimensions of the investigated sample material down to micrometre scale, allowing for the composition analysis of grain-sized objects or thin mineral layers with sufficiently high spatial resolution, such that important geological processes can be recognised and studied as they progressed in time. We describe the performance characteristics, when applied to meteorite and geological samples, of a miniaturised laser ablation/ionisation mass spectrometer (named LMS) system that has been developed in our group. The main advantages of the LMS instrument over competing techniques are illustrated by examples of high spatial (lateral and vertical) resolution studies in different meteorites, terrestrial minerals and fossil-like structures in ancient rocks for most elements of geochemical interest. Top-level parameters, such as dimension, weight, and power consumption of a possible flight design of the LMS system are presented as well.

Exploring how life is distributed in the universe is an extraordinary interdisciplinary challenge, but increasingly subject to testable hypotheses. Biology has emerged and flourished on at least one planet, and that renders the search for life elsewhere a scientific question. We cannot hope to travel to exoplanets in pursuit of other life even if we identify convincing biosignatures, but we do have direct access to planets and moons in our solar system. It is therefore a matter of deep astrobiological interest to study their histories and environments, whether or not they harbor life, and better understand the constraints that delimit the emergence and persistence of biology in any context. In this perspective, we argue that targeted chemistry- and biology-inspired experiments are informative to the development of instruments for space missions, and essential for interpreting the data they generate. This approach is especially useful for studying Venus because if it were an exoplanet we would categorize it as Earth-like based on its mass and orbital distance, but its atmosphere and surface are decidedly not Earth-like. Here, we present a general justification for exploring the solar system from an astrobiological perspective, even destinations that may not harbor life. We introduce the extreme environments of Venus, and argue that rigorous and observation-driven experiments can guide instrument development for imminent missions to the Venusian clouds. We highlight several specific examples, including the study of organic chemistry under extreme conditions, and harnessing the fluorescent properties of molecules to make a variety of otherwise challenging measurements.

Polycyclic aromatic hydrocarbons (PAHs) are found on various planetary surfaces in the solar system. They are proposed to play a role in the emergence of life, as molecules that are important for biological processes could be derived from them. In this work, four PAHs (pyrene, perylene, anthracene, and coronene) were measured using the ORganics Information Gathering INstrument system (ORIGIN), a lightweight laser desorption ionization-mass spectrometer designed for space exploration missions. In this contribution, we demonstrate the current measurement capabilities of ORIGIN in detecting PAHs at different concentrations and applied laser pulse energies. Furthermore, we show that chemical processing of the PAHs during measurement is limited and that the parent mass can be detected in the majority of cases. The instrument achieves a 3σ detection limit in the order of femtomol mm ⁻² for all four PAHs, with the possibility of further increasing this sensitivity. This work illustrates the potential of ORIGIN as an instrument for the detection of molecules important for the emergence or presence of life, especially when viewed in combination with previous results by the instrument, such as the identification of amino acids. ORIGIN could be used on a lander or rover platform for future in situ missions to targets in the solar system, such as the icy moons of Jupiter or Saturn.

In the search for extraterrestrial life, biosignatures (e.g., organic molecules) play an important role, of which lipids are one considerable class. If detected, these molecules can be strong indicators of the presence of life, past or present, as they are ubiquitous in life on Earth. However, their detection is challenging, depending on, e.g., instrument performance, as well as the selected site. In this contribution, we demonstrate that, using laser desorption ionization mass spectrometry, detection of lipids is feasible. Using our space prototype instrument designed and built in-house, six representative lipids were successfully detected: cholecalciferol, phylloquinone, menadione, 17α-ethynylestradiol, α-tocopherol, and retinol, both as pure substances and as mixtures additionally containing amino acids or polycyclic aromatic hydrocarbons. Observed limits of detection for lipids already meet the requirements stated in the Enceladus Orbilander mission concept. The current performance of our LDI-MS system allows for the simultaneous identification of lipids, amino acids, and polycyclic aromatic hydrocarbons, using a single instrument. We therefore believe that the LDI-MS system is a promising candidate for future space exploration missions devoted to life detection.

Recent and past observations of chemical and physical peculiarities in the atmosphere of Venus have renewed speculations about the existence of life in its clouds. To find signs of Venusian life, a dedicated astrobiological space exploration mission is required, and for this reason the Venus Life Finder mission is currently being prepared. A Venus Life Finder mission will require dedicated and specialized instruments to hunt for biosignatures and habitability indicators. In this contribution, we present the ORIGIN space instrument, a laser desorption/laser ablation ionization mass spectrometer. This instrument is designed to detect large, non-volatile molecules, specifically biomolecules such as amino acids and lipids. At the same time, it can also be used in ablation mode for elemental composition analysis. Recent studies with this space prototype instrument of amino acids, polycyclic aromatic hydrocarbons, lipids, salts, metals, sulphur isotopes, and microbial elemental composition are discussed in the context of studies of biosignatures and habitability indicators in Venus’s atmosphere. The implementation of the ORIGIN instrument into a Venus Life Finder mission is discussed, emphasizing the low weight and low power consumption of the instrument. An instrument design and sample handling system are presented that make optimal use of the capabilities of this instrument. ORIGIN is a highly versatile instrument with proven capabilities to investigate and potentially resolve many of the outstanding questions about the atmosphere of Venus and the presence of life in its clouds.

Context. Recent observations of protoplanetary disks suggest that they are depleted in gas-phase CO up to a factor of 100 with respect to predictions from physical-chemical (or thermo-chemical) models. It has been posed that gas-phase CO is chemically consumed and converted into less volatile species through gas-grain processes. Observations of interstellar ices reveal a CO2 component in a polar (H2O) ice matrix, suggesting potential co-formation or co-evolution. Aims. The aim of this work is to experimentally verify the interaction of gas-phase CO with solid-state OH radicals on the surface of water ice above the sublimation temperature of CO. Methods. Amorphous solid water (ASW) is deposited in an ultra-high vacuum (UHV) setup at 15 K and irradiated with vacuum-UV (VUV) photons (140-170 nm, produced with a microwave-discharge hydrogen-flow lamp) to dissociate H2O and create OH radicals. Gas-phase CO is simultaneously admitted and only adsorbs with a short residence time on the ASW. Formed products in the solid state are studied in the infrared through Fourier transform infrared spectroscopy and once released into the gas phase with quadrupole mass spectrometry. Results. Our experiments show that gas-phase CO is converted into CO2 when interacting with ASW that is VUV irradiated with a conversion efficiency of 7-27%. Between 40 and 90 K, CO2 production is constant, above 90 K, CO2 production is reduced in favor of O2 production. In the temperature range of 40-60 K, the CO2 remains in the solid state, while at temperatures 70 K the majority of the formed CO2 is immediately released into the gas phase. Conclusions. We conclude that gas-phase CO reacts with OH radicals, created on the surface of ASW with VUV irradiation, above its canonical sublimation temperature. The diffusion during the short, but nonzero, residence times of CO on the surface of ASW suggests that a Langmuir-Hinshelwood type reaction is involved. This gas-phase CO and solid-state OH radical interaction could explain (part of) the observed presence of CO2 embedded in water-rich ices when it occurs during the build up of the H2O ice mantle. It may also contribute to the observed lack of gas-phase CO in planet-forming disks, as previously suggested. It should be noted though that our experiments indicate a lower water ice dissociation efficiency than originally adopted in model descriptions of planet-forming disks and molecular clouds. Incorporation of the reduced water ice dissociation and increased binding energy of CO on a water ice surfaces in physical-chemical models would allow investigation of this gas-grain interaction to its full extend.

Context. The chemical inventory of planets is determined by the physical and chemical processes that govern the early phases of star formation. Nitrogen-bearing species are of interest as many provide crucial precursors in the formation of life-related matter. Aims. The aim is to investigate nitrogen-bearing complex organic molecules towards two deeply embedded Class 0 low-mass protostars (Perseus B1-c and Serpens S68N) at millimetre wavelengths with the Atacama Large Millimeter/submillimeter Array (ALMA). Next, the results of the detected nitrogen-bearing species are compared with those of oxygen-bearing species for the same and other sources. The similarities and differences are used as further input to investigate the underlying formation pathways. Methods. ALMA observations of B1-c and S68N in Band 6 (~1 mm) and Band 5 (~2 mm) are studied at ~0.5′′ resolution, complemented by Band 3 (~3 mm) data in a ~2.5′′ beam. The spectra are analysed for nitrogen-bearing species using the CASSIS spectral analysis tool, and the column densities and excitation temperatures are determined. A toy model is developed to investigate the effect of source structure on the molecular emission. Results. Formamide (NH2CHO), ethyl cyanide (C2H5CN), isocyanic acid (HNCO, HN13CO, DNCO), and methyl cyanide (CH3CN, CH2DCN, and CHD2CN) are identified towards the investigated sources. Their abundances relative to CH3OH and HNCO are similar for the two sources, with column densities that are typically an order of magnitude lower than those of oxygen-bearing species. The largest variations, of an order of magnitude, are seen for NH2CHO abundance ratios with respect to HNCO and CH3OH and do not correlate with the protostellar luminosity. In addition, within uncertainties, the nitrogen-bearing species have similar excitation temperatures to those of oxygen-bearing species (~100-300 K). The measured excitation temperatures are larger than the sublimation temperatures for the respective species. Conclusions. The similarity of most abundances with respect to HNCO for the investigated sources, including those of CH2DCN and CHD2CN, hints at a shared chemical history, especially the high D-to-H ratio in cold regions prior to star formation. However, some of the variations in abundances may reflect the sensitivity of the chemistry to local conditions such as temperature (e.g. NH2CHO), while others may arise from differences in the emitting areas of the molecules linked to their different binding energies in the ice. The excitation temperatures likely reflect the mass-weighted kinetic temperature of a gas that follows a power law structure. The two sources discussed in this work add to the small number of sources that have been subjected to such a detailed chemical analysis on Solar System scales. Future data from the James Webb Space Telescope will allow a direct comparison between the ice and gas abundances of both smaller and larger nitrogen-bearing species.