Interstellar Molecules Research Articles

Multifaceted potential applicability of hydrotalcite-type anionic clays from green chemistry to environmental sustainability

Hydrotalcite-like anionic clays (HTs) also known as Layered double hydroxides (LDHs) have been developed as multifunctional materials in numerous applications related to catalysis, adsorption, and ion-exchange processes. These materials constitute an important class of ionic lamellar solid clays of Brucite-like structure which comprise of consecutive layers of divalent and trivalent metal cations with charge balancing anions and water molecules in interlayer space. These materials have received increasing attention in research due to their interesting properties namely layered structure, ease of preparation, flexible tunability, ability to intercalate different types of anions, electronic properties, high thermal stability, high biocompatibility, and easy biodegradation. Moreover, HTs/LDHs have unique tailorable and tuneable characteristics such as both acidic and basic sites, anion exchange capability, surface area, basal spacing, memory effect, and also exhibit high exchange capacities, which makes them versatile materials for a wide range of applications and extended their horizons to diverse areas of science and technology. This study enlightens the various rational researches related to the synthetic methods and features focusing on synthesis and/or fabrication with other hybrids and their applications. The diverse applications (namely catalyst, adsorbent to toxic chemicals, agrochemicals management, non-toxic flame retardants, and recycling of plastics) of these multifunctional materials related to a clean and sustainable environment were also summarized.

Microneedle Array Technique for the Longitudinal Extraction of Interstitial Fluid without Hair Removal.

Interstitial fluid (ISF) bathes the cells and tissues and is in constant exchange with blood. As an exchange medium for waste, nutrients, exosomes, and signaling molecules, ISF is recognized as a plentiful source of biomolecules. Many basic and pre-clinical small animal studies could benefit from an inexpensive and efficient technique that allows for the in vivo extraction of ISF for the subsequent quantification of molecules in the interstitial space. We have previously reported on a minimally invasive technique for the extraction of ISF using a 3D-printed microneedle array (MA) platform for comprehensive biomedical applications. Previously, hairless animal models were utilized, and euthanasia was performed immediately following the procedure. Here, we demonstrate the technique in Sprague Dawley rats, without the need for hair removal, over multiple extractions and weeks. As an example of this technique, we report simultaneous quantification of the heavy metals Copper (Cu), Lead (Pb), Lithium (Li), and Nickel (Ni) within the ISF, compared with whole blood. These results demonstrate the MA technique applicability to a broader range of species and studies and the reuse of animals, leading to a reduction in number of animals needed to successfully complete ISF extraction experiments.

SOLIS

Context.Deuteration is a precious tool for investigating the origin and formation routes of interstellar complex organic molecules in the different stages of the star formation process. Methyl cyanide (CH3CN) is one of the most abundant interstellar complex organic molecules (iCOMs); it is of particular interest because it is among the very few iCOMs detected not only around protostars but also in protoplanetary disks. However, its formation pathways are not well known and only a few measurements of its deuterated isotopologue (CH2DCN) have been made to date.Aims.We studied the line emission from CH3CN and its deuterated isotopologue CH2DCN towards the prototypical Class I object SVS13-A, where the deuteration of a large number of species has already been reported. Our goal is to measure the CH3CN deuteration in a Class I protostar, for the first time, in order to constrain the CH3CN formation pathways and the chemical evolution from the early prestellar core and Class 0 to the evolved Class I stages.Methods.We imaged CH2DCN towards SVS13-A using the IRAM NOEMA interferometer at 3mm in the context of the Large Program SOLIS (with a spatial resolution of 1″.8 × 1″.2). The NOEMA images were complemented by the CH3CN and CH2DCN spectra collected by the IRAM-30m Large Program ASAI, which provided an unbiased spectral survey at 3 mm, 2 mm, and 1.3 mm. The observed line emission was analysed using local thermodynamic equilibrium (LTE) and non-LTE large velocity gradient (LVG) approaches.Results.The NOEMA/SOLIS images of CH2DCN show that this species emits in an unresolved area centred towards the SVS13-A continuum emission peak, suggesting that methyl cyanide and its isotopologues are associated with the hot corino of SVS13-A, previously imaged via other iCOMs. In addition, we detected 41 and 11 ASAI transitions of CH3CN and CH2DCN, respectively, which cover upper level energies (Eup) from 13 to 442 K and from 18 K to 200 K. The non-LTE LVG analysis of the CH3CN lines points to a kinetic temperature of (140 ± 20) K, a gas density nH2≥ 107 cm−3, and an emitting size of ~0″.3, in agreement with the hypothesis that CH3CN lines are emitted in the SVS13-A hot corino. The derived [CH2DCN]/[CH3CN] ratio is ~9%. This value is consistent with those measured towards prestellar cores and a factor 2–3 higher than those measured in Class 0 protostars.Conclusions.Contrarily to what expected for other molecular species, the CH3CN deuteration does not show a decrease in SVS13-A with respect to measurements in younger prestellar cores and Class 0 protostars. Finally, we discuss why our new results suggest that CH3CN was likely synthesised via gas-phase reactions and frozen onto the dust grain mantles during the cold prestellar phase.

Interstellar detection and chemical modeling of iso-propanol and its normal isomer

Context.The detection of a branched alkyl molecule in the high-mass star forming protocluster Sagittarius (Sgr) B2(N) permitted by the advent of the Atacama Large Millimeter/submillimeter Array (ALMA) revealed a new dimension of interstellar chemistry. Astrochemical simulations subsequently predicted that beyond a certain degree of molecular complexity, branched molecules could even dominate over their straight-chain isomers.Aims.More generally, we aim to probe further the presence in the interstellar medium of complex organic molecules with the capacity to exhibit both a normal and iso form, via the attachment of a functional group to either a primary or secondary carbon atom. Methods. We used the imaging spectral line survey ReMoCA performed with ALMA at high angular resolution and the results of a recent spectroscopic study of propanol to search for the iso and normal isomers of this molecule in the hot molecular core Sgr B2(N2). We analyzed the interferometric spectra under the assumption of local thermodynamical equilibrium. We expanded the network of the astrochemical model MAGICKAL to explore the formation routes of propanol and put the observational results in a broader astrochemical context.Results.We report the first interstellar detection of iso-propanol, ¿-C3H7OH, toward a position of Sgr B2(N2) that shows narrow linewidths. We also report the first secure detection of the normal isomer of propanol, n-C3H7OH, in a hot core. Iso-propanol is found to be nearly as abundant as normal-propanol, with an abundance ratio of 0.6 which is similar to the ratio of 0.4 that we obtained previously for iso- and normal-propyl cyanide in Sgr B2(N2) at lower angular resolution with our previous ALMA survey, EMoCA. The observational results are in good agreement with the outcomes of our astrochemical models, which indicate that the OH-radical addition to propylene in dust-grain ice mantles, driven by water photodissociation, can produce appropriate quantities of normal- and iso-propanol. The normal-to-iso ratio in Sgr B2(N2) may be a direct inheritance of the branching ratio of this reaction process.Conclusions.The detection of normal- and iso-propanol and their ratio indicate that the modest preference for the normal form of propyl cyanide determined previously may be a more general feature among similarly sized interstellar molecules. Detecting other pairs of interstellar organic molecules with a functional group attached either to a primary or secondary carbon may help in pinning down the processes that dominate in setting their normal-to-iso ratios. Butanol and its isomers would be the next obvious candidates in the alcohol family, but their detection in hot cores will be challenging.

Quantification of molecular aromaticity as a predictive factor of astrophysical significance

Context. This study reports the index of aromaticity calculated by numerical integration of the magnetically-induced current density for cyclic hydrocarbon molecules both known to exist in astrophysical media as well as those proposed to exist. Aims. This study promotes the ring current strength (RCS) value for quantifying aromaticity as a means of predicting astrophysical detectability. Methods. Density functional theory (DFT) calculations at the B3LYP/aug-cc-pVTZ level provide optimized structures and the wave-functions needed to provide the RCS values for the molecules analyzed. Results. The known interstellar molecules examined c-C3H2, c-(O)C3H2, c-C3HC2H, o-benzyne, benzonitrile, 1-cyano and 2-cyanonaphthalene all have RCS values of 9.9 nA T−1 (nanoampere per Tesla) or above. The known antiaromatic species have RCS values of less than 0.0 nA T−1 as expected. Several proposed interstellar molecules likely will not persist if they form due to low RCS values including c-(C)C3H2. Other species such as p-benzyne and c-HCNN+ have high RCS values of 19.9 nAT−1 and 14.4nAT−1, respectively. Conclusions. Cyclic hydrocarbons previously observed in astrophysical media have high RCS values. Those with low or negative RCS values have yet to be observed implying that such a metric can indicate astrophysical significance.

Laboratory Measurement of Millimeter-wave Transitions of 13CH2DOH for Astronomical Use

Methanol (CH3OH) is an abundant interstellar species and is known to be an important precursor of various interstellar complex organic molecules. Among the methanol isotopologues, CH2DOH is one of the most abundant isotopologues and it is often used to study the deuterium fractionation of CH3OH in interstellar medium. However, the emission lines of CH2DOH can sometimes be optically thick, making the derivation of its abundance unreliable. Therefore, observations of its presumably optically thin 13C substituted species, 13CH2DOH, are essential to overcome this issue. In this study, the rotational transitions of 13CH2DOH have been measured in the millimeter-wave region from 216 GHz to 264 GHz with an emission-type millimeter- and submillimeter-wave spectrometer by using a deuterium and 13C enriched sample. The frequency accuracy of measured 13CH2DOH is less than a few kHz, and the relative line intensity error is less than 10% in most of the frequency range by taking advantage of the wide simultaneous frequency-coverage of the emission-type spectrometer. These results offer a good opportunity to detect 13CH2DOH in space, which will allow us to study the deuterium fractionation of CH3OH in various sources through accurate determination of the CH2DOH abundance.

Modelling the Radical Chemistry on Ice Surfaces: An Integrated Quantum Chemical and Experimental Approach

Heterogeneous radical processes on ice surfaces play a vital role in the formation of building blocks of the biologically relevant molecules in space. Therefore, quantitative mechanistic details of the radical binding and radical reactions on ices are crucial in rationalizing the chemical evolution in the Universe. The radical chemistry on ice surfaces was explored at low temperatures by combining quantum chemical calculations and laboratory experiments. A range of binding energies was observed for OH, HCO, CH3, and CH3O radicals binding on ices. Computed reaction paths of the radical reactions on ices, OCS + H and PH3 + D, explained the experimentally observed products. In both radical reactions, quantum tunnelling plays a key role in achieving the reactions at low temperatures. Our findings give quantitative insights into radical chemistry on ice surfaces in interstellar space and the planetary atmospheres.

Effect of Loading on the Water Stability of the Metal-Organic Framework DMOF-1 [Zn(bdc)(dabco)0.5

In this work, the degradation of the metal-organic framework (MOF) DMOF-1 as a function of water adsorption was investigated. As the quantity of water vapor adsorbed by DMOF-1 increases, degradation of the MOF from hydrolysis accelerates. Degradation was attributed to clustering of water molecules in the void space of DMOF-1, as seen in NVT Monte Carlo simulations. Our molecular simulations strongly suggest that degradation of DMOF-1 by water is driven by water adsorption at defect sites in the MOF. Interestingly, it was observed that DMOF-1 can remain stable if it adsorbs less water than the 1 mmol/g necessary to initiate degradation within the framework. Even though the rate of hydrolysis increases at higher temperatures, the degradation threshold for DMOF-1 remains 1 mmol/g regardless of temperature. This suggests that at sufficiently elevated temperatures (above ∼50 °C) DMOF-1 is stable toward water vapor at all relative humidities.

Quantum alchemy beyond singlets: Bonding in diatomic molecules with hydrogen.

Bonding energies play an essential role in describing the relative stability of molecules in chemical space. Therefore, methods employed to search chemical space need to capture the bonding behavior for a wide range of molecules, including radicals. In this work, we investigate the ability of quantum alchemy to capture the bonding behavior of hypothetical chemical compounds, specifically diatomic molecules involving hydrogen with various electronic structures. We evaluate equilibrium bond lengths, ionization energies, and electron affinities of these fundamental systems. We compare and contrast how well manual quantum alchemy calculations, i.e., quantum mechanics calculations in which the nuclear charge is altered, and quantum alchemy approximations using a Taylor series expansion can predict these molecular properties. Our results suggest that while manual quantum alchemy calculations outperform Taylor series approximations, truncations of Taylor series approximations after the second order provide the most accurate Taylor series predictions. Furthermore, these results suggest that trends in quantum alchemy predictions are generally dependent on the predicted property (i.e., equilibrium bond length, ionization energy, or electron affinity). Taken together, this work provides insight into how quantum alchemy predictions using a Taylor series expansion may be applied to future studies of non-singlet systems as well as the challenges that remain open for predicting the bonding behavior of such systems.

Computer Generated Realistic Interstellar Icy Grain Models: Physicochemical Properties and Interaction with NH3.

Interstellar grains are composed by a rocky core (usually amorphous silicates) covered by an icy mantle, the most abundant molecule being H2O followed by CO, CO2, NH3, and also radicals in minor quantities. In dense molecular clouds, gas-phase chemical species freeze onto the grain surface, making it an important reservoir of molecular diversity/complexity whose evolution leads to interstellar complex organic molecules (iCOMs). Many different models of water clusters have appeared in the literature, but without a systematic study on the properties of the grain (such as the H-bonds features, the oxygen radial distribution function, the dangling species present on the mantle surface, the surface electrostatic potential, etc.). In this work, we present a computer procedure (ACO-FROST) grounded on the newly developed semiempirical GFN2 tight-binding quantum mechanical method and the GFN-FF force field method to build-up structures of amorphous ice of large size. These methods show a very favorable accuracy/cost ratio as they are ideally designed to take noncovalent interactions into account. ACO-FROST program can be tuned to build grains of different composition mimicking dirty icy grains. These icy grain models allow studying the adsorption features (structure, binding energy, vibrational frequencies, etc.) of relevant species on a large variety of adsorption sites so to obtain a statistically meaningful distribution of the physicochemical properties of interest to be transferred in numerical models. As a test case, we computed the binding energy of ammonia adsorbed at the different sites of the icy grain surface, showing a broad distribution not easily accounted for by other more size limited icy grain models. Our method is also the base for further refinements, adopting the present grain in a more rigorous QM:MM treatment, capable of giving binding energies within the chemical accuracy.

POI-3DGCN: Predicting odor intensity of monomer flavors based on three-dimensionally embedded graph convolutional network

The relationship between spatial information of molecular topology and odor characteristics has received increasing attention from the academic community. Odor intensity (OI) prediction, as one of the most important topics in the olfactory systems (OS), has been thoroughly investigated in the past. Nonetheless, traditional methods have certain limitations as they usually require high-precision instruments and are time-consuming in collecting OI datasets. Here, we created a novel and efficient framework (POI-3DGCN) for OI prediction based on a three-dimensional graph convolutional network (3DGCN) model to overcome these challenges. Compared with other advanced models (RF, SVM, MLP, LSTM and GAT), the 3DGCN model exhibits significantly higher performance on the task of predicting OI. We confirmed that global pooling (aggregation), especially set2set, improves the predicted OI performance on monomer flavor datasets with sparser graph structures. More significantly, we found that the rotations of odor molecules in 3D space have the same topology, except for their 3D orientation, and the 3DGCN model predicts OI with has rotation equivariance, which also reflects the good robustness of this model. Consequently, the proposed POI-3DGCN model is likely to be considered reliable for evaluating the OI of monomer flavors, which lays a good foundation in the implementation of three-dimensionality to the field of deep learning olfaction.

New potential candidates for astronomical searches discovered in the electrical discharge of the PAH naphthalene and acetonitrile

The formation and dissociation mechanisms of polycyclic aromatic hydrocarbons (PAHs) as well as their reactivity with other interstellar molecules are elusive. In this work, we have investigated the electrical discharge chemistry of the PAH naphthalene and acetonitrile, a molecule known to be present in interstellar environments, using a combination of mass-selective IR-UV ion dip spectroscopy with the free electron laser FELIX in the mid-IR frequency region (550 – 1800 cm−1) and quantum chemical calculations. In addition to the species known to be produced in the electrical discharge of pure naphthalene, –CH3 and –CN substituted unsaturated hydrocarbons have been identified. Most of them, in particular those containing a nitrogen atom in the molecular framework, such as 7H-benzo[7]annulenecarbonitrile, have a substantial dipole moment and, therefore, can be considered as potential candidates for radio astronomical searches. Among the species observed, the two isomers 1- and 2-cyanonaphthalene, which have been recently detected in the TMC-1, have been identified in our experiment, thus continuing to highlight the use of electrical discharge sources as a valuable tool to produce astronomically relevant species.

The Chemical Nature of Orion Protostars: Are ORANGES Different from PEACHES? ORANGES II.

Abstract Understanding the chemical past of our Sun and how life appeared on Earth is no mean feat. The best strategy we can adopt is to study newborn stars located in an environment similar to the one in which our Sun was born and assess their chemical content. In particular, hot corinos are prime targets because recent studies have shown correlations between interstellar complex organic molecules abundances from hot corinos and comets. The ORion ALMA New GEneration Survey aims to assess the number of hot corinos in the closest and best analog to our Sun’s birth environment, the OMC-2/3 filament. In this context, we investigated the chemical nature of 19 solar-mass protostars and found that 26% of our sample sources show warm methanol emission indicative of hot corinos. Compared to the Perseus low-mass star-forming region, where the PErseus ALMA CHEmistry Survey detected hot corinos in ∼60% of the sources, the hot corinos seem to be relatively scarce in the OMC-2/3 filament. While this suggests that the chemical nature of protostars in Orion and Perseus is different, improved statistics is needed in order to consolidate this result. If the two regions are truly different, this would indicate that the environment is likely playing a role in shaping the chemical composition of protostars.

Quantum Mechanical Simulations of the Radical–Radical Chemistry on Icy Surfaces

Abstract The formation of the interstellar complex organic molecules (iCOMs) is a hot topic in astrochemistry. One of the main paradigms trying to reproduce the observations postulates that iCOMs are formed on the ice mantles covering the interstellar dust grains as a result of radical–radical coupling reactions. We investigate iCOM formation on the icy surfaces by means of computational quantum mechanical methods. In particular, we study the coupling and direct hydrogen abstraction reactions involving the CH3 + X systems (X = NH2, CH3, HCO, CH3O, CH2OH) and HCO + Y (Y = HCO, CH3O, CH2OH), plus the CH2OH + CH2OH and CH3O + CH3O systems. We computed the activation energy barriers of these reactions, as well as the binding energies of all the studied radicals, by means of density functional theory calculations on two ice water models, made of 33 and 18 water molecules. Then, we estimated the efficiency of each reaction using the reaction activation, desorption, and diffusion energies and derived kinetics with the Eyring equations. We find that radical–radical chemistry on surfaces is not as straightforward as usually assumed. In some cases, direct H-abstraction reactions can compete with radical–radical couplings, while in others they may contain large activation energies. Specifically, we found that (i) ethane, methylamine, and ethylene glycol are the only possible products of the relevant radical–radical reactions; (ii) glyoxal, methyl formate, glycolaldehyde, formamide, dimethyl ether, and ethanol formation is likely in competition with the respective H-abstraction products; and (iii) acetaldehyde and dimethyl peroxide do not seem to be likely grain-surface products.

Picosecond pulse-shaping for strong three-dimensional field-free alignment of generic asymmetric-top molecules

Fixing molecules in space is a crucial step for the imaging of molecular structure and dynamics. Here, we demonstrate three-dimensional (3D) field-free alignment of the prototypical asymmetric top molecule indole using elliptically polarized, shaped, off-resonant laser pulses. A truncated laser pulse is produced using a combination of extreme linear chirping and controlled phase and amplitude shaping using a spatial-light-modulator (SLM) based pulse shaper of a broadband laser pulse. The angular confinement is detected through velocity-map imaging of H+ and C2+ fragments resulting from strong-field ionization and Coulomb explosion of the aligned molecules by intense femtosecond laser pulses. The achieved three-dimensional alignment is characterized by comparing the result of ion-velocity-map measurements for different alignment directions and for different times during and after the alignment laser pulse to accurate computational results. The achieved strong three-dimensional field-free alignment of < {cos }^{2}delta > =0.89 demonstrates the feasibility of both, strong three-dimensional alignment of generic complex molecules and its quantitative characterization.

2021 Census of Interstellar, Circumstellar, Extragalactic, Protoplanetary Disk, and Exoplanetary Molecules

Abstract To date, 241 individual molecular species, composed of 19 different elements, have been detected in the interstellar and circumstellar medium by astronomical observations. These molecules range in size from two atoms to 70 and have been detected across the electromagnetic spectrum from centimeter wavelengths to the ultraviolet. This census presents a summary of the first detection of each molecular species, including the observational facility, wavelength range, transitions, and enabling laboratory spectroscopic work, as well as listing tentative and disputed detections. Tables of molecules detected in interstellar ices, external galaxies, protoplanetary disks, and exoplanetary atmospheres are provided. A number of visual representations of these aggregate data are presented and briefly discussed in context.

Controlling the Shrinkage of 3D Hot Spot Droplets as a Microreactor for Quantitative SERS Detection of Anticancer Drugs in Serum Using a Handheld Raman Spectrometer.

Quantitative measurement is one of the ultimate targets for surface-enhanced Raman spectroscopy (SERS), but it suffers from difficulties in controlling the uniformity of hot spots and placing the target molecules in the hot spot space. Here, a convenient approach of three-phase equilibrium controlling the shrinkage of three-dimensional (3D) hot spot droplets has been demonstrated for the quantitative detection of the anticancer drug 5-fluorouracil (5-FU) in serum using a handheld Raman spectrometer. Droplet shrinkage, triggered by the shaking of aqueous nanoparticle (NP) colloids with immiscible oil chloroform (CHCl3) after the addition of negative ions and acetone, not only brings the nanoparticles in close proximity but can also act as a microreactor to enhance the spatial enrichment capability of the analyte in plasmonic sites and thereby realize simultaneously controlling 3D hot spots and placing target molecules in hot spots. Moreover, the shrinking process of Ag colloid droplets has been investigated using a high-speed camera, an in situ transmission electron microscope (in situ TEM), and a dark-field microscope (DFM), demonstrating the high stability and uniformity of nanoparticles in droplets. The shrunk Ag NP droplets exhibit excellent SERS sensitivity and reproducibility for the quantitative analysis of 5-FU over a large range of 50-1000 ppb. Hence, it is promising for quantitative analysis of complex systems and long-term monitoring of bioreactions.

Non-energetic Formation of Ethanol via CCH Reaction with Interstellar H2O Ices. A Computational Chemistry Study.

Ethanol (CH3CH2OH) is a relatively common molecule, often found in star-forming regions. Recent studies suggest that it could be a parent molecule of several so-called interstellar complex organic molecules (iCOMs). However, the formation route of this species remains under debate. In the present work, we study the formation of ethanol through the reaction of CCH with one H2O molecule belonging to the ice as a test case to investigate the viability of chemical reactions based on a “radical + ice component” scheme as an alternative mechanism for the synthesis of iCOMs, beyond the usual radical–radical coupling. This has been done by means of DFT calculations adopting two clusters of 18 and 33 water molecules as ice models. Results indicate that CH3CH2OH can potentially be formed by this proposed reaction mechanism. The reaction of CCH with H2O on the water ice clusters can be barrierless (because of the help of boundary icy water molecules acting as proton-transfer assistants), leading to the formation of vinyl alcohol precursors (H2CCOH and CHCHOH). Subsequent hydrogenation of vinyl alcohol yielding ethanol is the only step presenting a low activation energy barrier. We finally discuss the astrophysical implications of these findings.

The Two Hot Corinos of the SVS13-A Protostellar Binary System: Counterposed Siblings

Abstract We present ALMA high-angular-resolution (∼50 au) observations of the Class I binary system SVS13-A. We report images of SVS13-A in numerous interstellar complex organic molecules: CH3OH, 13CH3OH, CH3CHO, CH3OCH3, and NH2CHO. Two hot corinos at different velocities are imaged in VLA4A (V sys = +7.7 km s−1) and VLA4B (V sys = +8.5 km s−1). From a non-LTE analysis of methanol lines, we derive a gas density of 3 × 108 cm−3 and gas temperatures of 140 and 170 K for VLA4A and VLA4B, respectively. For the other species, the column densities are derived from an LTE analysis. Formamide, which is the only N-bearing species detected in our observations, is more prominent around VLA4A, while dimethyl ether, methanol, and acetaldehyde are associated with both VLA4A and VLA4B. We derive in the two hot corinos abundance ratios of ∼1 for CH3OH, 13CH3OH, and CH3OCH3; ∼2 for CH3CHO; and ∼4 for NH2CHO. The present data set supports chemical segregation between the different species inside the binary system. The emerging picture is that of an onion-like structure of the two SVS13-A hot corinos, caused by the different binding energies of the species, also supported by ad hoc quantum chemistry calculations. In addition, the comparison between molecular and dust maps suggests that the interstellar complex organic molecules emission originates from slow shocks produced by accretion streamers impacting the VLA4A and VLA4B disks and enriching the gas-phase component.

Chemical survey of Class I protostars with the IRAM-30 m

Context. Class I protostars are a bridge between Class 0 protostars (≤105 yr old), and Class II (≥106 yr) protoplanetary disks. Recent studies show gaps and rings in the dust distribution of disks younger than 1 Myr, suggesting that planet formation may start already at the Class I stage. To understand what chemistry planets will inherit, it is crucial to characterize the chemistry of Class I sources and to investigate how chemical complexity evolves from Class 0 protostars to protoplanetary disks. Aims. There are two goals: (i) to perform a census of the molecular complexity in a sample of four Class I protostars, and (ii) to compare the data with the chemical compositions of earlier and later phases of the Sun-like star formation process. Methods. We performed IRAM-30 m observations at 1.3 mm towards four Class I objects (L1489-IRS, B5-IRS1, L1455-IRS1, and L1551-IRS5). The column densities of the detected species were derived assuming local thermodynamic equilibrium (LTE) or large velocity gradients (LVGs). Results. We detected 27 species: C-chains, N-bearing species, S-bearing species, Si-bearing species, deuterated molecules, and interstellar complex organic molecules (iCOMs; CH3OH, CH3CN, CH3CHO, and HCOOCH3). Among the members of the observed sample, L1551-IRS5 is the most chemically rich source. Different spectral profiles are observed: (i) narrow lines (~1 km s−1) towards all the sources, (ii) broader lines (~4 km s−1) towards L1551-IRS5, and (iii) line wings due to outflows (in B5-IRS1, L1455-IRS1, and L1551-IRS5). Narrow c-C3H2 emission originates from the envelope with temperatures of 5–25 K and sizes of ~2′′−10′′. The iCOMs in L1551-IRS5 reveal the occurrence of hot corino chemistry, with CH3OH and CH3CN lines originating from a compact (~0.′′15) and warm (T &gt; 50 K) region. Finally, OCS and H2S seem to probe the circumbinary disks in the L1455-IRS1 and L1551-IRS5 binary systems. The deuteration in terms of elemental D/H in the molecular envelopes is: ~10−70% (D2CO/H2CO), ~5−15% (HDCS/H2CS), and ~1−23% (CH2DOH/CH3OH). For the L1551-IRS5 hot corino we derive D/H ~2% (CH2DOH/CH3OH). Conclusions. Carbon chain chemistry in extended envelopes is revealed towards all the sources. In addition, B5-IRS1, L1455-IRS1, and L1551-IRS5 show a low-excitation methanol line that is narrow and centered at systemic velocity, suggesting an origin from an extended structure, plausibly UV-illuminated. The abundance ratios of CH3CN, CH3CHO, and HCOOCH3 with respect to CH3OH measured towards the L1551-IRS5 hot corino are comparable to that estimated at earlier stages (prestellar cores, Class 0 protostars), and to that found in comets. The deuteration in our sample is also consistent with the values estimated for sources at earlier stages. These findings support the inheritance scenario from prestellar cores to the Class I phase when planets start forming.