Solid-state Formation Research Articles

Providing a Window into the Phase Behavior of Semiconducting Polymers

The targeted assembly of a wealth of functional architectures for soft photonics and electronics relies on a rigorous understanding of semiconducting polymer phase behavior. While many useful correlations have been established in the field of commodity plastics, unifying theories for their semiconducting counterparts are, however, more challenging to develop because of the rich phase behavior frequently displayed by these macromolecules, due in part to their complex chemical structures typically based on relatively rigid backbones and elaborate side-chain motifs. Solid-state structure formation and resulting properties are therefore especially sensitive to thermal and temporal parameters during processing, rendering device fabrication a challenging task that too often relies on time-consuming trial-and-error procedures. To understand the thermodynamic and kinetic factors of plastic semiconductor solidification and, for example, thin-film growth relevant for device fabrication, detailed knowledge of the intricacies of macromolecular semiconductors’ phase behavior must be gained and ideally combined with temperature/composition, temperature/confinement, and/or time/temperature/transformation- phase diagrams. This will open pathways toward a knowledge and methodology platform for the controlled materials assembly of soft electronics/photonics systems very much in analogy to the approaches used in metallurgy and the inorganic electronic materials field. In turn, a step change in how we design and process soft electronic products might be achieved, with impact on the broader soft matter area.

Facile solid-state synthesis of layered molybdenum boride-based electrode for efficient electrochemical aqueous asymmetric supercapacitor

The survey of 2D materials has triggered the energy storage and conversion research. In molybdenum-based 2D layered materials are of great significance, due to their remarkable properties. In this work, simple solid-state synthesis and formation of molybdenum boride has been explored with various characteristic techniques. The advanced characterization techniques like XRD, TEM, XPS, BET, have been used to understand the crystallinity, morphology, and surface area of the layered MoB (LMB). The electrochemical performances of LMB electrode were verified with different aqueous electrolytes. The LMB electrode has been found to store higher charge in H2SO4 than Na2SO4 electrolyte. The LMB electrode delivered a specific capacitance of 445 F g−1 in H2SO4 where 130 F g−1 in Na2SO4 at a current density of 1 A g−1. Such behavior may be due to ionic size and mobility of ions in the electrolyte. The asymmetric supercapacitors have been fabricated with LMB and activated carbon (AC) electrode then the device performance was examined in both the electrolyte. On optimization, it was found the device works well in potential window 1.4 V in H2SO4 while the potential window was extended to 1.8 V in Na2SO4 electrolyte. The device was found to deliver an energy density of 14 W h kg−1 at a power density of 16.8 kW kg−1 for H2SO4 with a better capacity retention of 98% for 2000 cycles. Thus, LMB electrode in supercapacitor application has been demonstrated for the first time, which can instigate more investigations for layered molybdenum-based electrodes for energy storage devices.

Characterisation and fundamental insight into the formation of new solid state, multicomponent systems of propranolol

The physiochemical properties of acidic or basic active pharmaceutical ingredients (APIs) can be optimised by forming salts with different counterions. The aim of this work was to synthesise a novel salt of propranolol (PRO) using sebacic acid (SEBA) as the counterion and to gain mechanistic understanding of not only the salt formation, but also its eutectic phase formation with SEBA. Thermal analysis showed a solid-state reaction occurring between PRO and SEBA leading to the formation of dipropranolol sebacate (DPS) melting at app. 170 °C and the eutectic composed of DPS and SEBA melting at app. 103 °C, comprising 0.33 mol fraction of PRO as determined by the Tammann plot. X-ray diffraction and Fourier-transform infrared spectroscopy (FTIR) confirmed the identity of the new multicomponent phases of PRO. DPS can be conveniently obtained by heat-induced crystallisation, grinding and conventional solvent crystallisation. Detailed analysis by FTIR revealed H-bond interactions between DPS and SEBA at the inter-phase in the eutectic. Bravais, Friedel, Donnay and Harker crystal morphology coupled with full interaction maps analysis allowed to understand further the nature of interactions which led to formation of the eutectic phase. This work contributes to furthering research on multicomponent pharmaceutical systems to harness their full potential.

Gapped magnetic ground state in quantum spin liquid candidate κ-(BEDT-TTF)2Cu2(CN)3.

Geometrical frustration, quantum entanglement, and disorder may prevent long-range ordering of localized spins with strong exchange interactions, resulting in an exotic state of matter. κ-(BEDT-TTF)2Cu2(CN)3 is considered the prime candidate for this elusive quantum spin liquid state, but its ground-state properties remain puzzling. We present a multifrequency electron spin resonance (ESR) study down to millikelvin temperatures, revealing a rapid drop of the spin susceptibility at 6 kelvin. This opening of a spin gap, accompanied by structural modifications, is consistent with the formation of a valence bond solid ground state. We identify an impurity contribution to the ESR response that becomes dominant when the intrinsic spins form singlets. Probing the electrons directly manifests the pivotal role of defects for the low-energy properties of quantum spin systems without magnetic order.

Solid-State Dissimilar Film Formation for Metals, Ceramics, and Polymers by Cold Spray Technique

Solid-State Dissimilar Film Formation for Metals, Ceramics, and Polymers by Cold Spray Technique

The coordination chemistry of benzhydrazide with lanthanide(iii) ions: hydrothermal in situ ligand formation, structures, magnetic and photoluminescence sensing properties.

The influence of synthetic conditions on the solid-state structural formation of lanthanide(iii) complexes based on a hydrazide ligand have been investigated and reported. Depending on the solvents and reaction temperatures, the reactions of hydrated Ln(NO3)3 with a benzohydrazide (bzz) ligand afforded three classes of lanthanide(iii) coordination complexes viz. [Ln(bzz)(NO3)](NO3)2 (1Ln; Ln = Sm (1), Eu (2), Gd (3), Tb (4), Dy (5)), [Ln(bzz)(ben)3(H2O)]·H2O (2Ln; Ln = Pr (6), Nd (7), Sm (8), Eu (9), Gd (10), Tb (11), Dy (12), Er (13)), and [Ln3(ben)3] (3Ln; Ln = Eu (14), Gd (15), Tb (16), Dy (17), Er (18), Tm (19), Yb (20), Lu (21)). Complexes 1–5 in series 1Ln were isolated by slow evaporation of their isopropanol solutions at ambient temperature, and the complexes display similar discrete structures bearing distinct intermolecular N–H⋯O hydrogen bonds to generate a three-dimensional (3D) supramolecular architecture. Complexes 6–13 in series 2Ln were obtained under hydrothermal conditions at 110 °C where the in situ generated benzoate (ben) ligands participated in the formation of one-dimensional (1D) coordination polymers (CPs) with the bzz ligands. At a temperature of 145 °C the hydrothermal conditions result in the formation of the thermodynamically more stable products of 14–21 in series 3Ln, in which the bzz ligand underwent complete in situ hydrolysis to create the ben ligand. These coordination assemblies feature 1D zigzag chains that are formed by unusual low coordination numbers of the six- and seven-fold coordinated Ln3+ centers bridged by the ben ligands in μ2- and μ3-coordination modes. Notably, the chain structures of 2Ln can be transformed into the zigzag tape-like structures of 3Ln upon heating the crystalline samples to 400 °C in air. In the solid state at room temperature, the Eu- (2, 9, 14) and Tb- (4, 11, 16) containing complexes emit red and green light, respectively. The luminescence investigations show that the Eu- (9, 14) and Tb-(11, 16) based CPs could be used as fluorescent probes for acetone and Co2+ ions via an energy competition mechanism. Meanwhile, the Gd- (10, 15) and Dy- (12, 17) based CPs show typical antiferromagnetic interactions.

Learning to fly: thermochemistry of energetic materials by modified thermogravimetric analysis and highly accurate quantum chemical calculations.

The standard state enthalpy of formation and the enthalpy of sublimation are essential thermochemical parameters determining the performance and application prospects of energetic materials (EM). Direct experimental measurements of these properties are complicated by low volatility and high heat release in bomb calorimetry experiments. As a result, the uncertainties in the reported enthalpies of formation for a number of even well-known CHNO-containing compounds might amount up to tens kJ mol-1, while for some novel high-nitrogen molecules they reach even hundreds of kJ mol-1. The present study reports a facile approach to determining the solid-state formation enthalpies comprised of complementary high-level quantum chemical calculations of the gas-phase thermochemistry and advanced thermal analysis techniques yielding sublimation enthalpies. The thermogravimetric procedure for the measurement of sublimation enthalpy was modified by using low external pressures (down to 0.2 Pa). This allows for observing sublimation/vaporization instead of thermal decomposition of the compounds studied. Extensive benchmarking on nonenergetic and energetic compounds reveals the average and maximal absolute errors of the sublimation enthalpies of 3.3 and 11.0 kJ mol-1, respectively. The comparison of the results with those obtained from the widely used Trouton-Williams empirical equation shows that the latter underestimates the sublimation enthalpy up to 140 kJ mol-1. Therefore, we performed a reparametrization of the latter equation with simple chemical descriptors that reduces the mean error down to 30 kJ mol-1. Highly accurate multi-level procedures W2-F12 and/or W1-F12 in conjunction with the atomization energy approach were used to calculate theoretically the gas-phase formation enthalpies. In several cases, the DLPNO-CCSD(T) enthalpies of isodesmic reactions were also employed to obtain the gas-phase thermochemistry for medium-sized important EMs. Combining the obtained thermochemical properties, we determined the solid-state enthalpies of formation for nearly 60 species containing various important explosophoric groups, from common nitroaromatics, nitroethers, and nitramines to novel nitrogen-rich heterocyclic species (e.g., the derivatives of pyrazole, tetrazole, furoxan, etc.). The large-scale benchmarking against the available experimental solid-state enthalpies of formation yielded the maximal inaccuracy of the proposed method of 25 kJ mol-1.

The TW Hya Rosetta Stone Project. II. Spatially Resolved Emission of Formaldehyde Hints at Low-temperature Gas-phase Formation

Abstract Formaldehyde (H2CO) is an important precursor to organics like methanol (CH3OH). It is important to understand the conditions that produce H2CO and prebiotic molecules during star and planet formation. H2CO possesses both gas-phase and solid-state formation pathways, involving either UV-produced radical precursors or CO ice and cold (≲20 K) dust grains. To understand which pathway dominates, gaseous H2CO's ortho-to-para ratio (OPR) has been used as a probe, with a value of 3 indicating “warm” conditions and <3 linked to cold formation in the solid state. We present spatially resolved Atacama Large Millimeter/submillimeter Array observations of multiple ortho- and para-H2CO transitions in the TW Hya protoplanetary disk to test H2CO formation theories during planet formation. We find disk-averaged rotational temperatures and column densities of 33 ± 2 K, (1.1 ± 0.1) × 1012 cm−2 and 25 ± 2 K, (4.4 ± 0.3) × 1011 cm−2 for ortho- and para-H2CO, respectively, and an OPR of 2.49 ± 0.23. A radially resolved analysis shows that the observed H2CO emits mostly at rotational temperatures of 30–40 K, corresponding to a layer with z/R ≥ 0.25. The OPR is consistent with 3 within 60 au, the extent of the pebble disk, and decreases beyond 60 au to 2.0 ± 0.5. The latter corresponds to a spin temperature of 12 K, well below the rotational temperature. The combination of relatively uniform emitting conditions, a radial gradient in the OPR, and recent laboratory experiments and theory on OPR ratios after sublimation, led us to speculate that gas-phase formation is responsible for the observed H2CO across the TW Hya disk.

Isothermal and Isoconversional Modeling of Solid-State Nitroso Polymerization.

The solid-state formation of azodioxide polymers from aromatic dinitroso compounds with different spacer groups was used as a model reaction for a comprehensive analysis that included bulk-based, mechanistic, and isoconversional kinetic methods. Dinitroso species were prepared in situ from azodioxides by UV cleavage under cryogenic conditions, after which their thermally induced conversion to azodioxides was followed by Fourier transform IR spectroscopy. The obtained data were used to calculate activation parameters and determine the influence of the spacer on the kinetics. Isoconversional models suggest a distribution of activation energies, pointing to an important (topochemical) effect of the local environment on the reactivity. In general, bulk-based and isoconversional kinetic models gave poorer fits but produced mutually consistent rate parameters. Similar energies and entropies of activation were obtained with all three approaches, suggesting that they all describe the same underlying physical phenomena; that is, the polymerization by bond-making is the dominant process.

Structural features modeling of substituted hydroxyapatite nanopowders as bone fillers via machine learning

In the present study, both experimental and modeling approaches were employed to explore the solid-state formation mechanisms and estimate the structural behavior of nanosized substituted hydroxyapatite (HA) powders using different machine learning (ML) techniques. In the phase of modeling, an artificial neural network (ANN)-based method, called multi-layer perceptron (MLP), was used to truthfully approximate structural characteristics of the as-received nanopowders. In the next round of modeling, the genetic programming (GP) technique was employed to appraise the strength of the predictive model. Following the modeling procedure, a few case studies were conducted to evaluate the results obtained by the modeling framework, where the microstructural alterations of the mechanosynthesized substituted nanopowders were examined in terms of the dopant agent. The Rietveld refinement showed a good fit of the observed and calculated profiles over the full diffraction patterns. With the effect of dopant type, different levels of weight loss were observed in the thermal analysis curves. The comparison between the proposed models ascertained that both models were truthful for the estimation of the structural features of HA-based bioceramics for different bone regeneration applications. From the statistical assessments, the values of Mean Squared Error (MSE) and Correlation Coefficient (R) of the MLP-ANN in the training phase for the crystallite size were 5.757 and 0.93, which in prediction reached 3.429 and 0.995, respectively.

A new multi-beam apparatus for the study of surface chemistry routes to formation of complex organic molecules in space.

A multi-beam ultra-high vacuum apparatus is presented. In this article, we describe the design and construction of a new laboratory astrophysics experiment-VErs de NoUvelles Synthèses (VENUS)-that recreates the solid-state non-energetic formation conditions of complex organic molecules in dark clouds and circumstellar environments. The novel implementation of four operational differentially pumped beam lines will be used to determine the feasibility and the rates for the various reactions that contribute to formation of molecules containing more than six atoms. Data are collected by means of Fourier transform infrared spectroscopy and quadrupole mass spectrometry. The gold-coated sample holder reaches temperatures between 7 K and 400 K. The apparatus was carefully calibrated and the acquisition system was developed to ensure that experimental parameters are recorded as accurately as possible. A great effort has been made to have the beam lines converge toward the sample. Experiments have been developed to check the beam alignment using reacting systems of neutral species (NH3 and H2CO). Preliminary original results were obtained for the {NO + H} system, which shows that chemistry occurs only in the very first outer layer of the deposited species, that is, the chemical layer and the physical layer coincide. This article illustrates the characteristics, performance, and future potential of the new apparatus in view of the forthcoming launch of the James Webb Space Telescope. We show that VENUS will have a major impact through its contributions to surface science and astrochemistry.

Realization of Separated Imprinting Fabrication Process Driven from Interfacial Wetting Mechanism for Durable Perovskite and Organic Photovoltaic Devices

Recently, fabrication procedure has become a key factor directly related to the efficiency and cost reduction of products. Despite the importance of process improvement, due to the limitations of the application range, many fabrication processes are limited to laminating one by one. Particularly, when applied to a roll-to-roll process, since the only method is to increase the length of the rail for heat treatment and drying time, realization of the separated fabrication process can minimize waste. One of the separated imprinting processes, transfer process using by soft mold, has been considered by advanced technology to overcome limits of conventional lamination process (spin-casting, dip-coating, etc.), because a layer is previously formed on the other medium substrate, as well as the material loss and penetration of solvents are minimized in the process.In this research, we introduced polyurethane acylate (PUA) of which the surface property was modified by applying the various functional group of the monomer, because control of the surface property of the medium was required to minimize interfacial wettability with a material. As a result, we designed the proper PUAs to enable the transfer process of each organic semiconductor via adhesion control between each interface. First, we applied the transfer process to inter-layer in planer-type perovskite photovoltaics. We successfully transferred two types of inter-layer, poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS) [1], and 6,6-phenyl-C71 butyric acid methyl ester (PC71BM) [2]. Interestingly, when the PEDOT:PSS was transferred onto Indium tin oxide (ITO) substrate, the corrosion of ITO was extremely suppressed due to solid-state film formation, which enhanced the stability of the perovskite devices. Especially, the device with transferred PC71BM exhibited the performance improvement caused by improved coverage of inter-layer on perovskite layer, correlated with increased electron mobility and exciton dissociation. Finally, the transfer process was introduced to organic photodiode (OPD) fabrication [3]. Despite the separated imprinting system, a comparable performance was confirmed in the OPD from the transfer process. Furthermore, the OPD with transferred sensitive layer showed a superior durability (over 95%) to the device from conventional process, owing to morphology stabilization of organic semiconductor layers. This work provides a strategy for promising next-generation technologies of separated imprinting fabrication process, and at the same time can make a significant contribution to increase of process yield and reduction of unit prices.[1] M. Yi, W. Jang, J. S. Cho, and D. H. Wang, Appl. Surf. Sci., 2019, 467, 168.[2] S. Ahn, W. Jang, S. Park, and D. H. Wang, ACS Appl. Mater. Interfaces, 2017, 9, 15623.[3] W. Jang, and D. H. Wang, ACS Appl. Mater. Interfaces, 2018, 10, 38603.

Open versus Interpenetrated: Switchable Supramolecular Trajectories in Mechanosynthesis of a Halogen-Bonded Borromean Network

Summary Precise control over topologically intricate molecular architectures remains an open challenge for chemists due to their inherent structural complexity. We report a simple solvent-free strategy to selectively prepare two multi-component supramolecular crystalline systems based on the halogen bond, endowed with either an unknot topology or a Borromean-type entanglement. Real-time in situ monitoring of the solvent-free mechanochemical synthesis of these three-component halogen-bonded ionic co-crystals reveals that the choice of milling conditions leads to a switch in the supramolecular reaction trajectory, resulting in the selective formation of an open halogen-bonded network or a halogen-bonded Borromean-type assembly.

Raman and Terahertz Spectroscopic Characterization of Solid-state Cocrystal Formation within Specific Active Pharmaceutical Ingredients.

Cocrystallization of specific active pharmaceutical ingredients (APIs) in the solid-state phase is becoming a feasible way to improve their corresponding physicochemical properties and ultimate bioavailability without making and breaking any covalent bonds within them. Many recent reports deal with the characterization and analysis topics of pharmaceutical APIs-based cocrystals. In this mini-review, we will focus on the recent steady-state and time-dependent spectroscopic investigation into the cocrystallization of specific APIs based on both Raman and emerging terahertz spectroscopy in pharmaceutical fields. Distinctive spectral, structural and also kinetic information of pharmaceutical APIs-based cocrystals are obtained and discussed, which would highlight the potential of vibrational spectroscopy as an attractive technique for various drug research and development during cocrystallization of specific APIs.

Host-guest inclusion complex of β-cyclodextrin and 4,4′-(1,4-phenylenediisopropylidene)bisaniline: Spectral, structural and molecular modeling studies

The Host-Guest inclusion complex of β-Cyclodextrin (β-CD) and 4,4′-(1,4-phenylenediisopropylidene)bisaniline (PDB) was prepared in solid and solution state and characterized by UV-Visible, Fluorescence, FT-IR, Time resolved fluorescence spectroscopy, DSC, SEM, AFM, XRD and Molecular modeling approach. These studies were adopted to approve the formation of PDB: β-CD inclusion complex . Job's plot and Benesi-Hildebrand plot obtained by using UV and Fluorescence spectral readings confirmed the 1:2 PDB: β-CD complex formation.. FT-IR study revealed that aromatic rings of PDB are partially encapsulated in to the β-CD cavity. The interaction between PDB and β-CD is shown by enhancement of thermal stability of PDB after the complexation. AFM and SEM analysis were also confirmed inclusion complex formation in solid state. Molecular docking study revealed the fact that 1:2 inclusion complex possesses a good molecular shape complementarity score for its most probable structure.

Olefin polymerization behavior of titanium(IV) alkoxo complexes with fluorinated diolate ligands: The impact of the chelate ring size and the nature of organoaluminum compounds

Titanium(IV) coordination compounds are effectively used as precatalysts for ethylene polymerization and copolymerization with other olefins. New titanium(IV) complexes 3b–d with ligands containing two diphenylcarbinol fragments linked by the perfluorinated hydrocarbon units –CF2– or –C2F4– were synthesized. The structures of complexes 3b and 3d were determined by X‐ray diffraction. Titanium atoms in 3b have a distorted trigonal‐bipyramidal coordination environment while spiro‐complex 3d is characterized by tetrahedral molecular geometry. The catalytic behavior of complexes activated by mixtures of Bu2Mg and alkylaluminium chlorides from among Me2AlCl, Et2AlCl, EtAlCl2, and Et3Al2Cl3 were studied. The resulting catalytic systems catalyze ethylene polymerization to afford ultra‐high molecular weight polyethylene, suitable for modern processing methods, and the solvent‐free solid state formation of super high‐strength (1.37–2.75 GPa) and high‐modulus (up to 138 GPa) oriented film tapes. The same catalytic systems catalyze ethylene copolymerization with 1‐hexene to afford high molecular weight semicrystalline elastomeric polymers containing up to 20% of comonomer units.

Detection of glyceraldehyde and glycerol in VUV processed interstellar ice analogues containing formaldehyde: a general formation route for sugars and polyols

ABSTRACT Complex organic molecules (COMs) have been identified toward high- and low-mass protostars as well as molecular clouds. Among them, sugar-like and polyol two carbon-bearing molecules such as glycolaldehyde (GA) and ethylene glycol (EG) are of special interest. Recent laboratory experiments have shown that they can efficiently be formed via atom addition reactions between accreting H-atoms and CO molecules or via energetic processes (UV, electrons) on ice analogues containing methanol or formaldehyde. In this study, we report new laboratory experiments on the low-temperature solid state formation of complex organic molecules – the first sugar glyceraldehyde and its saturated derivative glycerol – through VUV photolysis performed at three different temperatures (15, 50, and 90 K) of astrochemically relevant ices composed of water and formaldehyde. We get evidence that the species production depends on the ice temperature during photolysis. The results presented here indicate that a general scheme of aldose and polyol formation is plausible and that heavier COMs than GA and EG could exist in interstellar environments. We propose a general pathway involving radical-formaldehyde reactions as common initiation step for aldose and polyol formation. Future telescope observations may give additional clues on their presence in star-forming regions as observations are currently limited because of the detection thresholds.

A cryogenic ice setup to simulate carbon atom reactions in interstellar ices.

The design, implementation, and performance of a customized carbon atom beam source for the purpose of investigating solid-state reaction routes in interstellar ices in molecular clouds are discussed. The source is integrated into an existing ultrahigh vacuum setup, SURFace REaction SImulation DEvice (SURFRESIDE2), which extends this double atom (H/D, O, and N) beamline apparatus with a third atom (C) beamline to a unique system that is fully suited to explore complex organic molecule solid-state formation under representative interstellar cloud conditions. The parameter space for this system is discussed, which includes the flux of the carbon atoms hitting the ice sample, their temperature, and the potential impact of temperature on ice reactions. Much effort has been put into constraining the beam size to within the limits of the sample size with the aim of reducing carbon pollution inside the setup. How the C-atom beam performs is quantitatively studied through the example experiment, C + 18O2, and supported by computationally derived activation barriers. The potential for this source to study the solid-state formation of interstellar complex organic molecules through C-atom reactions is discussed.

Formation of NH2CHO and CH3CHO upon UV Photoprocessing of Interstellar Ice Analogs

Abstract Complex organic molecules (COMs) can be produced by energetic processing of interstellar ice mantles accreted on top of dust grains. Two COMs with proposed energetic ice formation pathways are formamide and acetaldehyde. Both have been detected in solar system comets and in different circumstellar and interstellar environments. In this work, we study the NH2CHO and CH3CHO formation upon UV photoprocessing of CO:NH3 and CO:CH4 ice samples. The conversion from radicals to NH2CHO is 2–16 times higher than the conversion from radicals to CH3CHO under the explored experimental conditions, likely because the formation of the latter competes with the formation of larger hydrocarbons. In addition, the conversion of into NH2CHO at 10 K increases with the NH3 abundance in the ice, and also with the temperature in CO-dominated CO:NH3 ices. This is consistent with the presence of a small and HCO. reorientation barrier for the formation of NH2CHO, which is overcome with an increase in the ice temperature. The measured NH2CHO and CH3CHO formation efficiencies and rates are similar to those found during electron irradiation of the same ice samples under comparable conditions, suggesting that both UV photons and cosmic rays would have similar contributions to the solid-state formation of these species in space. Finally, the measured conversion yields (up to one order of magnitude higher for NH2CHO) suggest that in circumstellar environments, where the observed NH2CHO/CH3CHO abundance ratio is ∼0.1, there are likely additional ice and/or gas-phase formation pathways for CH3CHO.

Deep search for hydrogen peroxide toward pre- and protostellar objects

Context. In the laboratory, hydrogen peroxide (HOOH) was proven to be an intermediate product in the solid-state reaction scheme that leads to the formation of water on icy dust grains. When HOOH desorbs from the icy grains, it can be detected in the gas phase. In combination with water detections, it may provide additional information on the water reaction network. Hydrogen peroxide has previously been found toward ρ Oph A. However, further searches for this molecule in other sources failed. Hydrogen peroxide plays a fundamental role in the understanding of solid-state water formation and the overall water reservoir in young stellar objects (YSOs). Without further HOOH detections, it is difficult to assess and develop suitable chemical models that properly take into account the formation of water on icy surfaces. Aims. The objective of this work is to identify HOOH in YSOs and thereby constrain the grain surface water formation hypothesis. Methods. Using an astrochemical model based on previous work in combination with a physical model of YSOs, the sources R CrA-IRS 5A, NGC C1333-IRAS 2A, L1551-IRS 5, and L1544 were identified as suitable candidates for an HOOH detection. Long integration times on the APEX 12 m and IRAM 30 m telescopes were applied to search for HOOH signatures in these sources. Results. None of the four sources under investigation showed convincing spectral signatures of HOOH. The upper limit for HOOH abundance based on the noise level at the frequency positions of this molecule for the source R CrA-IRS 5A was close to the predicted value. For NGC 1333-IRAS 2A, L1544, and L1551-IRS 5, the model overestimated the hydrogen peroxide abundances. Conclusions. HOOH remains an elusive molecule. With only one secure cosmic HOOH source detected so far, namely ρ Oph A, the chemical model parameters for this molecule cannot be sufficiently well determined or confirmed in existing models. Possible reasons for the nondetections of HOOH are discussed.