Pablo del Mazo Sevillano, new doctor

On January 25th 2021, Pablo del Mazo Sevillano has defended in the Autonomous University of Madrid his PhD work entitled “Superficie de energía potencial y dinámica para la reacción H2CO + OH” (Potential Energy Surface and Dynamics for H2CO + OH reaction) supervised by professors Octavio Roncero Villa (IFF-CSIC) and Alfredo Aguado Gómez (UAM). Congratulations!

In this text, he explains the content of his tesis:

“The mechanism by which complex organic molecules (COMs) are found in the dense molecular clouds in the interstellar medium (ISM) has been assumed to proceed through their formation on ices. Later, as these ices evolve to hotter regions, the COMs would be released to the gas phase. Nevertheless, this complex organic molecules have been found in cold regions, shielded from UV-radiation, so it is mandatory to rethink this process.

One possible explanation comes from the results shown by CRESU experiment. In particular, it has been found that reactions between COMs and OH exhibit a huge increase in their kinetic rate constants as temperature decreases, what is surprising for reactions that usually present a barrier, hence should have an Arrhenius-like behavior. This opens the possibility of gas phase reactivity that has been previously dismissed. Unfortunately, there is no current experimental setup that can reproduce the conditions found in the ISM, in particular, the low pressure, so it is not possible to calculate the zero-pressure kinetic rate constants to be used in the astrochemical models. It is here that we can take some advantage from the computational simulations, since it is much easier to reproduce this low pressure conditions. In this PhD work we have focused on the simulation of the reactive process between H2CO + OH to form HCO + H2O and HCOOH + H, to evaluate the zero-pressure kinetic rate constants and provide a dynamical explanation of its behavior with temperature.

The dynamical simulation of a reactive process usually involves two steps:

First we must obtain the potential energy surface (PES) of the process. The PES is a function that encodes the energy for every nuclear configuration the system can reach during the simulation. It is from this function that the classical forces the system experience emerge, so a correct description of this function is crucial. In this work we have explored and propose different methodologies to express this function, with special interest in the use of artificial neural networks (ANN). ANNs are functions that present huge flexibility along with a short evaluation time, what makes them an excellent alternative to describe a PES.

The second step is the dynamical simulation itself. Once the interactions between particles are known (the PES) it is possible simulate collisions between the reactive partners and determine whether they react or not. From this, the kinetic rate constant can be calculated. In this work we have employed two methods: a quassiclassical  trajectory  method (including the zero-point energy of the reactants only at the beginning of dynamical calculations) and a Ring-polymer Molecular dynamics (RPMD) method (based on path integral and including quantum effects through the use of replicas or beads), to include quantum effects important at the low temperatures considered,  such as zero-point energy and tunneling. We found two key aspects that explain the increase of the kinetic rate constant for HCO + H2O formation as temperature lowers. On the one hand, due to the permanent dipole moment present in both reactants there is a very efficient capture mechanism at long distances. That way, reactants that are far away feel each other and start approaching until they finally collide. On the other hand, during this approach and finally collision, translational energy is transferred to rotation and vibration. This means that once the energy transfer is produced, it is not so easy for the system to redissociate back to reactants and the system gets trap for long times in a reactive complex. During this time the system has plenty of time to explore the configuration space, increasing the probability that reaction may take place. This is the mayor reaction mechanism for temperatures below 200 K, as has been found both experimentally and theoretically. Above this temperature, the direct mechanism becomes more important, leading to the well-known Arrhenius behavior”.

Representation of a PES (blue surface) over which a trajectory is being propagated (red line). Molecular geometries along the trajectory are shown.

Old and new

Bet on what we already have

40m Yebes Telescope at the Astronomical Center of Yebes (Spain)

Those who know me know that I am a strong advocate of betting on the development of technology in telescopes. Not for nothing did I work for a while for the Gran Telescopio Canarias and I saw how its level of competitiveness was endangered by not investing enough at the time: they would have left us with a great telescope, but without frontier instruments to get the best out of it.

Over time I have ended up working on a branch of astronomy that observes what happens in the coldest ranges of the light spectrum. In these ranges radioantennas are used, and in Spain we have a few installed.

In recent decades other countries have built and improved similar facilities. And it’s ugly to say it, but few bet on this antenna that I’m going to talk about when there were others that were yielding very good results in terms of accuracy and sensitivity.

A few weeks ago I attended online a talk by José Cernicharo (researcher at the Institute of Fundamental Physics of the CSIC), recently awarded the Miguel Catalán Prize 2020 for the scientific career, awarded by the Community of Madrid. The talk, designed to make known to people of the guild the latest results obtained, was a mixture of passion and joys. Cernicharo has been working all his life in the study of space chemistry and molecular astrophysics. In recent years he coordinates the European project NANOCOSMOS together with two other principal investigators, Christine Joblin (CNRS, France) and José Ángel Martín Gago (ICMM-CSIC, Spain). Nanocosm is a challenge in all its facets, since it pushes the frontier of knowledge with a risky and complex proposal. Not surprisingly, the Synergy Grants granted by the ERC (European Research Council) are bets that seek this difficulty, even at the risk of not obtaining the results originally intended. That is how science is and that is how it must be defended.

Machines to know the smallest universe

The case of Nanocosmos is a step towards discovery that unites science and technology, with several machines developed within the project that are giving surprising results.

The Stardust machine is a machine built from scratch, using, of course, the knowledge of those who have a lot of experience in surface science, but with objectives specifically aimed at clearing up unknowns related to astrochemistry, with knowing how dust grains are formed in the envelopes of evolved stars.

Developed at the Institute of Materials Science of Madrid (ICMM-CSIC) by José Ángel Martín Gago and his team, this machine is capable of synthesizing dust grains “a la carte” and make them go through several phases to determine their behavior under specific physical conditions. This helps us to confirm what is observed with antennas and telescopes.

The GACELA (Gas Cell for Chemical Evolution) simulation camera has been that link that unites the new and the old. Installed in Yebes, it uses the same receivers that have been installed in the 40m Yebes radio antenna. This camera studies the interaction of small particles with the earth’s primitive atmosphere and has a very high precision to define the composition of the gas.

Finally, the AROMA machine serves to take this later step in the analysis: the samples obtained in the Stardust machine and in GACELA are analyzed.

These three machines are the protagonists of this short, ten-minute video, which talks about how they work and what their first results have been. They help us to complete the puzzle of information offered by simulations, observations and, finally, the experiments themselves. In fact, there’s a phrase I can’t forget from an interview I did some time ago with Louis Le Sergeant d’Hendecourt (of the Astrochemistry and Origins team at the Institute of Space Astrophysics (CNRS-UPS) in France): “Laboratory astrophysics is the supreme judge in astrochemistry.”

New receivers, increased sensitivity

The Astronomical Center of Yebes (Centro Astronómico de Yebes, National Geographic Institute, Spain) has several tools, and one of them, the largest, is the 40m radio antenna of Yebes. Since 2010, it has focused on Very Long Baseline Interferometry (VLBI), acting in conjunction with other radio antennas located at different points on the planet, as well as single antenna observations, acting alone. It has been covering specific frequency bands (mainly between 2 GHz and 90 GHz in discontinuous and narrow windows) in order to meet the current needs of the European VLBI Network (EVN) and the The Global mm-VLBI Array (GMVA).

But the Nanocosmos project decided to bet on improving its performance, providing specific receivers aimed at meeting the objectives of the project. To be honest, we’re so used to betting on new things and discarding the “old” that sometimes we’re not aware of how valuable some tools are. In fact, Japanese researchers did something similar with the Nobeyama’s 45m Telescope, but the level of sensitivity obtained by the 40m Yebes Telescope is much higher.

The combination of the old and the new has been overwhelming: the teamwork developed by all the staff of the Astronomical Center of Yebes, together with the commitment of Nanocosmos, has managed to increase the instantaneous coverage of frequencies to observe numerous molecular transitions simultaneously. This reduces observation time and maximizes data output from the telescope (this paper describes the technical specifications of these receivers). It highlights the improvement in sensitivity in the Q band (but also in the W), with observational results that open the possibility of studying the spectrum of different astrophysical environments with an unprecedented sensitivity.

La primera muestra de ello es un barrido espectral que puede considerarse como una hazaña. Ya durante la fase de pruebas de los receptores se realizaron observaciones de muy alta sensibilidad, revelando el enorme potencial del nuevo equipamiento del radiotelescopio: en muy poco tiempo se han descubierto 11 nuevas moléculas (y lo que queda por descubrir).

The first example of this is a spectral sweep that can be considered a feat. Already during the testing phase of the receivers, observations of very high sensitivity were made, revealing the enormous potential of the new equipment of the radio telescope: in a very short time 11 new molecules have been discovered (and what remains to be discovered).

The TMC-1 sweep and IRC+10216 observations

TMC stands for Taurus Molecular Cloud. It is a nursery of newborn stars just 430 light years away, which makes it the molecular cloud with the closest stellar nursery to Earth and, therefore, a perfect “laboratory” for study. It stands out for the abundance of complex molecules, many of them studied and/or discovered by members of the Nanocosm team.

The spectral scan has been so deep and has reached so much sensitivity that the number of molecules discovered in record time has skyrocketed. Specifically, the protagonists (which we will reveal) are anions, protonated molecules and metastable isomers.

For now, stay with the idea that the 40m antenna of Yebes, with its new receivers, surpasses everything done previously, and that the combination between the observations made with the radio antenna and the experiments carried out with the GACELA camera, which has, remember, the same receivers as the antenna, will give incredible results. It’s already giving them. The widespread enthusiasm that was breathed in the atmosphere on the day of the online chat was real and totally tangible. Because science, despite its difficulties, continues to take steps to expand our knowledge.

Originally published in Spanish on the Naukas website: “De lo nuevo y lo viejo” (2021/02/15).

Sarah Massalkhi, new Doctor

On December 18th 2020, Sarah Massalkhi has defended in the Autonomous University of Madrid her PhD work entitled “An Observational Study of Molecular Dust Precursors in Circumstellar Envelopes” supervised by professors Marcelino Agúndez and José Cernicharo (IFF-CSIC). Congratulations!

Circumstellar envelopes around evolved stars of AGB type are probably the main factories of dust in the Universe. However, we still do not understand the process that operates in these environments to convert simple gas-phase molecules into large dust grains. In this thesis, we carried out an observational study to determine the abundance of molecules that could potentially act as precursors of dust in a large sample of AGB stars using the radiotelescope IRAM 30m.

Among the main results, in C-rich AGB envelopes we find a clear trend in which the fractional abundance of SiC2, SiO, y CS decreases as the envelope density increases, which we interpret as an evidence of efficient incorporation of these molecules onto dust grains, suggesting that that they are strong candidates to act as precursors of dust in C-rich envelopes. Likewise, SiO shows the same trend in O-rich envelopes, suggesting that it actively contributes to the formation of dust in these environments. We also find that the studied molecules have different behaviors with respect to the C- or O-rich character of the envelope, with molecules like CS and SiS showing a clear differentiation between these two types of envelopes while SiO does not seem to be sensitive to the C/O ratio.

José Cernicharo, awarded with the “Miguel Catalán” 2020 prize

José Cernicharo, Researcher of the IFF-CSIC and Head of our group, has been awarded the “Miguel Catalán” 2020 Prize for his scientific career within the research awards of the Community of Madrid, “for the quality of his research, his recognized leadership at national and international level in the area of Molecular Astrophysics and for his contributions and technological innovations”.

The Community of Madrid convenes annually the Research Awards “Miguel Catalán” and “Julián Marías” to the scientific career, in order to recognize scientific activity, as well as the scientific and humanistic values developed by researchers who throughout their professional career have been in some way linked to the Community of Madrid, and the Research Awards of the Community of Madrid “Miguel Catalán” and “Julián Marías” to researchers of less than forty years , in order to recognize the quality and excellence of scientific and research work developed at the beginning of his research career. They are convened annually in the two Areas, Sciences and Humanities.

The ceremony, which will take place tomorrow, November 20 at 10:30, can be followed online through the following links:

  1. Madrid Community Canal
  2. Twitter of the Community of Madrid
  3. Complutense University Of Madrid Canal
  4. Youtube from the Complutense University of Madrid

Funambulist stars

Why do we study chemical equilibrium in red giants?

You may have often read that “we are stardust.” It is a rather accurate expression, especially if we think that most of the elements that make us up (this scarce 5% of the baryonic matter of the universe) emerged from the core of a star and from a whole process of death and destruction. But what do we call stardust?

Medium-sized stars (between one and eight solar masses) go through several phases throughout their lives. The longest phase is the so-called  “main sequence”, in which time is spent transforming hydrogen into helium. When hydrogen from the nucleus (where this activity occurs in principle) is depleted, the star begins to use other elements as “fuels”. This results in the star starting to “swell”, becoming a red giant and releasing its outer layers to the interstellar medium. This occurs in one of the final stages of its life, the AGB phase (from  Asymptotic Giant Branch).

A multitude of chemical phenomena take place in the atmospheres of these evolved stars, enriched by successive material dredged-up. In principle, when we talk about the birth of dust grains, we mean precisely those atmospheres of evolved stars (also supernova explosions, which are much more massive stars, but this is another story).

The layers of material released by the AGB star and forming its atmosphere are composed of a huge amount of gas molecules and a small proportion of dust grains. We are interested to know how these grains of dust are formed, from what basic elements and under what physical conditions.

To understand this whole process it is important to know the chemical equilibrium in these atmospheres, that is, the state in which, although the chemical activity continues, the chemical composition remains stable. If we know the chemical equilibrium, we will know what atoms and molecules are at the origin of the formation of dust grains (which is what we are interested in). In addition, we will have the theoretical scenario with the sequence of the different types of grains that are expected to appear as matter flows and cools from the AGB star into the interstellar medium.

In our case, in the atmospheres of AGB stars, we know that the gas is at high temperature and pressure, which is very fortunate as these are the conditions under which it is valid to use chemical equilibrium. This would be very different if we talked about, for example, the interstellar medium, where temperatures and pressures are very small and the chemical composition is given by chemical kinetics. In that case, as Marcelino Agúndez (from our group Astromol in the Institute of Fundamental Physics, IFF-CSIC) states, “it would be necessary to know the constant kinetics of a large number of reactions, in those environments everything is rather more uncertain. The interest of applying chemical equilibrium to the atmospheres of AGB stars is that, in them, temperatures and pressures are high, ergo we can use chemical equilibrium and the chemical composition can be calculated in a simple way. This has been known since the 1970s.”.

And here we get into a paper recently published by a team of researchers from the Spanish Council for Scientific Research (CSIC), focused on studying the atmospheres of AGB stars (as we said before, medium-sized stars in the final stages of their  lives).

The idea was to update all the information available so, first of all, the team compiled and updated a large dataset of thermochemical properties for 919 gaseous and 185 condensed species involving 34 elements. The chemical composition in AGB star atmospheres was calculated thanks to a recently developed code. All available information obtained from astronomical observations was also updated to, as a last step, compare the predictions of the calculations with the observations. All with the idea of reviewing what we knew so far, what our successes and mistakes were, and future prospects about molecules, molecular aggregates, and solid condensates in the atmospheres of red giant stars.

Funambulist stars, what the equilibrium tells us

This study not only tells us which aggregates could act as “bricks” of dust grains construction (and  what may be the most likely gas precursors of these grains) but even throws information on what we do not find:  potentially detectable molecules that have not yet been observed have been identified, making them good candidates for detection with observatories such as ALMA.

Finally, there are also things that don’t fit: in some cases, theoretical analysis and data don’t match. In fact, there are discrepancies of several orders of magnitude for some molecules which are observed with abundances several orders of magnitude above the expectations from chemical equilibrium. This means that, in some areas of the stellar atmosphere, there are no chemical equilibrium conditions due to unidentified phenomena that could be related to ultraviolet photons or hydrodynamic processes.

What’s new thanks to the lab

To do this type of studies it is necessary to know the thermodynamic properties of each molecular species. In the case of the most common molecules, this data is known, but for the rarest ones it is necessary to calculate or measure them.

This study has incorporated, for the first time, the properties of a large number of molecular aggregates of titanium and carbon analyzed within the Nanocosmos (ERC) project in the laboratories of the Institute of Materials Science of Madrid (ICMM-CSIC). In carbon-rich AGB stars, forecasts say the first condensates would be carbon itself, titanium carbide (TiC) and silicon carbide (SiC). (In O-rich atmospheres, the first condensate expected is Al2OR3). And it was necessary to have data on these under-studied species in order to compare them with observations.

In short, this work tells us about our mistakes and successes, about the path on which these atoms and molecules pass, about the origins of dust grains and where they are expected to appear, about the agglomeration that initiates the formation of the first solid materials from a gas of atoms and small molecules.

We are interested in how its composition can influence what happens much later, when the birth cycle of a new star begins again with the condensation of those dust grains resulting in nuclear reactions. We will continue to build knowledge on this data, relegating the wrong ones and analyzing the new information, because that’s how science works.

More information:

Scientific paper:Chemical equilibrium in AGB atmospheres: Successes, failures and prospects for small molecules, clusters, and condensates“, M. Agúndez  (IFF-CSIC), J. I. Martínez  (ICMM-CSIC), P. L. de Andres (ICMM-CSIC), J. Cernicharo  (IFF-CSIC) and J. A. Martín-Gago (ICMM-CSIC).

But… what happens in those globules?

It is not the first time we talk about Orion, nor about the molecular cloud pierced by the winds of its most massive star… but this is about molecular globules. In this constant process of destruction, something is being created.

Gallery of globules detected at the edge of the expanding Orion bubble

Those who have ever read me (poor) will say that we always talk about the same areas of space. Legendary is the series about IRC+10216 (a star and its envelope, better known as CW Leonis) published on this platform, as well as studies related to the chemistry of Orion. This is because both are magnificent “laboratories” that we can observe with relative ease (translation: these places are “close” and bright enough to observe with our telescopes). The study of these areas is aided by new and increasingly precise instruments.

On this occasion, the combination of the IRAM 30 meters telescope (in Pico Veleta, Granada) and the SOFIA stratospheric telescope (which is mounted on an airplane), helped us to discover the presence of an extremely interesting phenomenon.

But let’s take perspective…  In the Orion Nebula there is a good mess. There are massive stars (of about 8 solar masses or more) being born and emitting winds and ultraviolet radiation, which, in turn, destroys the large molecular cloud in which they were born (the one that has provided them with the material and the necessary conditions to condense). In that scuffle, an international research team has detected the presence of small molecular globules.

Expanding gas bubbles – the result of the destruction of the parent cloud – form around young massive stars because wind and radiation violently “sweep” huge amounts of the material. Ultraviolet radiation is responsible for dissociating (destroying) the gas molecules. Similar shapes had previously been found around massive stars in the Milky Way, dozens of bubbles that were detected using infrared images (let’s not forget that those environments have lots of dust and that infrared makes it easy for us to “go through” the opaque outer layers and see what happens inside). The result of this whole process is that the rate of star birth slows down, as the amount of fuel available for the formation of new stars (the molecular gas) is limited.

But there is another consequence: the presence of small globules of molecular gas on the edge of these large expanding bubbles whose existence has been a surprise: “We did not expect this discovery: one does not expect the presence of molecular gas in this kind of environment so turbulent and “sterilized” by ultraviolet radiation, but we have detected a dozen globules of thick molecular gas that have survived these harsh conditions. Most of these globules can be transiting objects that eventually fade or evaporate. But we didn’t expect this script twist.”

This is said by one of the two researchers who has led this work, Javier R. Goicoechea, from the Astromol Group at the IFF-CSIC, who goes on to describe how they are: “The globules are not massive at all, their size is approximately 200 times smaller than the Orion Nebula itself and their typical mass is around a third of the mass of the Sun. That’s why we were surprised to find out what they were hiding.”

And what has been discovered inside those globules that seemed to be just lumps? Well, scientists have discovered that one of these globules is evolving to form a very young, low-mass star. Let’s say it would be the “daughter” of the one who is riding this whole mess (the young, “angry” star, the most massive in the Trapezium cluster, Orionis C, located at the center of the Orion Nebula).

The importance of the movement

To understand what was happening within the great Orion bubble there are several important parameters that until now had been difficult to obtain: knowing how it moves, what forces drive its expansion and what its chemical composition is. Thanks to the combination of the data obtained with these two facilities, the team has obtained the first images that solve the speed of the gas and show the properties of this bubble of 10 light years in size that is suffering the wrath of Orionis C, since the bubble expands at almost 50,000 km / h, providing its peculiar appearance to the iconic region that we know as “the sword of Orion”.

This information has been obtained thanks to the analysis of the emission of gases produced by molecules of carbon monoxide (CO) as well as positively charged carbon atoms (ionized carbon or C+, analyzed in the work led by Cornelia Pabst, of the University of Leiden, The Netherlands).

As the authors of these works state, “It is not yet clear whether these small objects can be a source of very low-mass stars, brown dwarfs, or planetary-mass objects. We have captured the first glimpses of the star-forming processes that are taking place within one of these small globules.”

The team hopes to be able to carry out more observations of the emission of other molecules (more sensitive to the presence of more dense gas inside the globules) to clarify their future and fate. Will they evaporate in the long run or, conversely, will they evolve into a nursery of newly formed stars?

Technical information:

This work is part of an international collaboration that leads two major complementary observation programs. One uses the 30-meter IRAM telescope in Pico Veleta, Spain (Dynamic and Radiative Feedback of Massive Stars, PI: J. R. Goicoechea) to map the emission of 12CO, 13CO and C18O (J=2-1) at a resolution of 11 arcseconds; the other uses NASA/DLR’s SOFIA airborne observatory (C+ Square-degree map of Orion, PI: Prof. A. G. G.M. Tielens) which has produced the largest map of the [CII]158 μm line (usually the brightest line in the neutral interstellar medium) at a resolution of 16 arcseconds. These Orion C+ images are also relevant as a local model in the extragalactic context as the ALMA and IRAM-NOEMA radiointerferometers can detect the emission of [CII] 158 μm from galaxies with very distant star formation (with high redshift).

The consortium consists of the following institutions: CSIC, University of Leiden, University of Cologne, IRAP-CNRS, IRAM, Max-Planck Institute for Radio Astronomy, ESAC, NASA Ames and University of Maryland.

The scientific articles related to this work are:

J. R. Goicoechea, C. H. M. Pabst, S. Kabanovic, M. G. Santa-Maria, N. Marcelino, A. G. G. M. Tielens, A. Hacar, O. Berné, C. Buchbender, S. Cuadrado, R. Higgins, C. Kramer, J. Stutzki, S. Suri, D. Teyssier, and M. Wolfire. Molecular globules in Orion’s Veil bubble. IRAM 30 m 12CO, 13CO, and C18O (2-1) expanded maps of Orion A. Accepted for publication in Astronomy & Astrophysics (2020).

– C. H. M. Pabst, J.R. Goicoechea, D. Teyssier, O. Berné, R.D. Higgins, E. T. Chambers, S. Kabanovic, R. Güsten, J. Stutzki, and A.G.G.M. Tielens: Expanding bubbles in Orion A: [CII]158μm observations of M42, M43, and NGC 1977. Accepted for publication in Astronomy & Astrophysics (2020).


Images of the Orion Nebula (M42). The left panel shows the emission of positively charged carbon atoms, observed with SOFIA, revealing a huge bubble pushed by the winds of the most massive star in the Trapezium cluster. The 12CO and 13CO images, taken with the 30-meter IRAM telescope, show the molecular gas in the cloud in which stars are forming, behind the bubble. The # numbers show the position of some of the detected globules at the edge of the bubble. Credits: Goicoechea et al. (2020).

Gallery of globules detected at the edge of the expanding Orion bubble. The reddish colors represent the emission of carbon monoxide molecules detected with the 30-meter IRAM telescope. The bluish color is an infrared image obtained by the Spitzer Space Telescope. The #1 globule coincides with the position of a very young, low-mass star. The white circle represents the angular resolution of the IRAM telescope 30-meters, approximately several times the size of the Solar System. Credits: Goicoechea et al. (2020).

Originally published in Spanish on the Naukas website: “Pero… ¿qué pasa en esos glóbulos?” (2020/07/02).

The Criegee intermediate-formic acid reaction explored by rotational spectroscopy

“The Criegee intermediate-formic acid reaction explored by rotational spectroscopy” is the title of the inside front cover paper recently published in the Journal “Physical Chemistry Chemical Physics” (PCCP) and whose authors are Carlos Cabezas (from our Astromol group) and Yasuki Endo.

Abstract: The atmospheric reaction of the simplest Criegee intermediate, CH2OO, with formic acid has been investigated in the gas phase by pulsed Fourier-transform microwave spectroscopy. The dominant nascent product from this reaction was identified as hydroperoxymethyl formate (HOOCH2OCHO), for which two different conformations, formed through independent insertion mechanisms, were observed in the discharged plasma of a CH2I2/O2/formic acid gas mixture. The conformational identifications are supported by the observation of 13C species in natural abundance together with the chemically mono substituted deuterium isotopologues. These isotopic observations further suggest that hydroperoxymethyl formate slightly decomposes, producing formic anhydride (OHCOCHO) in a dehydration reaction.

Link to the inside front cover

Link to the paper “The Criegee intermediate-formic acid reaction explored by rotational spectroscopy

L483 Trilogy (Part Three) – Where do you hide, Dicyanopolyyne?

Interstellar isocyanogen (CNCN) discovered

This is the third and final part of a trilogy in which we have unveiled several new molecules discovered in our L483 dark cloud. In the first part, it was the HSC and HCS isomers; in the second part, NCO; and today we close with the CNCN: that is, carbon everywhere.

It is true that interstellar chemistry is essentially organic. About three-quarters of the nearly 200 molecules detected to date in the interstellar and circumstellar medium contain at least one carbon atom. Among them there are alcohols, aldehydes, acids,  ethers and amines, but the most frequent functional group is that of nitriles, which contain a group of cyanide –CN. In fact, the strong bond of this group is present in more than 30 interstellar molecules, although, until recently, no molecule containing two cyano groups (dinitrile) had been observed in interstellar space.

We have already talked before about cyanogen (NCCN), that lethal gas for humans indirectly detected in our protagonist dark cloud, L483, in 2015 (see the article “Cyanogen: a poison, a comet and a jedi story”, where we talked about the protonated cyanogen, NCCNH+.) In this new study, the isocyanogen CNCN, which is a polar and metastable isomer of the cyanogen [1] has been detected for the first time in space (in the same cloud).  

The detection of CNCN in the interstellar medium reinforces the long-held idea that cyanogen is the main precursor to cyanide (CN) that has been observed for decades in many comets. In fact, recently the Rosetta mission  has detected cyanogen in comet 67P.

Cyanogen is the simplest member of the family of dicyanopolyynes, consisting of a highly unsaturated linear skeleton of carbon atoms topped by a cyano group at each end, i.e., N≡C−(C≡C)n−C≡N. They are stable molecules and the authors of this work that closes our L483 trilogy have deduced that, in interstellar clouds, these molecules with two cyano groups (such as NCCN) are probably as abundant as molecules with a single group –CN  (as HCN)  [2].

And why do we have to go around deducting? Can’t we see them directly? Well, that’s the point. The problem in detecting certain species in the interstellar medium (among them, the dicyanopolyynes) is that they do not leave “footprint” because they are not  polar.

As we said in the second part of this trilogy, the more polar a molecule is, the more intense the lines. Therefore, if a molecule has low polarity the lines will become weaker and detecting them will be more complicated.

In this particular case everything is even more complicated, since there is no way to detect the dicyanopolyynes because they are totally apolar. Therefore, having no rotational spectrum, it cannot be observed by radioastronomical techniques. But there are other ways to deduce their presence.

For example: in the carbon-rich envelope IRC+10216 (which we have also talked about a lot for its diva complex), the presence of NCCP – a chemical cousin of the cyanogen in which an atom of N is replaced by an atom of P – was tentatively identified. Therefore, it is reasonable to think (although we cannot observe them) that the dicyanopolyynes can be abundant in molecular clouds.

To investigate the plausibility of this hypothesis, it was proposed that the presence of NCCN in interstellar and circumstellar clouds can be indirectly tested through the observation of chemically related polar molecules, a hypothesis that has been confirmed with the detection a few years ago of protonated cyanogen (NCCNH+) and the discovery of the new member of the family, CNCN.

The isocyanogen CNCN

At this point in our trilogy, we see that, to deduce the presence of a molecule indirectly, we have to use a multitude of tools: chemical models that we are perfecting, better detectors and instruments in our radio telescopes and, therefore, more sensitive observations of the areas we are studying.

While the presence of NCCN in interstellar clouds seems undoubted due to the detection of NCCNH+ and CNCN, their abundance remains difficult to define due to the little knowledge about the chemistry that relates to these species. To further know the chemistry of dicyanopolyynes in space it will be necessary to carry out experiments and theoretical studies of some key reactions, in addition to astronomical observations of high sensitivity. It seems we have to keep looking at and interpreting the data from these regions.

Concerning the dark cloud L483, it has revealed some of its secrets in the survey that has given rise to this trilogy, based on several scientific publications with associated discoveries that are cementing a path on which to continue asking us, if it does, “Where do you hide, dicyanopolyyne?”.


[1] It has also been tentatively discovered in TMC-1, the taurus molecular cloud.

[2] It is estimated that the abundance of NCCN in relationto H2 may be of the order of between 10−9–10−7, similar to that of HCN.

More information:

Discovery of Interstellar Isocyanogen (CNCN): Further Evidence that Dicyanopolyynes Are Abundant in Space“. M. Agúndez, N. Marcelino and J. Cernicharo (Institute of Fundamental Physics, CSIC, Spain).

A sensitive λ 3 mm line survey of L483. A broad view of the chemical composition of a core around a Class 0 object“. M. Agúndez, N. Marcelino and J. Cernicharo (Institute of Fundamental Physics, CSIC, Spain), E. Roueff (Paris Observatory, Sorbonne University, PSL University, CNRS, LERMA 2), and M. Tafalla (National Astronomical Observatory, OAN-IGN, Spain).

Based on observations carried out with the IRAM 30 m radio antenna.

Image: Image of the L483 region captured by NASA’s Spitzer Space Telescope. The circle points the area studied with the IRAM 30m radio telescope and published in the article “A sensitive λ 3 mm line survey of L483. A broad view of the chemical composition of a core around a Class 0 object’.

Originally published in Spanish on the Naukas website: “¿Dónde te escondes, dicianopoliino? Trilogía de L483 (Tercera parte)“. (2019/07/22).

L483 trilogy (Part Two) – Put a radical in your dark cloud

Detection of the NCO radical in space

This is what the L483 dark cloud looks like if we don’t use radio astronomy

In the first part of this series we talked about the sulfur lost in L483. But in the studies carried out in this dark cloud, much more has been discovered. Among them, the first detection in space of the isocyanate radical (NCO) with a significant abundance.

Studying the observations of L483 carried out with the IRAM 30m radio telescope, it was seen that there were bright carbon chains such as C4H, which suggested that the region could host a propitious environment to carbon chain chemistry [1].

Why are carbon chains important? Most molecules observed in space can be formed only with atoms of hydrogen (H), carbon (C), nitrogen (N) and oxygen (O). These atoms are the pieces for building organic and prebiotic molecules and, together, constitute the backbone of the peptide bond that binds two amino acids and allows the construction of long proteins. Therefore, the observation of simple molecules with the C(=O)–N group in space can provide important clues about the first chemical steps in amino acid synthesis, considered key in all biological processes.

The isocyanate radical precisely consists of a C(=O)–N structure and is therefore the simplest molecule that houses the base scheme of the peptide bond. It has efficient formation mechanisms but, although it is predicted (from what the models tell us) that it must be abundant in dark clouds… its abundance is small, which complicates its detection. In addition, it has a low polarity (the higher the polarity, the more intense the lines of the molecule) [2] so the observed lines are weak. To this must be added the “noise” (which will depend on the observation time and the sensitivity of the instrument).

We usually use the metaphor of the field of grass that does not let you see the flowers: our field of herbs (the noise) will be reduced the higher the quality and sensitivity of our observations, letting us distinguish the “flowers”, which would be the lines of the molecules.

Technological advances are enabling us to make progress in this direction. Increasingly sensitive detectors are being built, which makes the noise less. In addition, in this work a deep survey has been carried out that has allowed us to observe in more detail, providing many unexpected results (which we will continue to talk about in the third part of this trilogy, what did you think, that we were going to tell you at once? Well, no).

How the NCO is formed

When talking about “zones” or regions in a certain environment of space, we must clarify that there is no uniformity in the conditions that give rise to the chemistry of these places. In fact, recent observations carried out with the ALMA interferometer  have demonstrated a chemical differentiation in L483, which has carbon chains such as C2H that trace the envelope, and more complex organic compounds distributed around the protostar, that is, in these two areas different physical and chemical phenomena are occurring that give rise to a different chemical richness.

The detection of NCO (carried out with IRAM 30m) has taken place in the envelope of the low mass protostar in L483, and with this information it follows that the chemical processes for the formation of NCO are mainly two: one is from the reaction between CN and O2 and another would be by the recombination of the ion H2NCO+, which has also been detected in this work, thus supporting the formation of NCO by this route.

One of the important aspects of taking steps in the discoveries of new molecules is that the chemical models are updated, in this case, those related to NCO: taking into account the uncertainties in the model, the observed abundances are reproduced relatively well, which indicates that we are on the right track.

But there is still much to study. Although the survey has been of incredible sensitivity, “The next step -says Nuria Marcelino, lead author of this paper- would be to carry out NCO observations on sources that are at different stages of the star formation process. This could help us understand its role in the prebiotic chemistry of space.”

With this survey –she continues– we have revealed the chemical richness of L483, discovering several species that had not been detected before and confirming others that had been detected tentatively. Finally, we have been able to see the flowers among the grass.”

But, friends, there are still many flowers to be revealed. We’ll look at some of them in the next part of this L483 trilogy.


[1] Apart from carbon chains, L483 is also rich in oxygen-carrying organic molecules    such as HCO, HCCO, H2CCO, CH3CHO, HCCCHO and c-C3H2O.

[2] Polarity has to do with the distribution of the electric charge in the molecule. The more asymmetric the charge distribution, the more polar the molecule. The main implication of this is that, the more polar a molecule is, the more intense the lines. Therefore, as far as the NCO is concerned, the low polarity makes the lines weak, making it difficult to detect them.

More information:

This work has been published in the paper Discovery of the elusive radical NCO and confirmation of H2NCO+ in space“, A&A 612,L10  (2018). By N. Marcelino, M. Agúndez, J. Cernicharo (Instituteof FundamentalPhysics, CSIC, Spain), E. Roueff (Sorbonne University, Paris Observatory, CNRS, France) and M. Tafalla, (National Astronomical Observatory, IGN, Spain). Based on observations carried out with the IRAM 30m radio telescope.

Image: This is what the L483 dark cloud looks like if we don’t use radio astronomy. Credit:  NRAO/Gary Fuller.

Originally published in Spanish on the Naukas website: “Pon un radical en tu nube oscura. Trilogía de L483 (Segunda parte)” (2019/06/26).

L483 trilogy (Part One) – In Search of Lost Sulphur

First identification of two species in space, HCS and HSC

Image of the L483 region captured by NASA’s Spitzer Space Telescope

Over the past few decades, various research teams working to study different areas of space have had the same question: where is the missing sulfur? This is what happens, for example, with the study of some protoplanetary disks  and interstellar clouds. That is because sulfur chemistry outside the Earth, especially in the dark and cold clouds, on which we will focus today, presents some unknowns such as the detection of less sulfur than expected.

Sulfur in the gas phase can be found as part of different molecules (called sulfur “carrier” species).  However, these species are less than 0.1% of the estimated cosmic abundance of sulfur for dark clouds, that is, only a tiny amount of what is supposed to be there has been detected.

The case of HCS and HSC in the cold cloud L483

The team led by Marcelino Agúndez, Ramón y Cajal researcher at the Institute of Fundamental Physics of the CSIC, who is among those looking for “lost sulfur”, detected two new molecules carrying sulfur: the HCS radical and its less stable isomer, HSC. They identified them in the dense cloud L483, a source with a very rich chemistry and where new molecules from other families (such as  HCCO, NCCNH+ and  NS+) have also been discovered.  

L483 is a molecular cloud, located in the Aquila Rift, which houses the IRAS 18148-0440 protostar. This protostar is in full transition, going from being a protostar of class 0 to class I, that is, the dust and gas around it are taking the form of a disk and begin to distinguish its layers (although it does not yet have reactions in the core, that will come after going through phases II and III, after which it will end up being a full-right star).

The presence of the protostar in L483 involves a great deal of activity, with material from the cloud falling by gravity on it, fattening it, as well as a powerful jet of matter emanating from it, taking away much of the angular momentum and favoring the process of star formation. Given the environment, there should be a lot of sulfur, so it must be identified among the observations’ data.

The sulfur molecules discovered, HCS and HSC, are not abundant enough to explain the problem of lost sulfur, but their detection has revealed several peculiarities about how sulfur chemistry works in interstellar clouds. Since sulfur is in the same column of the periodic table as oxygen, both elements are considered to have similar chemical properties. However, the detection of HCS and HSC has revealed that sulfur and oxygen chemistry behave significantly differently than expected. Let’s see why.

To understand this we can compare the abundances of sulfur molecules with those of their oxygen analogues. That is, if we talk about the molecule with hydrogen, carbon and sulfur (HCS), its analog with oxygen is HCO (hydrogen, carbon and oxygen). In this way we can compare the relative abundances of the species carrying sulfur H2CS /HCS (being H2CS the stable form and HCS the unstable radical) with the relative amounts of H2CO /HCO.

The result is that in L483, H2CO (formaldehyde) is ten times more abundant than HCO (formyl radical). But in the case of its sulfur analogue the same does not happen, since H2CS (Thioformaldehyde) is as abundant as HCS. In addition, in L483 HCS is even more abundant than HCO, which is surprising, given that oxygen is more abundant than sulfur in the cosmos.

On the other hand, the metastable isomer HSC is found with a low abundance, while its oxygen analogue HOC has not yet been observed in space, mainly because there is a total lack of experimental information about this species (it has not been possible to characterize it in laboratory experiments).

Delving a little into the title of this report, we wonder, again, where is the sulfur that we don’t see. It is interesting to note a recent study, by Vidal et al., “On the reservoir of sulphur in dark clouds: chemistry and elemental abundance reconciled“, which    concludes that most of the sulfur in dark cold clouds should be in the form of H2S and SH ice on the surface of dust grains.

This study also indicated that, to detect HCS in gas phase, it would be necessary more than a thousand hours of observation with the IRAM 30 m telescope, concluding that it was difficult to locate HCS in gas phase in dark and cold clouds. However, this work, in the words of Agúndez, “shows that, although there are many unknowns to be solved, we have managed to detect the presence of HCS with much fewer hours of observation“.

Then, where is the sulfur missing from the dark, cold clouds? It is possible that sulfur is deposited only on dust grains, although it is not clear how.  Part of it could get trapped in the core of the grains as refractory compounds and another part could be in the form of ice. Although it is also possible that molecules of the gas phase that have not yet been identified may contain a significant amount of sulfur. It may even be in atomic form.

So, we assume that sulfur is there, but we haven’t been able to detect it yet with our instruments. On the other hand, studies of this region have not only revealed its “lack” of sulfur… but that will be in the next chapter of this trilogy about L483, the dark cloud that has so many things to reveal about the chemical complexity of the universe.

More information:

This work has been published in the paper “Detection of interstellar HCS and its metastable isomer HSC: new pieces in the puzzle of sulfur chemistry”,  A&A 611, L1 (2018). By M. Agúndez, N. Marcelino, J. Cernicharo  (Institute of Fundamental Physics, CSIC, Spain)  and M. Tafalla, (Observatorio Astronómico Nacional, IGN, Spain). Based on observations carried out with the IRAM 30m Telescope.

IMAGE: Image of the L483 region captured by NASA’s Spitzer Space Telescope.

Originally published in Spanish on the Naukas website: “En busca del azufre perdido. Trilogía de L483 (Primera parte)” (2019/06/18).