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).

Gas phase Elemental abundances in Molecular cloudS (GEMS): III. Unlocking the CS chemistry: the CS plus O reaction

Authors: Bulut, N.; Roncero, O.; Aguado, A.; Loison, J-C; Navarro-Almaida, D.; Wakelam, V; Fuente, A.; Roueff, E.; Le Gal, R.; Caselli, P.; Gerin, M.; Hickson, K. M.; Spezzano, S.; Riviere-Marichalar, P.; Alonso-Albi, T.; Bachiller, R.; Jimenez-Serra, I; Kramer, C.; Tercero, B.; Rodriguez-Baras, M.; Garcia-Burillo, S.; Goicoechea, J. R.; Trevino-Morales, S. P.; Esplugues, G.; Cazaux, S.; Commercon, B.; Laas, J.; Kirk, J.; Lattanzi, V; Martin-Domenech, R.; Munoz-Caro, G.; Pineda, J.; Ward-Thompson, D.; Tafalla, M.; Marcelino, N.; Malinen, J.; Friesen, R.; Giuliano, B. M.; Agundez, M.; Hacar, A.

Contribution: Article


Publication date: 2021/02/02

DOI: 10.1051/0004-6361/202039611