Rémi Bérard, New Nanocosmos Doctor

On Monday 23rd of September, Rémi Bérard (center of the picture) presented his PhD thesis entitled Formation and growth by plasma of laboratory stardust analogues : investigation of the role of the c/o ratio and metals”, that was carried out at the IRAP in the framework of the Nanocosmos projet under the direction of Kremena Makasheva (LAPLACE, right side of the picture) and Christine Joblin (IRAP, on the left).


Summary :

Dust formation is a fundamental topic in both cold plasma physics and astrophysics. This PhD thesis, carried out at the interface between the two fields, aims to better understand the formation of stardust. The problem is treated experimentally in cold plasmas and discussed in the context of the environment of evolved stars.

We observe the formation of successive generations of dust due to pulsed injection of hexamethyldisiloxane (HMDSO: Si2O(CH3)3) in a capacitively-coupled radiofrequency asymmetric plasma sustained in argon. The used molecular precursor contains potential stardust forming elements, like carbon, oxygen, silicon and hydrogen. Our approach involves different steps: study of the dust formation in the plasma, dust collection, characterization of the dust properties and correlation of the plasma parameters with the dust characteristics. We have thus succeeded to identify optimum conditions for the formation of organosilicon dust with typical size of 50 nm.

A major factor impacting dust formation in evolved stars is the variation of the C/O ratio, which is though to determine two large families of stardust, silicates (C/O < 1) and carbonaceous dust (C/O > 1). To explore this effect, we have enriched the Ar/HMDSO mixture with oxygen aiming at a variation of the C/O ratio in the plasma. Above a certain quantity of oxygen, dust is not formed anymore in the plasma. The abundance of oxygen limits dust formation through inhibition of the dust seeds in the gas phase. Instead, deposition of a silica- like matrix is favored.

The role of metals is studied through sputtering of a silver target during organosilicon dust formation. We have demonstrated the formation of dust with composite structure in this case. Dust contains crystalline silver nanoparticles that attach to the amorphous organosilicon dust during their growth phase. Moreover, the presence of silver leads to a large variety of molecules composed of species containing Ag and/or Si and hydrocarbon species. Those molecules reveal a complex chemistry around three competitive processes at molecular scale: dust formation involving molecules such as SiCH3 or SiOCH3, metallic grains with clusters of Agn and aromatic molecules of large size such as C16H10 and C24H12, whose formation path involves radicals and possibly an organometallic chemistry as revealed by AgC5H6 and AgC13H8. The above results demonstrate the undoubted necessity to tackle stardust formation by taking into account the chemical complexity of these media.

Elegant and fast: the GACELA is running

The Gas Cell chamber

On June 7, 2019, a first paper on the GACELA (GAs CEll for Laboratory Astrophysics) experimental set-up is out at the “Astronomy & Astrophysics” journal (A&A, volume 626, A34, 2019).

More than 3 years have elapsed since the first designs were envisaged for this set-up. Finally, at the end of 2017, the chamber (see figure above) was delivered and successfully tested against leaks. On the other hand, the GACELA broad-band radio receivers (Q and W bands, 31.5–50 and 72–116.5 GHz, respectively) were successfully commissioned in the second semester of 2017 and interfaced with the GACELA set-up in February 2018. Several experimental runs were performed, showing high quality signal-to-noise ratio spectra of molecular species (CH3CN, CH3OH, CH4/N2, CH4/N2/CH3CN, etc).

As stated by the authors, GACELA has achieved an important milestone. It is the first time that we can observe the thermal emission of molecules with an instantaneous band width of 20 GHz in Q band and 3 × 20 GHz in W band for Laboratory Astrophysics. These rotational spectroscopy measurements are complemented by mass spectrometry and optical spectroscopy.

In summary, NANOCOSMOS has developed an elegant and fast-responding set-up, the GACELA, to provide high-resolution and high-sensitivity spectra of molecular species produced in cold plasmas or UV experiments.

More information:

This research was presented in the paper “Broad-band high-resolution rotational spectroscopy for laboratory astrophysics“, published in Astronomy and Astrophysics 626, A34 (29pp), 2019 June 7. The authors are: José Cernicharo (Instituto de Física Fundamental, IFF-CSIC), Juan D. Gallego (Centro de Desarrollos Tecnológicos, Observatorio de Yebes, IGN), José A. López-Pérez (CDT, OY, IGN), Félix Tercero (CDT, OY, IGN), Isabel Tanarro (Instituto de Estructura de la Materia, IEM-CSIC), Francisco Beltrán (CDT, OY, IGN), Pablo de Vicente (CDT, OY, IGN), Koen Lauwaet (Instituto de Ciencia de Materiales de Madrid, ICMM-CSIC & IMDEA Nanociencia), Belén Alemán (ICMM-CSIC & IMDEA Materiales), Elena Moreno (IFF-CSIC), Víctor J. Herrero (IEM-CSIC), José L. Doménech (IEM-CSIC), Sandra I. Ramírez (Centro de Investigaciones Químicas, UAEM, Mexico), Celina Bermúdez (IFF-CSIC), Ramón J. Peláez (IEM-CSIC), María Patino-Esteban (CDT, OY, IGN), Isaac López-Fernández (CDT, OY, IGN), Sonia García-Álvaro (CDT, OY, IGN), Pablo García-Carreño (CDT, OY, IGN), Carlos Cabezas (IFF-CSIC), Inmaculada Malo (CDT, OY, IGN), Ricardo Amils (CDT, OY, IGN), Jesús Sobrado (Centro de Astrobiología, INTA-CSIC), Carmen Díez-González (CDT, OY, IGN), José M. Hernández (IFF-CSIC/CDT, OY, IGN), Belén Tercero (CDT, OY, IGN), Gonzalo Santoro (ICMM-CSIC), Lidia Martínez (ICMM-CSIC), Marcelo Castellanos (IFF-CSIC), Beatriz Vaquero-Jiménez (CDT, OY, IGN), Juan R. Pardo (IFF-CSIC), Laura Barbas (CDT, OY, IGN), José A. López-Fernández (CDT, OY, IGN), Beatriz Aja (Universidad de Cantabria), Arnulf Leuther (Fraunhofer Institut fur Angewandte Festkorperphysik, Germany), José A. Martín-Gago (ICMM-CSIC).

The GACELA experimental set-up is located at the Centro de Desarrollos Tecnológicos, Observatorio de Yebes, thanks to a bilateral agreement between CSIC and IGN for the development of the NANOCOSMOS project.

Supplementary Cover of the JACS

Members of the Nanocosmos team from the ICMM-Madrid (ESISNA Group of the Institute of Material Science of Madrid), together with other researchers, have published an interesting paper in the JACS, Journal of the American Chemical Society: Atomic hydrogen makes the difference. The supply of atomic hydrogen during the on-surface annealing of PAHs substantially favors the formation of intermolecular covalent C–C bonds. The reason resides in the radical-like intermediate formed as a consequence of molecular super-hydrogenation.

Read more about those interesting results in the paper “On-Surface Hydrogen-Induced Covalent Coupling of Polycyclic Aromatic Hydrocarbons via a Superhydrogenated Intermediate“, one of the Supplementary Cover Art for the Journal of the American Chemical Society (February 27, 2019).

Here is the link to the website and the link to the paper. Congratulations to the team!

Supplementary Cover Art for the manuscript: On-Surface Hydrogen-Induced Covalent Coupling of Polycyclic (10.1021/jacs.8b12239) published in Journal of the American Chemical Society.

The benzylium and tropylium cations identified as two stable C7H7+ isomers

The picture, which is a cover of the journal ChemPhysChem, schematizes the production of the C7H7 ion by dissociative ionization of toluene and the identification, by infrared spectroscopy, of the two isomers produced: the cations benzylium (right) and tropylium (left).

Experiments driven by an international team involving the Institute for Research in Astrophysics and Planetary Sciences (IRAP, Université de Toulouse/CNRS) and the Laboratory of Quantum Chemistry and Physics (LCPQ, Université de Toulouse/CNRS), enabled to identify the two stable isomers of C7H7+ ion.

The ion C7H7is a well-known species in mass spectrometry, formed by ionization of hydrocarbons such as toluene. The two most stable structures proposed for this ion are benzylium and tropylium ions. The first (a benzene with a methylene group) could be identified by its chemical reactivity, but is not the case of the second, whose structure consisting of an aromatic cycle of 7 carbons is predicted by quantum chemistry calculations.

Two structures have been identified for C7H7+ and the vibrational spectra obtained are in agreement with those of benzylium and tropylium ions calculated with the density functional theory. In addition, measures in depletion helped to show that no other isomer was present and this for different precursors used in the production of C7H7+.

The study took advantage of the FELion line, installed on the free electron laser FELIX, in the Netherlands. FELion includes a cryogenic ion trap that allows attaching an atom of rare gas on the ions studied. This technique of tagging allows to implement a spectroscopy of action by dissociating the complexion/atom of rare gas with a single infrared photon unlike the technique usually used of multiple absorption of photons to attain the threshold of dissociation of the ion. This technique has the advantage to probe ions without heating them and so without disrupting their structure through processes of isomerization.

This work of identification of C7H7+ isomers opens up prospects for the study of the growth paths of the hydrocarbon ions in complex environments both on Earth (chemistry of flames, and plasmas) or space (interstellar chemistry and planetary atmospheres as Titan’s).

This interdisciplinary work (INSU/INP/INC) has been initiated as part of the ERC Synergy NANOCOSMOS project in collaboration with the CSIC (Madrid) and involves a collaboration between the universities of Toulouse and Cologne as part of the European Training Network (ETN) EUROPAH.

Scientific paper: 

P. Jusko, A. Simon, S.Banhatti, S. Brünken, C. Joblin (2018) DirectEvidence of the Benzylium and Tropylium Cations as the two long-lived Isomersof C7H7+, ChemPhysChem, doi:10.1002/cphc.201800744 – Archives ouvertes: hal-01880438, arXiv:1809.09375

Link to the INSU news page: Les cations de benzylium et tropylium identifiés comme les deux isomères stables de C7H7+


New Nanocosmos Doctor

Some news from the young team surrounding our PI from Toulouse, Christine Joblin. Sarah Rodríguez Castillo (third on the left, first row) presented on October 30th 2018 her PhD thesis entitled “Study on the dissociation of astro-PAHs”, that was carried out at the University of Toulouse/CNRS in the framework of the Nanocosmos projet.

Congratulations on this great achievement, Doctor!


Polycyclic Aromatic Hydrocarbons (PAHs) are revealed in astrophysical environments thanks to their characteristic infrared emission after these molecules are subjected to the vacuum ultraviolet (VUV) radiation from nearby massive stars. This interaction regulates their charge state, stability and dissociation mechanisms, which in turn affect the energy balance and the chemistry of the gas in the interstellar medium. In particular, PAHs could contribute to the formation of the most abundant molecule, H2, in photodissociation regions (PDRs). This work aims at contributing to these topics by quantifying the VUV photoprocessing of specific medium-sized PAH cations through experimental studies complemented by computational investigations.The experimental results were gathered from two campaigns at synchrotron facilities: ion trap experiments allowed us to obtain the yields of ionization and fragmentation and the branching ratios between the different photoevents, while from iPEPICO spectroscopy we obtained breakdown curves and RRKM-fitted dissociation rates. We detail the case of the fragmentation processes of two isomers of dibenzopyrene cation (C24H14+) in order to assess the impact of structure on these processes. We present Density Functional Theory calculations and Molecular Dynamics simulations, which evidence the relevance of structure and planarity in these mechanisms and provide a better view on the dissociation pathways and energetics.This work brings significant new data for models that describe the chemical evolution of PAHs in astrophysical environments, including the first measurement of the ionization yield of medium-sized PAH cations as well as several dissociation rates. We also report a new mechanism, involving specific structures with bay areas, that would need to be considered while evaluating the contribution of PAHs to the formation of H2 in PDRs.