Actividades i-link

i-link Activities

Group Metting on-line (23rd March, 2021)

Attendants: Marta Hernández, Tomas González, Massimiliano Bartolomei, José Campos, Lukas Tiefenthaler, Florent Calvo, Nadine Halbserstad, Elizabeth Gruber, Paul Scheier, Siegfried Kollatzek, Eva María Zunzunegui.

Visits

University of Innsbruck (19th-24th September, 2021)

José Campos Martínez
Marta I. Hernández

CNRS- University of Toulouse (30th November, 4th December, 2021)

Marta I. Hernández
Massimiliano Bartolomei
Esther García-Arroyo

LCAR Seminar

Marta I. Hernández

“Microscopic processes for hydrogen chemisorbed on graphene: permeation and recombination”.

Hydrogenated graphene is of great interest in several different fields such as hydrogen technologies, astrochemistry, nuclear fusion, electronics and magnetism. Using large molecular prototypes of graphene, we have carried out density functional theory computations to study in detail two processes occurring in this system, namely, the permeation or flipping of chemisorbed hydrogen atoms through graphene and the recombination of these atoms (desorption leading to the formation of hydrogen molecules), which can be regarded as the subsequent step after permeation. Firstly, we will present a new mechanism for the flipping of chemisorbed hydrogen atoms1 or protons2 through a graphene layer (see figure), where we have found that the activation energies involved are of the order of recent experimental findings 3,4. In addition, we will show preliminary results on reaction paths and rate coefficients for the recombination of hydrogen and deuterium, which exhibit large isotopic substitution effects (due to zero-point energy and tunneling) in qualitative agreement with thermal desorption measurements5,6. We believe that these studies will help to rationalize the experimental results as well as to provide some clues about properties of hydrogenated graphene.

[1] M. Bartolomei, M. I. Hernández, J. Campos-Martínez, R. Hernández-Lamoneda, G. Giorgi, “Permeation of chemisorbed hydrogen through graphene: a flipping mechanism elucidated”, Carbon 2021, 178, 718
[2] M. Bartolomei, M. I. Hernández, J. Campos-Martínez, R. Hernández-Lamoneda, “Graphene multi-protonation: A cooperative mechanism for proton permeation”, Carbon 2019, 144, 724.
[3] S. Hu et al, “Proton transport through one-atom-thick crystals”, Nature 2014, 516, 227.
[4] P. Z. Sun et al, “Limits on gas impermeability of graphene”, Nature 2020, 579, 229
[5] T. Zecho et al, “Adsorption of hydrogen and deuterium atoms on the (0001) graphite surface”, J. Chem. Phys. 117, 8486 (2002)
[6] L. Hornekaer et al, “Metastable structures and recombination pathways for atomic hydrogen on the graphite (0001) surface”, Phys. Rev. Lett. 96, 156104 (2006)

 

Theory Group Meeting Talks:

Massimiliano Bartolomei

“Ab initio results for H2 molecules adsorbed on Naphthalene doped with Na atoms”

Esther García-Arroyo

“Transmission of hydrogen isotopes through a graphdiyne layer”

 

Madrid (February, 13th, 2022)

Siegfried Kollatzek (from University of Innsbruck, Austria).

Seminar at IFF

Sala de conferencias, C/ Serrano 121
Miercoles 16 de marzo de 2022 a las 12:00

HOW TO DOPE HIGHLY CHARGED HELIUM NANO DROPLETS
Siegfried Kollotzek
Institute for Ion Physics and Applied Physics,
University of Innsbruck, Austria

Building on our recent report [1] on the production of stable, highly charged droplets of superfluid helium, a new experimental method [2] was designed to investigate chemical and physical cluster processes in the sub-kelvin environment with a high ion yield. Properties of clusters often depend critically on the exact number of atomic or molecular building blocks, however, most methods of cluster formation lead to a broad size distribution and cluster intensity anomalies often designated as magic numbers. Here we present a novel approach of breeding narrowly size selected clusters via pickup of dopants into multiply-charged helium nanodroplets (A). We also demonstrate a method of softly ionizing dopant molecules by proton transfer [3], while largely preventing fragmentation, even for notoriously delicate molecules (B).  Finally, recent measurements indicate promising results while studying the influence of sodium atoms doped onto PAH’s on their ability to reversible attach H2 molecules (C).

References:
[1] F. Laimer et al Phys. Rev. Lett. 123, 165301 (2019)
[2] L. Tiefenthaler et al. Rev. Sci. Instrum. 91, 033315 (2020)
[3] L. Tiefenthaler and S. Kollotzek et al. Phys. Chem. Chem. Phys. 22, 28165-28172 (2020)

 

 

Madrid (October, 16th-20th, 2022)

Nadine Halberstadt

Laboratoire des collisions, Agrégats et Réactivité,
CNRS/University of Toulouse 3, France

 

Madrid (October, 18th-20th, 2022)

Ernesto García Alfonso

Laboratoire des collisions, Agrégats et Réactivité,
CNRS/University of Toulouse 3, France

 

Intermol Group Meeting Talks:

Ernesto García Alfonso

“Coulomb explosion of alkali dimers on helium droplets. Is really the triplet state dominant?”

Seminar at IFF

Sala de conferencias, C/ Serrano 121
Miercoles, 19 de octubre 2022 a las 12:00

CLUSTERING DYNAMICS IN SUPERFLUID HELIUM
NANODROPLETS: A THEORETICAL STUDY

Nadine Halberstadt

 

Helium nanodroplets are intriguing, quantum fluid objects of finite size (thousands to billions of 4He atoms). Their properties include superfluidity, very low temperature Image (0.38 K), high energy dissipation rate, quantum vortices,…. In a pioneering experiment, the Vilesov’s group used Ag, Ar or Xe atom doping to visualize quantum vortices, which resulted in the formation of filament-shaped clusters along the vortex lines.
I will present recent theoretical studies on the collision of heliophilic atoms with a droplet, followed by their solvation and clustering, obtained in collaboration with M. Barranco and M. Pi (University of Barcelona). The goal is to investigate the specificities of the solvatation and the clustering processes in this superfluid environment, and the role of vortices.
The simulations use the Helium density functional theory (4He-DFT) and its time-dependent version (4He-TDDFT), which have proven to be the best compromise between accuracy and feasibility to study the stability and real time dynamics of doped helium droplets with a size comparable to experiments. They reproduce the attractivity of dopant atoms to the vortex lines, with rather surprising final cluster configurations, very different from the gas phase ones.

 

CNRS-University Grenoble-Alpes (November, 13th-15th, 2022 )

José Campos Martínez
Marta I. Hernández

 

University of Innsbruck (November, 21st-24th, 2022)

Tomás González Lezana
Massimiliano Bartolomei

 

PUBLICATIONS

Helium nanodroplets as an efficient tool to investigate hydrogen attachment to alkali cations. Siegfried Kollotzek, José Campos-Martínez, Massimiliano Bartolomei, Fernando Pirani, Lukas Tiefenthaler, Marta I. Hernández, Teresa Lázaro, Eva Zunzunegui-Bru, Tomás GonzálezLezana, José Bretón, Javier Hernández-Rojas, Olof Echt and Paul Scheier. Phys. Chem. Chem Phys. xx , xxx-xxx (2022).
DOI: 10.1039/10.1039/D2CP03841B .

We report a novel method to reversibly attach and detach hydrogen molecules to positively charged sodium clusters formed inside a helium nanodroplet host matrix. It is based in the controlled production of multiply charged helium droplets which after the pick up of sodium atoms and exposition to H2 vapor, lead to the formation of Na+m(H2)n clusters, whose population is accurately measured by a time of flight mass spectrometer. The mass spectra reveal specially favorable Na+(H2)n and Na+2(H2)n clusters for specific “magic” numbers of attached hydrogen molecules. Energies and structures of these clusters have been investigated by means of quantum-mechanical calculations employing analytical interaction potentials based on ab initio electronic structure calculations. A remarkable agreement is found between the experimental and the theoretical magic numbers.

 

links of interest

https://ec.europa.eu/research/mariecurieactions/

https://ec.europa.eu/research/mariecurieactions/calls/msca-doctoral-networks-2021