i-link Activities

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.


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

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).

[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


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




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. 24 , 462-470 (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.

Attachment of Hydrogen Molecules to Atomic Ions (Na+, Cl): Examination of an Adiabatic Separation of the H2 Rotational MotionEsther García-ArroyoJosé Campos-MartínezMassimiliano BartolomeiMarta I. HernándezFernando Pirani, ChemPhysChem. 24, e202300424 (2023).

DOI: 10.1002/cphc.202300424.

Interactions between molecular hydrogen and ions are of interest in cluster science, astrochemistry and hydrogen storage. In dynamical simulations, H2 molecules are usually modelled as point particles, an approximation that can fail for anisotropic interactions. Here, we apply an adiabatic separation of the H2 rotational motion to build effective pseudoatom-ion potentials and in turn study the properties of (H2)nNa+/Cl clusters. These interaction potentials are based on high-level ab initio calculations and Improved Lennard-Jones parametrizations, while the subsequent dynamics has been performed by quantum Monte Carlo calculations. By comparisons with simulations explicitly describing the molecular rotations, it is concluded that the present adiabatic model is very adequate. Interestingly, we find differences in the cluster stabilities and coordination shells depending on the spin isomer considered (para- or ortho-H2), especially for the anionic clusters.


Solvation of cationic copper clusters in molecular hydrogen. 


Multiply charged superfluid helium nanodroplets are utilized to facilitate the growth of cationic copper clusters (Cun+, where n = 1–8) that are subsequently solvated with up to 50 H2 molecules. Production of both pristine and protonated cationic Cu clusters are detected mass spectrometrically. A joint effort between experiment and theory allows us to understand the nature of the interactions determining the bonding between pristine and protonated Cu+ and Cu2+ cations and molecular hydrogen. The analysis reveals that in all investigated cationic clusters, the primary solvation shell predominantly exhibits a covalent bonding character, which gradually decreases in strength, while for the subsequent shells an exclusive non-covalent behaviour is found. Interestingly, the calculated evaporation energies associated with the first solvation shell markedly surpass thermal values, positioning them within the desirable range for hydrogen storage applications. This comprehensive study not only provides insights into the solvation of pristine and protonated cationic Cu clusters but also sheds light on their unique bonding properties.

Experimental and theoretical assessment of the enhanced hydrogen adsorption on polycyclic aromaic hydrocarbons upon decoration with alkali metals. A. M. Reider, S. Kollotzek, P. Scheier, F. Calvo, E. Yurtsever, F. Pirani, M. Bartolomei, M. I. Hernández, T. González-Lezana, J. Campos-Martínez. International Journal of Hydrogen Energy, 48, 525-535 (2024).

DOI: 10.1016/j.ijhydene.2024.01.244

Hydrogen storage by physisorption on carbon-based materials is limited by comparatively low adsorption energies. However, decoration of the carbon substrate with alkali, alkaline earth, or other metal atoms has been proposed as a means to enhance adsorption energies. The decoration affects also the stability of these materials since it makes them more stable and resilient in the repeated cycles of charge and discharge that would be required for a good material devoted to storage. We investigate hydrogen storage capacities of small polycyclic aromatic hydrocarbons (PAHs) cations grown in ultracold helium nanodroplets by analyzing the ion abundances and stabilities. The observations are assessed with quantum chemical calculations and atomistic simulations. It is experimentally shown that the addition of an alkali ion significantly enhances the hydrogen adsorption of the studied PAHs, up to 25% over the bare PAH in the experimental conditions studied here, and the simulations confirm this general trend except for some minor residual discrepancies in the special stabilities (magic numbers). Several approaches to study larger and different PAH compounds are also proposed, and for all cases it is found that alkali decoration increases energy stability by more than 100%.



COSY 1st. General Meeting, Cádiz 1-3, March, 2023


“An Experimental and Theoretical Approach to Hydrogen Attachment
to Alkali Ions Produced in Helium Nanodroplets”

José Campos-Martínez

Helium nanodroplets is a powerful tool to study the production of different charged cluster species as well as their relative stabilities. We present a rather novel method to reversibly attach and detach hydrogen molecules to positively charged sodium clusters formed inside a helium nanodroplet host matrix. In this presentation we will focus on Na +m (H 2 ) n clusters, (m=1,2) and discuss the different properties as well as relative stabilities. The possible use of these alkali ions as dopants to efficently attach hydrogen to carbon substrates will be introduced.

links of interest