Adsorption of Helium and Hydrogen on Triphenylene and 1,3,5-Triphenylbenzene

Stefan Bergmeister (1) , Siegfried Kollotzek (1) , Florent Calvo (2) , Elisabeth Gruber (1) , Fabio Zappa (1) , Paul Scheier (1) , Olof Echt (1, 3)

1 Universität Innsbruck [Innsbruck]
2 LIPhy - Laboratoire Interdisciplinaire de Physique [Saint Martin d’Hères]
3 UNH - University of New Hampshire

The adsorption of helium or hydrogen on cationic triphenylene (TPL, C18H12), a planar polycyclic aromatic hydrocarbon (PAH) molecule, and of helium on cationic 1,3,5-triphenylbenzene (TPB, C24H18), a propeller-shaped PAH, is studied by a combination of high-resolution mass spectrometry and classical and quantum computational methods. Mass spectra indicate that HenTPL+ complexes are particularly stable if n = 2 or 6, in good agreement with the quantum calculations that show that for these sizes, the helium atoms are strongly localized on either side of the central carbon ring for n = 2 and on either side of the three outer rings for n = 6. Theory suggests that He14TPL+ is also particularly stable, with the helium atoms strongly localized on either side of the central and outer rings plus the vacancies between the outer rings. For HenTPB+, the mass spectra hint at enhanced stability for n = 2, 4 and, possibly, 11. Here, the agreement with theory is less satisfactory, probably because TPB+ is a highly fluxional molecule. In the global energy minimum, the phenyl groups are rotated in the same direction, but when the zero-point harmonic correction is included, a structure with one phenyl group being rotated opposite to the other two becomes lower in energy. The energy barrier between the two isomers is very small, and TPB+ could be in a mixture of symmetric and antisymmetric states, or possibly even vibrationally delocalized

Mots clés: noble gases; helium; hydrogen; PAH; triphenylene; 1 3 5-triphenylbenzene; adsorption; mass spectrometry; path-integral molecular dynamics simulations

Domaines: Chimie théorique et/ou physique

Stefan Bergmeister, Siegfried Kollotzek, Florent Calvo, Elisabeth Gruber, Fabio Zappa, et al.. Adsorption of Helium and Hydrogen on Triphenylene and 1,3,5-Triphenylbenzene. Molecules, 2022, 27 (15), pp.4937. ⟨10.3390/molecules27154937⟩. ⟨hal-03854328⟩