Adsorption of helium on a charged propeller molecule: hexaphenylbenzene

Abstract

Physisorption on planar or curved graphitic surfaces or aromatic rings has been investigated by various research groups, but in these studies, the substrate was usually strictly rigid. Here, we report a combined experimental and theoretical study of helium adsorption on cationic hexaphenylbenzene (HPB), a propeller-shaped molecule. The orientation of its propeller blades is known to be sensitive to the environment, with substantial differences between the molecule in the gas phase and in the crystalline solid. Mass spectra of He$$_{n}$$ n HPB$$^{+}$$ + , synthesized in helium nanodroplets, indicate enhanced stability for ions containing $$n = 2, 4, 14, 28, 42, 44$$ n = 2 , 4 , 14 , 28 , 42 , 44 , or 46 helium atoms. Path-integral molecular dynamics simulations reveal a significant dependence of the dissociation energy on the details of the HPB geometry. Good agreement between the experimental data and calculated dissociation energies is obtained, provided that the symmetry of HPB$$^{+}$$ + is reduced from $$D_{6}$$ D 6 to $$D_{2}$$ D 2 , such a lower symmetry being suggested from quantum chemical calculations as arising upon electron removal. Graphic Abstract

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

“…In our previous work, we investigated helium adsorption on another cationic propeller-shaped molecule, namely hexaphenylbenzene (C 42 H 30, HPB) [ 28 ]. The orientation of its phenyl groups is known to strongly depend on the environment but, generally, those structures have a 6-fold rotational symmetry for the neutral molecule.…”

“…He n TPL + , (H 2 ) n TPL + , and He n TPB + clusters were modeled using a combination of classical global optimization techniques and path-integral molecular dynamics simulations, following earlier works [ 2 , 28 , 33 ]. Briefly, we used a many-body force field to describe the interaction between the adsorbed atoms or molecules and the hydrocarbon ion, consisting of additive repulsion–dispersion interaction between the ligands and the C- or H-atoms of the solvated ion, and a polarizable contribution felt by each ligand resulting from the distribution of partial charges on the hydrocarbon cation.…”

“…Quantum effects may also hinder the formation of a commensurate adsorption layer. Helium atoms and hydrogen molecules adsorbed on fullerenes [ 1 , 2 , 3 , 4 , 12 ] or polycyclic aromatic hydrocarbons (PAHs) [ 18 , 19 , 20 , 21 , 22 , 23 , 24 , 25 , 26 , 27 , 28 , 29 ] may exhibit strong vibrational delocalization, depending on the density of the adsorbed layer and the charge of the substrate.…”

“…To assist with the interpretation of these measurements, we also carried out an atomistic modeling of He n TPL + , (H 2 ) n TPL + , and He n TPB + using the same computational methodology as in earlier works [ 2 , 28 , 29 , 33 ]. In TPB + the phenyl groups are rotated out of the plane and two nearly isoenergetic isomers exist, one with all blades tilted in the same direction, and another with one blade tilted opposite to the other two.…”

Molecular collisions, photoionization and dynamics: honouring Professor Vincent McKoy

“…Elastic and inelastic scattering of lowenergy electrons from gas-phase C 60 : elastic scattering angular distributions and coexisting solid-state features have been revisited by Tanaka et al [12] while Cl − kinetic-energy release distributions from chlorobenzene and related molecules in electron transfer experiments were presented by Kumar et al [13]. A combined experimental and theoretical study of helium adsorption on cationic hexaphenylbenzene (HPB), a propeller-shaped molecule, was investigated [14], and molecular synthesis in ices triggered by dissociative electron attachment to carbon monoxide was presented by Schmidt et al [15]. García-Abenza and co-workers [16] reported on a complete data set for the simulation of electron transport through gaseous tetrahydrofuran in the energy range 1-100 eV as a significant attempt to understand radiation damage in biological related molecules particle track simulations, whilst Randi et al [17] described elastic, electronically inelastic, total ionization and total cross sections for the scattering of electrons by trans-formic acid.…”