4.6 Article

Solvation of Large Polycyclic Aromatic Hydrocarbons in Helium: Cationic and Anionic Hexabenzocoronene

Journal

MOLECULES
Volume 27, Issue 19, Pages -

Publisher

MDPI
DOI: 10.3390/molecules27196764

Keywords

helium; PAH; hexabenzocoronene; adsorption; mass spectrometry; path-integral molecular dynamics simulations

Funding

  1. Austrian Science Fund, FWF [I4130, P31149, P34563, T1181, W1259-N27]
  2. Austrian Science Fund (FWF) [I4130, T1181, P34563] Funding Source: Austrian Science Fund (FWF)

Ask authors/readers for more resources

The adsorption behavior of helium on the surface of charged hexabenzocoronene was investigated, showing that the arrangement of helium atoms depends on the charge of the substrate. Quantum calculations revealed that the adsorbate layer grows by filling concentric rings around the central benzene ring. The first three rings exhibit a frozen arrangement, while the subsequent layers become three-dimensional and hexagonal.
The adsorption of helium on charged hexabenzocoronene (Hbc, C42H18), a planar polycyclic aromatic hydrocarbon (PAH) molecule of D-6h symmetry, was investigated by a combination of high-resolution mass spectrometry and classical and quantum computational methods. The ion abundance of He(n)Hbc(+) complexes versus size n features prominent local anomalies at n = 14, 38, 68, 82, and a weak one at 26, indicating that for these magic sizes, the helium evaporation energies are relatively large. Surprisingly, the mass spectra of anionic He(n)Hbc(-) complexes feature a different set of anomalies, namely at n = 14, 26, 60, and 62, suggesting that the preferred arrangement of the adsorbate atoms depends on the charge of the substrate. The results of our quantum calculations show that the adsorbate layer grows by successive filling of concentric rings that surround the central benzene ring, which is occupied by one helium atom each on either side of the substrate. The helium atoms are fairly localized in filled rings and they approximately preserve the D-6h symmetry of the substrate, but helium atoms in partially filled rings are rather delocalized. The first three rings contain six atoms each; they account for magic numbers at n = 14, 26, and 38. The size of the first ring shrinks as atoms are filled into the second ring, and the position of atoms in the second ring changes from hollow sites to bridge sites as atoms are filled into the third ring. Beyond n = 38, however, the arrangement of helium atoms in the first three rings remains essentially frozen. Presumably, another ring is filled at n = 68 for cations and n = 62 for anions. The calculated structures and energies do not account for the difference between charge states, although they agree with the measurements for the cations and show that the first solvation shell of Hbc(+/-) is complete at n = 68. Beyond that size, the adsorbate layer becomes three-dimensional, and the circular arrangement of helium changes to hexagonal.

Authors

I am an author on this paper
Click your name to claim this paper and add it to your profile.

Reviews

Primary Rating

4.6
Not enough ratings

Secondary Ratings

Novelty
-
Significance
-
Scientific rigor
-
Rate this paper

Recommended

No Data Available
No Data Available