21 research outputs found
Influence of Dispersion Interactions on the Thermal Desorption of Nonplanar Polycyclic Aromatic Hydrocarbons on HOPG
A combination of low energy ion beam deposition and mass resolved thermal desorption spectroscopy is applied to analyze the binding behavior of two nonplanar polycyclic aromatic hydrocarbons (PAHs) to highly oriented pyrolytic graphite (HOPG) surfaces—also concerning their lateral dispersion interactions. In particular, the fullerene precursor C60H30 (FPC) and rubrene C42H28 are studied. Due to their smaller contact areas, both molecules exhibit significantly weaker binding energies to the HOPG surface compared to planar PAHs of similar size: C60H30 is bound to the surface by 3.04 eV, which is 0.6 eV lower than for a fully planar homologue. For rubrene, an isolated molecule–substrate binding energy of 1.59 eV is found, which is about 1 eV less than that of the corresponding planar homologue hexabenzocoronene C42H18. In contrast to FPC, rubrene shows a significant (intermolecular) lateral dispersion contribution to the binding energy as the submonolayer coverage increases
Influence of Dispersion Interactions on the Thermal Desorption of Nonplanar Polycyclic Aromatic Hydrocarbons on HOPG
A combination of low energy ion beam deposition and mass resolved thermal desorption spectroscopy is applied to analyze the binding behavior of two nonplanar polycyclic aromatic hydrocarbons (PAHs) to highly oriented pyrolytic graphite (HOPG) surfaces—also concerning their lateral dispersion interactions. In particular, the fullerene precursor C60H30 (FPC) and rubrene C42H28 are studied. Due to their smaller contact areas, both molecules exhibit significantly weaker binding energies to the HOPG surface compared to planar PAHs of similar size: C60H30 is bound to the surface by 3.04 eV, which is 0.6 eV lower than for a fully planar homologue. For rubrene, an isolated molecule–substrate binding energy of 1.59 eV is found, which is about 1 eV less than that of the corresponding planar homologue hexabenzocoronene C42H18. In contrast to FPC, rubrene shows a significant (intermolecular) lateral dispersion contribution to the binding energy as the submonolayer coverage increases
From Planar to Cage in 15 Easy Steps: Resolving the C<sub>60</sub>H<sub>21</sub>F<sub>9</sub><sup>–</sup> → C<sub>60</sub><sup>–</sup> Transformation by Ion Mobility Mass Spectrometry
A combination
of mass spectrometry, collision-induced dissociation,
ion mobility mass spectrometry (IM-MS), and density functional theory
(DFT) has been used to study the evolution of anionic species generated
by laser-desorption of the near-planar, fluorinated polycyclic aromatic
hydrocarbon (PAH), C<sub>60</sub>H<sub>21</sub>F<sub>9</sub> (s).
The dominant decay process for isolated, thermally activated C<sub>60</sub>H<sub>21</sub>F<sub>9</sub><sup>–</sup> species comprises
a sequence of multiple regioselective cyclodehydrofluorination and
cyclodehydrogenation reactions (eliminating HF and H<sub>2</sub>,
respectively, while forming additional pentagons and/or hexagons).
The DFT calculations allow us to set narrow bounds on the structures
of the resulting fragment ions by fitting structural models to experimentally
determined collision cross sections. These show that the transformation
of the precursor anion proceeds via a series of intermediate structures
characterized by increasing curvature, ultimately leading to the closed-shell
fullerene cage C<sub>60</sub><sup>–</sup> as preprogrammed
by the precursor structure