Adsorption of hydrogen on neutral and charged fullerene: Experiment and theory

Abstract

A consistent and accurate ab initio parametrization of density functional dispersion correction (DFT-D) for the 94 elements H-Pu The Journal of Chemical Physics 132, 154104 (2010) Helium droplets are doped with fullerenes (either C 60 or C 70 ) and hydrogen (H 2 or D 2 ) and investigated by high-resolution mass spectrometry. In addition to pure helium and hydrogen cluster ions, hydrogen-fullerene complexes are observed upon electron ionization. The composition of the main ion series is (H 2 ) n HC m + where m = 60 or 70. Another series of even-numbered ions, (H 2 ) n C m + , is slightly weaker in stark contrast to pure hydrogen cluster ions for which the even-numbered series (H 2 ) n + is barely detectable. The ion series (H 2 ) n HC m + and (H 2 ) n C m + exhibit abrupt drops in ion abundance at n = 32 for C 60 and 37 for C 70 , indicating formation of an energetically favorable commensurate phase, with each face of the fullerene ion being covered by one adsorbate molecule. However, the first solvation layer is not complete until a total of 49 H 2 are adsorbed on C 60 + ; the corresponding value for C 70 + is 51. Surprisingly, these values do not exhibit a hydrogen-deuterium isotope effect even though the isotope effect for H 2 /D 2 adsorbates on graphite exceeds 6%. We also observe doubly charged fullerene-deuterium clusters; they, too, exhibit abrupt drops in ion abundance at n = 32 and 37 for C 60 and C 70 , respectively. The findings imply that the charge is localized on the fullerene, stabilizing the system against charge separation. Density functional calculations for C 60 -hydrogen complexes with up to five hydrogen atoms provide insight into the experimental findings and the structure of the ions. The binding energy of physisorbed H 2 is 57 meV for H 2 C 60 + and (H 2 ) 2 C 60 + , and slightly above 70 meV for H 2 HC 60 + and (H 2 ) 2 HC 60 + . The lone hydrogen in the odd-numbered complexes is covalently bound atop a carbon atom but a large barrier of 1.69 eV impedes chemisorption of the H 2 molecules. Calculations for neutral and doubly charged complexes are presented as well.

Adsorption of helium on isolated C60and C70anions

“…At the same time, curvature increases the distance between atoms adsorbed at hollow sites to an extent that not only helium but even larger particles (including hydrogen, methane, ethylene or nitrogen) can be accommodated in the 1 × 1 phase of C 60 , with one particle each at the centres of the 12 pentagons and 20 hexagons (25 hexagons for C 70 ) [19,22,24,25], for a review see [12]. The anomaly at n = 32 also appeared in mass spectra of C 60 that was allowed to react in a gas aggregation cell with red phosphorous [26] or alkaline earth metals [27].…”

“…Mass spectra were evaluated by means of a customdesigned software [21,22]. The routine includes automatic fitting of Gaussians to the mass peaks and subtraction of background by fitting a spline to the background level of the raw data.…”

Adsorption of sodium and cesium on aggregates of C60

“…Mass spectra were evaluated by means of customdesigned software [26,27]. The routine includes automatic fitting of Gaussians to the mass peaks and subtraction of background by fitting a spline to the background level of the raw data.…”

Adsorption of molecular hydrogen on coronene with a new potential energy surface

“…Attachment of H 2 and D 2 to fullerenes has been also experimentally investigated in comparison with some other physisorbed species such as rare gases (RG) or N 2 : The electronic absorption spectra recorded by Holt et al 26 revealed a marked influence of the corresponding ligand. The theory versus experiment comparison performed by Kaiser et al 27 on helium droplets doped with fullerenes and hydrogen (H 2 or D 2 ) revealed the effect of the surface curvature to accommodate hosting species inside the PAH.…”