Bond Dissociation and Reactivity of HF and H₂O in a Nano Test Tube

Molecular
motion and bond dissociation are two of the most fundamental
phenomena underpinning the properties of molecular materials. We entrapped
HF and H2O molecules within the fullerene C60 cage, encapsulated within a single-walled carbon nanotube (X@C60)@SWNT, where X = HF or H2O. (X@C60)@SWNT represents a class of molecular nanomaterial composed of a
guest within a molecular host within a nanoscale host, enabling investigations
of the interactions of isolated single di- or triatomic molecules
with the electron beam. The use of the electron beam simultaneously
as a stimulus of chemical reactions in molecules and as a sub-angstrom
resolution imaging probe allows investigations of the molecular dynamics
and reactivity in real time and at the atomic scale, which are probed
directly by chromatic and spherical aberration-corrected high-resolution
transmission electron microscopy imaging, or indirectly by vibrational
electron energy loss spectroscopy in situ during
scanning transmission electron microscopy experiments. Experimental
measurements indicate that the electron beam triggers homolytic dissociation
of the H–F or H–O bonds, respectively, causing the expulsion
of the hydrogen atoms from the fullerene cage, leaving fluorine or
oxygen behind. Because of a difference in the mechanisms of penetration
through the carbon lattice available for F or O atoms, atomic fluorine
inside the fullerene cage appears to be more stable than the atomic
oxygen under the same conditions. The use of (X@C60)@SWNT,
where each molecule X is “packaged” separately from
each other, in combination with the electron microscopy methods and
density functional theory modeling in this work, enable bond dynamics
and reactivity of individual atoms to be probed directly at the single-molecule
level.