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

Abstract

Molecular motion and bond dissociation are two of the most fundamental phenomena underpinning properties of molecular materials. We have 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 tri-atomic molecules with the electron beam. The use of the electron beam simultaneously as a stimulus of chemical reactions in molecules and as a sub-Å 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 (Cc/Cs-corrected HRTEM) imaging, or indirectly by vibrational electron energy loss spectroscopy (EELS) in situ during scanning transmission electron microscopy (STEM) 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. Due to a difference in the mechanisms of penetration 2 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 (DFT) modelling in this work, enable bond dynamics and reactivity of individual atoms to be probed directly at the singlemolecule level.

A Singular Molecule-to-Molecule Transformation on Video: The Bottom-Up Synthesis of Fullerene C60 from Truxene Derivative C60H30

“…Continuous video imaging allows for the structural analysis and monitoring of formed intermediates in real-time. Unlike in the case of frequently studied fullerenes ,− ,− or PAHs − ,− entrapped in carbon nanotubes, our molecule is found as an isolated entity on a graphene monolayer. This circumstance prevents the oligomerization process with other fullerenes or molecules and allows us to focus solely on the intramolecular processes in granular detail.…”

“…At this point, it should be mentioned that , unlike in the depiction in Figure a, the vast majority of electrons is scattered at an angle below 5°, as indicated in Figure b by the differential elastic-scattering cross-section for hydrogen at 80 keV kinetic energy. Recently, Biskupek et al demonstrated that the absorbed energy E T of an atom 1 can be further passed to a second atom 2 to give , which follows the relationship expressed in eq 2 in Figure a . The relationship between the e-beam energy uptake of carbon and hydrogen atoms and the transfer to a second atom as a function of acceleration voltage is shown in Figure b.…”

“…Recently, Biskupek et al demonstrated that the absorbed energy E T of an atom 1 can be further passed to a second atom 2 to give E T ′ , which follows the relationship expressed in eq 2 in Figure 5a. 20 The relationship between the e-beam energy uptake of carbon and hydrogen atoms and the transfer to a second atom as a function of acceleration voltage is shown in Figure 5b. Hereby, it becomes evident that, at the utilized acceleration voltage of 80 kV, a homolytic C−H bond cleavage (E d ≈ 7.6 eV, compare Table S4) can occur only upon direct electron−hydrogen atom interaction, whereas secondary energy transfer processes from carbon to hydrogen atoms reach only a value of E max ′ ≈ 4.5 eV, which leads to mere vibrational excitation.…”

“…Hereby, substantial progress in the field of transmission electron microscopy (TEM) was made within the past decade. In the literature often described as single-molecule atomic-resolution real-time electron microscopy (“SMART-EM”) or “chemTEM”, , the direct imaging technique revealed to be especially powerful in the initiation and capture of nonrepetitive events. , For example, the formation of buckyballs from bilayered graphene, which reflects the top-down fullerene formation during the arc-discharge synthesis, was demonstrated in 2010 by Chuvilin et al Further recent highlights comprise the bimolecular reaction of fullerenes, , the reactivity of endohedral fullerenes and their entrapped molecules, the transformations of polycyclic aromatic hydrocarbons to oligomers, − the analysis of reactive metal clusters, − the bonding character of dimeric metal atoms, and even the emerging nucleation of a NaCl nanocrystal . Yet, a discrete multistep synthesis (molecule-to-molecule transformation), which leads to the predicted product and does not terminate in the formation of polymers, was never captured …”

Controlling radiolysis chemistry on the nanoscale in liquid cell scanning transmission electron microscopy

“…16 The G-values are dependent on the energy of the initial fast electron and the chemistry of the liquid sample and often quoted as the number of molecular yield per 100 eV absorbed energy. [20][21] For instance, the G-values of water radiolysis for 300 keV electron beam obtained by Hill and Smith are: 22 that the direct knock-on collisions caused by the electron beam are the main driving force for dissociating water molecules in a specific case of molecular confinement in a sub-nanometre space. They also addressed that the dissociation processes caused by electron-electron interactions such as radiolysis are quickly reversed due to the confined space.…”