Scientists have now captured video of the
intimate dance of two atoms as they bond with one another, break apart and come
back together again.
In a sequence of images from an electron
microscope, two atoms of the metal rhenium, bound together to create a molecule,
shimmied around one another, moving closer and then farther apart. In videos of
such molecules, this atomic do-si-do revealed the bond order, or the number of chemical bonds between the two
atoms, and how that bond order changed over time. The closer the atoms were to
one another, the greater the number of bonds. At their closest approach, the
atoms had four bonds tethering them together.
To make imaging easier, scientists trapped
the molecules inside carbon nanotubes. But then, in a fortuitous accident, one molecule
escaped its confinement and nestled into a gap between two nanotubes. There, the
bond between the atoms completely broke before soon reforming, the team reports
January 17 in Science Advances.
Researchers had previously coaxed two atoms to bond (SN: 4/12/18).
But directly observing how chemical bonds change in number “was not done
before,” says physicist Ute Kaiser of Ulm University in Germany.
Kaiser and colleagues made the images
with a transmission electron microscope specially designed to operate at low
voltages, so that its beam of electrons wouldn’t damage the carbon nanotubes or
send the rhenium atoms flying. That electron beam was useful for imaging, but
also served another purpose: It gently jostled the atoms, causing them to dance
rather than sitting still.