Molecules ‘quantum rattle’ in buckyball cage

U. NOTTINGHAM / U. SOUTHAMPTON (UK) — The space inside carbon “buckyballs” can imprison other smaller molecules like hydrogen or water and reveal their “quantum rattle.”

The nano-meter sized cavity of the hollow spherical C60 Buckminsterfullerene—or buckyball—effectively creates a “nanolaboratory,” allowing detailed study of the quantum mechanical principles that determine the motion of the caged molecule, including the mysterious wave-like behavior that is a fundamental property of all matter.

Experiments by the international team of researchers, including physicists from the University of Nottingham, have revealed the wave-like behavior and show how the imprisoned H2 and H2O molecules ‘quantum rattle’ in their cage.


Professor Tony Horsewill of the School of Physics and Astronomy says: “For me a lot of the motivation for carrying out this investigation came from the sheer pleasure of studying such a unique and beautiful molecule and teasing out the fascinating insights it gave into the fundamentals of quantum molecular dynamics. Intellectually, it’s been hugely enjoyable.

“However, as with any blue-skies research initiative there is always the promise of new, often unforeseen, applications. Indeed, in the case of water molecules inside buckyballs we have a guest molecule that possesses an electric dipole moment and the collaboration is already investigating its use in molecular electronics, including as an innovative component of a molecular transistor.”

The research has recently been published in Proceedings of the National Academy of Sciences.

The discovery of the C60 Buckminsterfullerene, and the related class of molecules the fullerenes, in the mid-1980s earned Professors Harry Kroto, Robert Curl, and the late Richard Smalley the Nobel Prize in Chemistry in 1996.

It has a cage-like spherical structure made up from 20 hexagons and 12 pentagons and resembles a soccer ball, earning it the nickname “buckyball.”

Molecular surgery

In a recent breakthrough in synthetic chemistry, Japanese scientists from Kyoto have invented a molecular surgery technique allowing them to successfully permanently seal small molecules such as H2 and H2O inside C60.

They used a set of surgical synthetic procedures on the C60 “cage” that produced an opening large enough to “push” an H2 or H2O molecule inside at high temperature and pressure. The system was then cooled down to stabilize the entrapped molecule inside and the cage was surgically repaired to reproduce a C60.

Horsewill adds: “This technique succeeds in combining perhaps the universe’s most beautiful molecule C60 with its simplest.”

The Nottingham research group has employed a technique called inelastic neutron scattering (INS) where a beam of neutrons—fundamental particles that make up the atomic nucleus—is used to investigate the “cage rattling” motion of the guest molecules within the C60.

Their investigations have given an insight into the wavelike nature of H20 and H2 molecules and their orbital and rotational motion as they move within the C60.

New types of water

Professor Malcolm Levitt, of the School of Chemistry at the University of Southampton, who has used the technique nuclear magnetic resonance (NMR) to study the quantum properties of the caged molecules, says: “By confining small molecules such as water in fullerene cages we provide the controlled environment of a laboratory but on the scale of about one nanometer.

“Under these conditions, the confined molecules reveal a wave-like nature and behave according to the laws of quantum mechanics. Apart from their intrinsic interest, we expect that the special properties of these materials will lead to a variety of applications, such as new ways to brighten the images of MRI scans, and new types of computer memory.”

The paper also separately identifies two subtly different forms of H2O—ortho-water and para-water. These so called nuclear spin-isomers also owe their separate identities to quantum mechanical principles.

Researchers from Brown University, as well as scientists in Japan, France, Estonia, and the UK contributed to the findings.

Source: University of Nottingham