Scientists get closer look at molecular interaction

Researchers at the University if Rochester have devised a method to determine the alignment of a molecule’s axis, the ‘poles’ that govern how a molecule will interact with others.

The research is said to show how a tightly focused laser employing a new kind of polarisation can produce valuable images of individual molecules in three dimensions.

The new method takes a snapshot of a phenomenon called the ‘molecular dipole moment.’ This ‘moment’ is an axis that runs through the molecule like a north and south pole, along which energy is emitted and absorbed.

If two molecules are positioned so that their respective poles align, they are more likely to exchange energy. If they are completely misaligned, then an interaction is more difficult. Someday, researchers hope to control the alignment to direct chemical reactions at the atomic level.

‘By imaging the dipole movement of certain molecules we can see exactly how certain chemical reactions happen,’ said Lukas Novotny, assistant professor of optics at the University of Rochester.

Determining the north pole of an atom required a new class of light polarisation, the development of which was pioneered by Thomas Brown, associate professor of optics at the University.

Regular light has linear polarisation, which means it essentially vibrates within a plane. The molecule-imaging method, however, uses radial polarisation, where the vibration moves in several planes radiating outward from the light beam.

By converting regular laser light to radial-polarised light and tightly focusing the laser beam, the team can create a tiny electric field that is of equal strength in all three dimensions, due to the radial polarisation.

The team then scans the beam along the molecule in all directions until one of the radial planes lines up with the north or south pole, and the atom absorbs the energy. A slight burst of fluorescence tells the team when they’ve hit their mark, and they can determine at exactly what angle the pole is oriented.

Tracking the dipole moments might shed light on how cancer cells grow in colonies. Novotny predicts that someday molecular dipole moments may be not just ascertained but controlled, allowing for quick, custom-made molecule alignment, or even data storage, since the orientation of the dipole moment could stand for a one or zero.