For the very first time, researchers have used laser beams to build new molecules. In a research, recently published in the Physical Review Letters journal, a team of scientists, from the Hebrew University of Jerusalem, the Technion-Israel Institute of Technology and the Germany-based University of Kassel, has successfully altered the chemical bonding between atoms, using the coherent light from lasers.
Central to the study is the concept of coherent control, i.e. the use of light to manipulate chemical reactions, such as the bond-forming process between atoms. Over the years, researchers have used lasers to break the electron bonds in a molecule, as a way of tearing the constituent atoms apart. When it comes to the reverse, however, the scientific world was , until now, in the dark. The new research reveals the exciting possibilities of using laser beams to create entirely new molecules. Speaking about the project, Christiane Koch, a scientist at the University of Kassel, said:
Coherent control, that is the use of matter–wave interferences [in atoms] to steer a dynamical process towards a certain target [using light], has always fascinated me. It seemed very unsatisfactory that even though [it] was conceived to steer chemical reactions, nobody seemed to be able to do it… Laser-induced bond formation in a gas is a low probability event, so it was crucial to find a way to detect it unambiguously.
For the experiment, they bombarded a tiny group of magnesium atoms, with ultrashort laser pulses. This caused the atoms to combine, thus forming small amounts of a molecular complex, called magnesium dimer (Mg2). Furthermore, by changing the pulse shape, the team was able to increase the amount of product generated, by a factor of five. To ensure that the molecules are formed as a result of coherent control, and not due to some random process, the scientists conducted further tests, using femtosecond lasers with pulse duration of a millionth of one billionth of a second. According to the researchers, the low yield is primarily because of the fact that, for two atoms to bond together, the electron orientations of both should be the same at the moment when the laser pulse strikes them. Koch explains:
A very short and intense laser pulse is shone onto a gas of atoms. The energy absorbed from the pulse leads to a rearrangement of the atoms’ electrons, resulting in a chemical bond.
With further development, the researchers believe, the breakthrough could help reduce processing costs of the chemical industry, as well as pave the way for an entirely new arena of photochemistry.