In recent years, one of the more promising and growing fields in the physical sciences has been mode-selective chemistry,’ which focuses on removing undesired byproducts of commercial chemical reactions, thus increasing the yield of the desired commercial product.‘
Most of the techniques used in this field involve high precision lasers. However, scientists at Brookhaven National Laboratories, along with collaborators at the Fritz-Haber-Institut inGermany, have discovered new techniques involving the use of low temperature Scanning Tunneling Microscopy.‘
STM works through manipulating and detecting electrons from both the microscope as well as the sample.’ By allowing these electrons to interact, scientists can potentially determine the structure of the sample on an atomic level.’ More importantly, scientists can use these techniques to cause the sample to move to a site of higher reactivity.‘
‘We found that the motion of the molecule can be controlled by tuning the parameters of the tunneling electrons: the electronic current and energy,’ said Zhen Song, a research associate at Brookhaven National Laboratories.’ ‘We are able to select a particular reaction pathway by adjusting the electronic tunneling current and energy.’‘
If thoroughly developed for commercial use, STM can have a great impact on the chemical industry.’ Reaction pathways that are desired can be favored to a far greater degree than they have been through current mode-selective chemistry techniques.’ Consequently, the amount of waste products accumulated will decrease significantly, and more of the desired product will be attained.’ Furthermore, STM may also provide reaction pathways that are completely unattainable currently.‘
Such pathways are achieved by providing a certain amount of energy to a reaction through electron tunneling.’ When energy above a certain threshold is given to the system, tunneling electrons induce molecular vibrations that cause molecules to move to regions on the substrate where more efficient and productive reactions can occur.’ Below this threshold energy, the molecules simply disassociate from the substrate.’ ‘
Though Song has only tested these methods on simple ammonia and copper substrate systems, she realizes that they can also be applied to more difficult processes.‘
‘It would be interesting to extend this methodology to more complex processes, for example, by searching for strategies of controlling and enhancing reactivity at surfaces through the discovery of new reaction pathways that are inaccessible via classical ‘thermal’ chemistry,’ Song said. STM techniques are further proof of how modern technology has allowed scientists to manipulate and even control the smallest types of matter.’ ‘
‘ ‘As a chemistry major, it really does give me something to think about,’ said Brian Friedlich, a junior atStonyBrookUniversity .’ ‘The mechanisms and pathways that we learn about now would become arbitrary.’ Chemists would simply design their own mechanisms by predetermining exactly what substances interact.’‘
Ultimately, mode-selective chemistry will provide more efficient and cost-effective methods of chemical manufacturing, and bring us to a more enlightened understanding of how molecular interactions occur.
