Spanish and Italian scientists have laid down the foundations of a new scientific discipline that pursues to control the movement of electrons in molecules using attosecond methodologies and may open the door to a new way of doing chemistry.
Source: UAM Gazette (July 6, 2017)
An article published in the journal Chemical Reviews, led by Fernando Martín (Universidad Autónoma de Madrid, IMDEA Nanoscience, IFIMAC Condensed Matter Center) and by Mauro Nisoli (Polytenico de Milano) details the bases and the most important milestones of a new scientific discipline: attochemistry.
In general, this discipline seeks to control and manipulate the movement of electrons that form chemical bonds in molecules, using attosecond light pulses (1 attosecond is equivalent to 10-18 seconds). According to the authors, since the structure and reactivity of matter arises from the properties of chemical bonds, attochemistry may enable new reactions and have a direct impact on the development of new substances and materials, making possible a better understanding of the electronic processes that occur in chemical and biological systems.
The study documents the first real-time observation of charge migration processes on molecules of biological interest (as the amino acid phenylalanine, see figure 1), with unprecedented temporal resolution. It also shows the first signs of control of charge migration processes. These observations were made by first irradiating the molecules with a pulse (or pulses) of attosecond light, followed by a second pulse of equal or greater duration, which captures an image of the electronic motion at a particular instant. The variation of the elapsed time between the first and second pulses provides a sequence of images of the electronic motion, which allows the selection of the precise instant in which the localization of the charge may favour (or prevent) a certain chemical reaction .
From femtochemistry to attochemistry
Chemical reactions are the result of bond-formation and bond-breakage and, during this process, atoms in molecules may arrange to form a new substance. Reactivity, the essence of chemistry, is a dynamic process that results from the movement of electrons and atomic nuclei. These movements occur in an ultrafast time scale, ranging from femtoseconds (10-15 seconds), typical of nuclear movement, to attoseconds, typical of electronic movement.
In this sense, all the chemistry could be understood as femtochemistry or attochemistry. Femtochemistry, born in the second half of the last century, is now a well-established scientific discipline whose main objective is to control a chemical reaction by directing the movement of the nuclei of the involved molecules using femtosecond pulses of light. Today, femtosecond lasers are widely used in most areas of the chemical sciences and in many laboratories.
The 21st century has brought remarkable advances in the manufacture of coherent light sources that allow the generation of even shorter pulses of light, with durations that reach the few tens of attoseconds, in the extreme ultraviolet frequency region.
These advances have led to a substantial evolution of laser technology in recent years, enabling for the first time a direct control of the ultra-rapid movement of electrons within a molecule and, consequently, the nuclear dynamics induced by such electronic movement, which occurs at longer time scales.
Since the distribution of electrons in the molecule, or electronic density, is ultimately responsible for the formation and breaking of bonds, the control of this movement has opened the door to a new way of doing chemistry.
This research has received funds from the European Research Council, under the ERC Advanced Grant nº 290853, and the principal investigator of this project, Fernando Martín, has been awarded with the prize King Jaime I 2017, in the category of Basic Research.
Reference: Attosecond electron dynamics in molecules. M. Nisoli, P. Decleva, F. Calegari, A. Palacios and F. Martín, Chem. Rev., 2017, 117 (16), pp 10760–10825, DOI: 10.1021/acs.chemrev.6b00453