Physicists led by Roland Wester of the University of Innsbruck have observed competition between two important reaction mechanisms in organic chemistry in the laboratory. The detailed investigation of the reaction dynamics of a nine-atom reaction compound is unique to date. By doing so, scientists are advancing on a scale that allows applications in many areas of chemistry.
Through laboratory experiments, two-time ERC laureate Roland Wester from the Institute of Ionic and Applied Physics at the University of Innsbruck is trying to take a new look at chemical reactions and better understand their dynamics. Small-molecule interactions are well understood today. Once more than four atoms are included, it becomes difficult for both theory and experiment to describe the course of the reaction in detail. Roland Wester and his team have built a unique experiment in which molecules can interact with ions and monitor them. For the first time, scientists have succeeded in accurately describing the atomic dynamics of the so-called nuclear substitution reaction. A few years ago, a research group investigated the competition between two chemical reactions in organic compounds. In a vacuum chamber, the researchers brought these particles to collide with charged particles from the chemical group of halogens, such as fluorine, iodine and chlorine. For the first time, direct observation has shown that with larger molecules, the removal reaction gains the upper hand and the substitution reaction disappears at some point.
High dimensional interaction dynamics
Until now it was not known what would happen in the size range where both interactions are equally important. To investigate this, further theoretical work was necessary, which has been carried out in recent years by researchers led by Gábor Czakó at Szeged University, Hungary. They calculated the so-called Born-Oppenheimer surface potential, with which the course of the chemical reaction of an eight-atom molecule with a halogen ion can be described in detail. It is noteworthy that the examined reaction occurs in 21 dimensions. The theoretically defined potential landscape provides information about how individual atoms move in this high-dimensional space during a chemical reaction. With this in mind, the Innsbruck scientists working with Eduardo Carrascosa, Jennifer Meyer and Roland Wester were able to create a very accurate prediction of the spatial direction in which the reaction products would fly away in their experiment. It measures the angle and speed at which the ions hit the detector. “And our data shows that we measured exactly what the theory calculated without knowing the empirical data,” Wester says happily. “With so many atoms and therefore so high in dimensions, that has not yet been achieved.”
Thus scientists comprehensively described the chemical reaction, in which two different mechanisms of the reaction occur, theoretically and experimentally. With this work, now published in the journal Nature Chemistry, the Innsbruck scientists are coming into territory regarding the number of atoms involved for the detailed investigation of reaction dynamics, which enables applications in many areas of complex chemical reactions.
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