Nature First evidence of quantum tunneling effects in chemical reactions
On March 1, Professor Roland Wester and his team at the Department of Ion Physics and Applied Physics at the University of Innsbruck published an article in Nature stating that they have measured the quantum tunneling reaction rates of hydrogen molecules with deuterium anions in a low-temperature ion trap and that the measured values agree with the theoretical values, providing the first experimental confirmation of the accuracy of the theoretical model of quantum tunneling effects in chemical reactions.
Tracing quantum mechanical tunneling effects using ion traps
Quantum tunneling effects play an important role in chemistry, whether in gas-phase reactions, surface diffusion or liquid-phase chemistry. Given the high dimensional nature of quantum dynamics, such tunneling reactions are difficult to calculate theoretically and difficult to identify experimentally. Chemists often ignore quantum effects and use classical models to describe reaction processes, but such classical descriptions, which only provide approximations, inevitably have limitations.
While tunneling effects enable reactions to occur, they are inefficient and slow, making experimental observation exceptionally difficult. professor Roland Wester has long wanted to explore this frontier. "I came up with the idea 15 years ago while talking with a colleague at a conference in the United States," Wester recalls. He wanted to trace the quantum mechanical tunneling effect in a very simple reaction.
Quantum mechanics allows particles to react by breaking the energy barrier due to their quantum mechanical fluctuation properties
After several attempts, Roland Wester's team finally chose hydrogen - the simplest element in the universe - as the subject of their experiment. They introduced deuterium (an isotope of hydrogen) into the ion trap, cooled it, and then filled the ion trap with hydrogen. Due to the very low temperature, the negatively charged deuterium ion could not react with hydrogen molecules under classical conditions. However, with the quantum tunneling effect, the two can collide and react with very low probability.
"Quantum mechanics allows particles to break through the energy barrier and react due to their quantum mechanical wave properties," explained Robert Wild, the study's first author. "In the experiment, we gave a possible reaction time of about 15 minutes in the ion trap, and then measured the amount of hydrogen ions formed. From their amount, we can infer how often the reaction occurs."
After fifteen years and the first confirmation of
As shown above, in a low-temperature ion trap containing deuterium anions (D-), the researchers gradually filled it with hydrogen (H2) and the reaction took place under the quantum tunneling effect Picture. Subsequently, the researchers measure the quantities. The number of H- increases linearly at low hydrogen densities, and the researchers believe that the linear deviation of the measured values at high hydrogen densities is related to the heating kinetics of the ion trap. After fitting the data, a very low reaction rate of (5.2 ± 1.6) pictures was finally measured.
In 2018, theoretical physicists calculated that quantum tunneling occurs only once in every 100 billion collisions in this system, which closely matches the experimental results of Wester's team. After 15 years of research, the accuracy of the theoretical model of quantum tunneling effects in chemical reactions was confirmed for the first time.
Better understanding of chemical reactions
The experiments of Wester's team have laid the foundation for a better understanding of many chemical reactions. On the basis of this research, simpler theoretical models of chemical reactions can be developed and tested on reactions that have now been successfully demonstrated. The quantum tunneling effect has also been applied in, for example, scanning tunneling microscopes and atomic clocks, and has also been used to explain the alpha decay of atomic nuclei. Through the tunneling effect, some chemical synthesis of molecules in interstellar clouds can also be explained.
The research was funded by the Austrian Science Foundation FWF and the European Union, among others.
