Understanding chemical reactions in space is incredibly difficult. First of all, the extremely cold temperatures would all but preclude most chemicals mixing, as there is simply insufficient energy to ignite the reactions. Yet, observational data suggests that complex compounds are being created in this inhospitable environment. Now, however, a new study reveals that a quantum effect known to be the key in stellar physics may also be the missing piece in space chemistry.
When atoms approach each other, they are repelled by electrostatic force. Simply put, like charges repel, and do so with such force that bonding even individual charges together — such as hydrogen nuclei — would be impossible according to classical physics.
But a quantum principle known as quantum tunneling allows atomic particles to “tunnel” through the electrostatic barrier and allow the nuclear strong force to bind the charges together. This process allows for nuclear fusion to occur and, ultimately, powers our Sun. In stellar cases at least, it is the extremely high temperatures present at the cores of these stars that makes the quantum tunneling possible. Now, researchers at the University at Leedsbelieve that this same principle could also be responsible for creating compounds in the extreme coldness of outer space.
The Leeds team examined specifically the problem of how methoxy radicals are created in space. Previous work had found that such molecules existed in space, but their creation could not be explained by traditional explanations. Instead, “we suggest that an ‘intermediary product’ forms in the first stage of the reaction, which can only survive long enough for quantum tunneling to occur at extremely cold temperatures,” says Professor Dwayne Heard, Head of the School of Chemistry at the University of Leeds, who led the project.
In this new work, methanol and an oxidizing chemical called the ‘hydroxyl radical’ were allowed to mix at minus 210 degrees Celsius, simulating conditions of deep space. They found that the methoxy radicals were produced as a result of quantum tunneling. Not only that, but the reaction rate was 50 times that of similar mixing at room temperature.
Achieving this exciting result was an arduous process, as properly simulating the space environment without corrupting the chemical components proved challenging. “The problem is that the gases condense as soon as they hit a cold surface,” says Robin Shannon from the University of Leeds, who performed the experiments. “So we took inspiration from the boosters used for the Apollo Saturn V rockets to create collimated jets of gas that could react without ever touching a surface.”
Because of the unusually high reaction rate observed in this initial trial, the team is now turning their attention to other alcohol reactions to search for similar reaction rate boosting due to quantum tunneling. “If our results continue to show a similar increase in the reaction rate at very cold temperatures, then scientists have been severely underestimating the rates of formation and destruction of complex molecules, such as alcohols, in space,” concludes Heard.