Findings that would help further understand how living tissue reacts to radiation exposure.
Energy flows through a system of atoms or molecules by a series of processes like transfers, emissions, or decay. You can visualize a number of these details like passing a ball (the energy) to somebody else (another particle), except the pass happens quicker than the blink of an eye, so fast that the details about exchange aren’t well understood. Imagine same exchange happening in busy room, with others bumping into you and usually complicating and slowing the pass. Then, imagine what proportion faster the exchange would be if everyone stepped back and created a secure bubble for the pass to happen unhindered.
An international collaboration of scientists, including UConn Professor of Physics Nora Berrah and post-doctoral researcher and lead author Aaron LaForge, witnessed this bubble-mediated enhancement between two helium atoms using ultrafast lasers. Their results are now published in Physical Review X.
Measuring energy exchange between atoms requires almost inconceivably fast measurements, says LaForge.
“The reason why shorter time scales are needed is that once you check out microscopic systems, like atoms or molecules, their motion is extremely fast, roughly on the order of femtoseconds (10-15 s ), which is that the time it takes them to maneuver a couple of angstroms (10-10 m),” LaForge says.
Laforge explains these measurements are made with a so-called free-electron laser, where electrons are accelerated to just about the speed of light, then using sets of magnets, the electrons are forced to undulate, which causes them to release short wavelength bursts of light. “With ultrafast laser pulses you can time-resolve a process to know how briskly or slow something occurs,” says LaForge.
The first step of the experiment was to initiate the method , says LaForge: “Physicists probe and perturb a system in-order-to measure response by taking fast snapshots of the reaction. Thus, essentially, we aim to form a molecular movie of the dynamics. In this case, we first initiated the formation of 2 bubbles in helium nanodroplet. Then, use a second pulse, we determined how briskly they were ready to interact.”
With a second laser pulse the researchers measured how the bubbles interact: “After exciting the 2 atoms, two bubbles are formed round the atoms. Then the atoms could move and interact with each other without having to push against surrounding atoms or molecules,” says LaForge.
Helium nanodroplets were used as a model system, since helium is one among the only atoms in periodic table , which LaForge explains is a crucial consideration. albeit there are up to roughly 1,000,000 helium atoms within a nanodroplet, the electronic structure is comparatively simple, and therefore the interactions are easier elucidate with fewer elements in system to account for.
“If you go-to more complex systems, things can get more complicated rather quickly. as an example , even liquid water is pretty complicated, since there are often interactions within the molecule itself or it can interact with its neighboring water molecules,” LaForge says.
Along with bubble formation and therefore the subsequent dynamics, the researchers observed energy transfer, or decay, between the excited atoms, which was over an order of magnitude faster than previously expected – as fast as 400 femtoseconds. At first, they were a bit perplexed about the way to explain such a quick process. They approached theoretical physicist colleagues who could perform state-of-the-art simulations to understand better about the problem.
Below may be a real-time theoretical simulation of the merging of two bubble-encapsulated excited helium atoms within a liquid helium.
“The results of our investigation were unclear but collaboration with theorists allowed us to nail down and explain the phenomenon,” says LaForge.
He points out that an exciting aspect of the research is that we can push envelope further in understanding the basics of those ultrafast processes and pave the way for brand new research. the large innovation is having the ability to make a way to measure interactions down femtosecond or maybe attosecond (10-18 s) timescales. “It’s really rewarding once you can perform a rather fundamental experiment which will even be applied to something more complex,” says LaForge.
The process the researchers observed is named Interatomic Coulombic Decay (ICD), and is a important means for atoms or molecules to share and transfer energy. The bubbles enhanced the process, demonstrating how the environment can alter the speed at which a process occurs. Since ICD plays a crucial role in how living tissues react to radiation exposure – by creating low energy electrons which may continue to cause damage within tissues — these findings are of biological importance, because it’s likely that similar bubbles would form in other fluids, like water, and with other molecules like proteins.
“Understanding the timescale of energy transfer at the microscopic scale is important to numerous scientific fields, like physics, chemistry, and biology. The fairly recent development of intense, ultrafast laser technology allows for time-resolved investigations with unprecedented detail, opening up a wealth of latest information and knowledge,” says Berrah.
The findings are reported in Physical Review X.
