An international group has observed at BESSY II how heavy molecules, specifically bromochloromethane, break apart into smaller pieces when they absorb X-ray light. By utilizing a newly developed analytical technique, they successfully visualized the ultra-quick dynamics of this phenomenon. When X-ray photons hit the molecules, a “molecular catapult effect” is triggered: lighter atomic groups are expelled first, resembling projectiles launched from a catapult, while the heavier atoms—bromine and chlorine—detach at a slower pace.
An international group has observed at BESSY II how heavy molecules—specifically bromochloromethane—break apart into smaller pieces when they absorb X-ray light. By utilizing a newly developed analytical technique, they successfully visualized the ultra-quick dynamics of this phenomenon. When X-ray photons hit the molecules, a “molecular catapult effect” is triggered: lighter atomic groups are expelled first, resembling projectiles launched from a catapult, while the heavier atoms—bromine and chlorine—detach at a slower pace.
When X-rays interact with molecules, they can dislodge electrons from certain orbitals, driving them into high-energy states, which results in the breaking of chemical bonds. This process often occurs incredibly quickly, within just a few femtoseconds (10-15 s). While this has been explored in lighter molecules like ammonia, oxygen, hydrochloric acid, or simple carbon compounds, there has been limited research on molecules that contain heavier atoms.
Now, a collaborative team from France and Germany has investigated the rapid breakdown of halogen-containing molecules. Their focus was on a molecule that has bromine and chlorine atoms connected by a lighter bridge, known as an alkylene group (CH2). The experiments took place at the XUV beamline of BESSY II.
The absorption of X-rays led to the breaking of molecular bonds, resulting in ionic fragments that were then analyzed. The scientists managed to create a visualization from the collected measurement data, illustrating how atoms move in the transient states right before the bonds rupture. To achieve this, the team developed a new analytical approach named IPA (Ion Pair Average) and combined it with theoretical calculations to reconstruct the dynamics of the process.
The findings demonstrate that lighter atomic groups, such as CH2, are expelled first, while the heavier bromine and chlorine atoms remain and, as a result, separate at a slower rate. Notably, this catapult-like behavior occurs only at specific X-ray energy levels. Theoretical models, corroborating the experimental results, highlight the importance of vibrations of the lighter atomic groups in triggering these rapid reactions.
“This study showcases the distinct dynamics of molecular disintegration when exposed to X-ray radiation,” states Dr. Oksana Travnikova (CNRS, Université Sorbonne, France), the lead author of this recently published study in J. Phys. Chem. Lett. It particularly illustrates how the catapult-like motion of lighter groups sets off the separation of heavier fragments in an impressively short timeframe. These discoveries may enhance our comprehension of chemical reactions at the molecular scale and provide insights into how high-energy radiation impacts complex molecules.
