Researchers have used ultra-high-speed x-ray pulses to make a high resolution "film" of a molecule that undergoes structural movements. The research, published in Nature Chemistry reveals the dynamics of the process in unforeseen details ̵
The ability to see real-time molecular movements gives insights into chemical dynamics processes that were unthinkable a few decades ago, the researchers say and can ultimately help optimize reactions and design new types of chemistry.
"For many years, chemists have learned chemical reactions by mainly studying the molecules that exist before and after a reaction has occurred," says Brian Stankus, a new doctoral student. degree from Brown University and co-author of the paper. "It was impossible to actually look at chemistry as it happens because most molecular transformations happen very quickly. But ultra-fast light sources such as the one we used in this experiment have enabled us to measure real-time molecular movements and this is the first time these sorts of subtle effects have been perceived with such clarity in an organic molecule of this size. "The work is a collaboration between Brown chemists, researchers at the SLAC National Accelerator Laboratory and theoretical chemists from the University of Edinburgh in the United Kingdom. was led by Peter Weber, professor of chemistry at Brown.
For the study, the researchers looked at the molecular movements that occur when the organic molecule N-methylmorpholine is excited by pulses of ultraviolet light. X-ray pulses from SLAC's Linac Coherent Light Source (LCLS) were used to capture snapshots in various stages of the molecule's dynamic response.
"We basically hit the molecules with UV light, which initiates the answer and then fractions of one. Secondly, we take a" picture "- we actually take a scatter pattern with an X-ray pulse," says Stankus. "We repeat this and Again, with different ranges between UV pulse and X-ray pulse to create a time series. "X-rays are scattered in special patterns depending on the structure of the molecules. These patterns are analyzed and used to reconstruct a form of the molecule as the molecular motions develop. This pattern analysis was led by Haiwang Yong, a graduate student at Brown and the study's co-author.
The experiment revealed an extremely subtle reaction in which only a single electron becomes tense and causes a clear pattern of molecular vibration. in detail.
"This paper is a true landmark because we were able to measure for the first time the structure of a molecule in an excited state and with time resolution, says Weber, the corresponding author of the study.
"Making these types of almost noise-free measurements in both energy and time is not a small achievement," said Mike Minitti, a senior SLAC staff researcher, studying co-authors. "Over the past seven years, our collaboration has learned a lot about how to best use different LCLS diagnostics to accurately measure small oscillations in X-ray intensities and, to an even greater extent, track the fifty-second time scale changing molecules. All this has informed the development of customized data analysis routines that virtually eliminate unsteady, unwanted signals to our data. These results demonstrate the fidelity we can achieve. "A particularly interesting aspect of the reaction, researchers say, is that it is coherent when groups of these molecules interact with light, their atoms vibrate in interaction with each other.
"If we can use experiments like this to study how precise light can be used to control the collective movement of billions of molecules, we can design systems that can be consistently controlled," says Stankus. "Simple: If we understand exactly how light leads molecular movements we can design new systems and direct them to make useful chemistry. "
Look at molecules shared in real time
Brian Stankus et al., Ultrafast X-ray scattering reveals vibrational coherence after Rydberg excitation, Nature Chemistry (2019). DOI: 10,1038 / s41557-019-0291-0
Captured in the Act: Pictures Capture Molecular Movements in Real Time (2019, July 11)
July 12, 2019
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