Volume 93 Issue 26 | pp. 22-23 | Concentrates
Issue Date: June 29, 2015

Femtosecond X-ray Scattering

Chemical Physics: Intense ultrashort X-ray pulses trace ring-opening reaction step-by-step
Department: Science & Technology
News Channels: Analytical SCENE
Keywords: femtosecond, SLAC, ultrafast, X-ray scattering, diffraction
[+]Enlarge
Details of the reaction pathway taken by 1,3-cyclohexadiene during ring opening (lower left to upper right) have been elucidated by probing the process with femtosecond X-ray pulses.
Credit: SLAC National Accelerator Laboratory
Details of the reaction pathway taken by 1,3-cyclohexadiene during ring opening (lower left to upper right) have been elucidated by probing the process with femtosecond X-ray pulses. (The curved surface is a calculated reaction energy diagram used for interpreting experimental data.)
 
Details of the reaction pathway taken by 1,3-cyclohexadiene during ring opening (lower left to upper right) have been elucidated by probing the process with femtosecond X-ray pulses.
Credit: SLAC National Accelerator Laboratory

Researchers in California have used an X-ray scattering method to monitor step-by-step femtosecond structural rearrangements of a molecule undergoing a ring-opening reaction (Phys. Rev. Lett. 2015, DOI: 10.1103/physrevlett.114.255501). The study describes a new ultrafast pump-probe method that deepens understanding of chemical reaction dynamics and lays the groundwork for recording X-ray movies of chemical reactions in real time. To trigger the reaction, Michael P. Minitti of SLAC National Accelerator Laboratory and colleagues irradiated 1,3-cyclohexadiene vapor with ultraviolet laser light, which initiates ring opening and forms several conformers of 1,3,5-hexatriene. Then the team probed the evolution of the diene to the triene by scattering intense 30-femtosecond X-ray pulses from the unfolding molecules. By varying the delay between the UV and X-ray pulses, the team recorded a series of femtosecond X-ray diffraction snapshots, which they analyzed with quantum mechanical methods. The analysis shows that the reaction rapidly expands cyclohexadiene’s carbon bonds and that within one or two oscillations of the carbon skeleton, the C1–C6 bond breaks. The analysis also shows that the reaction’s stereochemical fate is sealed as early as 30 femtoseconds after the UV pulse.

 
Chemical & Engineering News
ISSN 0009-2347
Copyright © American Chemical Society

Leave A Comment

*Required to comment