Femtosecond Lasers Control Chemical Reactions

Hitting molecules with ultrafast lasers can affect electrons and trigger unaccustomed chemical reactions.

Researchers at the Photonics Institute of the Vienna University of Technology succeeded in directly inducing the splitting of hydrocarbons such as ethylene (C₂H₄) or acetlyene (C₂H₂) into smaller fragments using pairs of femtosecond pulses.

Researchers used a 50 fs pulse to first put the molecules in alignment, then a second, 5 fs pulse to change the state of electrons within the molecules or even ionize them.

Artist's rendering of an ultrafast laser pulse interacting with an ethylene molecule. Courtesy of the Vienna University of Technology.

This interaction is so short it does not have any discernable influence on the more massive atomic nuclei. However, the disturbance of the electron distribution can still initiate chemical processes and eventually separate the nuclei from each other. For instance, the researchers broke up C₂H₂ into CH₂⁺, CH⁺ or carbon ions (C⁺).

“Various reaction paths are possible,” said Dr. Markus Kitzler, senior scientist at the Photonics Institute. “For the first time, we managed to distinguish these paths and select the reaction we want.”

Coincidence momentum imaging was used to detect ionic fragments.

The work is published in Physical Review X (doi: 0.1103/PhysRevX.4.021005).

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