My watch list  

Steering chemical reactions with laser pulses


TU Wien

Laser amplifier, used to create intense ultra-short pulses

TU Wien

Short laser pulses interacting with ethylene

Usually, chemical reactions just take their course, much like a ball rolling downhill. However, it is also possible to deliberately control chemical reactions: at the Vienna University of Technology, molecules are hit with femtosecond laser pulses, changing the distribution of electrons in the molecule. This interaction is so short that at first it does not have any discernable influence on the atomic nuclei, which have much more mass than the electrons. However, the disturbance of the electron distribution can still initiate chemical processes and eventually separate the nuclei from each other. The properties of the laser pulse determine which chemical final products are created.

Controlling chemistry

Chemists can choose which molecules they want to take part in a chemical reaction – but the result is usually determined by the physical and chemical properties of molecules and by external parameters such as the temperature. The reaction itself cannot be controlled. Researchers at the Vienna University of Technology (Photonics Institute) have now succeeded in directly inducing the splitting of hydrocarbons such as ethylene (C2H4) or acetlyene (C2H2) into smaller fragments.

“We are using two different laser pulses”, says Markus Kitzler (TU Vienna). “The first pulse takes about 50 femtoseconds and makes the molecules rotate at different speeds.” After some time, all molecules are approximately aligned - and then the second laser pulse is applied, which only lasts for five femtoseconds, less than two oscillations of the light wave. This pulse changes the state of the electrons; it can even remove electrons from the molecule.

Selecting a reaction path

Electrons weigh much less than atomic nuclei. Therefore the electrons can be influenced dramatically by the laser pulse, whereas the heavier nuclei are much too inert for any observable motion in this short period of time. If, however, exactly the right electrons are removed from the molecule, the molecule can be made to break at a specific position. That way, acetylene (C2H2) can be broken up into CH2+, CH+, or carbon ions (C+). “Various reaction paths are possible. For the first time, we managed to distinguish these paths and select the reaction we want”, says Markus Kitzler.

An extremely short laser pulse – five femtoseconds (5.10^(-15) seconds) are just five millionths of a billionth of a second – initiates a chemical process, which takes place on a much larger timescale. This is similar to a short explosion at precisely the right places, which may cause a huge building to sway and eventually collapse.

The composition of chemical end products can be controlled by a number of different parameters: The alignment of the molecules by the first laser pulse, the duration and the intensity of the second pulse, which ionizes the molecules.

The experiments were done by Markus Kitzler’s research team, his postdoc Xinhua Xie played a leading role in data analysis. Katharinia Doblhoff-Dier and Prof. Stefanie Gräfe from Jena University and Erik Lötstedt, from Tokyo University contributed model calculations, which were invaluable for the interpretation of the experimental results.

The experimental results have now been published in two scientific publications: In “Physical Review Letters” and “Physical Review X”.


Facts, background information, dossiers
  • acetylene
  • TU Wien
More about TU Wien
  • News

    The Beam of Invisibility: New cloaking technology has been developed

    How do we make an object invisible? Researchers from TU Wien (Vienna), together with colleagues from Greece and the USA, have now developed a new idea for a cloaking technology. A completely opaque material is irradiated from above with a specific wave pattern – with the effect that light w ... more

    Microprocessors based on a layer of just three atoms

    Two-dimensional materials, or 2D materials for short, are extremely versatile, although - or often more precisely because - they are made up of just one or a few layers of atoms. Graphene is the best-known 2D material. Molybdenum disulphide (a layer consisting of molybdenum and sulphur atom ... more

    Diamonds coupled using quantum physics

    Diamonds with minute flaws could play a crucial role in the future of quantum technology. For some time now, researchers at TU Wien have been studying the quantum properties of such diamonds, but only now have they succeeded in coupling the specific defects in two such diamonds with one ano ... more

  • Videos

    Epoxy Resin

    A flash of ultraviolet light sets off a chain reaction which hardens the whole object. more


    The coating machine Noreia was built at TU Wien. This time-lapse video shows the construction process. more

    Shaping Drops: Control over Stiction and Wetting

    Some surfaces are wetted by water, others are water-repellent. TU Wien (Vienna), KU Leuven and the University of Zürich have discovered a robust surface whose adhesive and wetting properties can be switched using electricity. This remarkable result is featured on the cover of Nature magazin ... more

Your browser is not current. Microsoft Internet Explorer 6.0 does not support some functions on Chemie.DE