When nuclei catch up with electrons

April 17, 2018, ETH Zurich
In the AttoCOLTRIMS apparatus, the three-dimensional motion of electrons (blue elliptical arrow) and ions (H2+ and H+, grey arrows) can be detected in coincidence. The combination of an extreme-ultraviolet (XUV, blue) and a long and rather weak infrared (IR, red) pulse in a pump-probe set-up provides the basis for studying the attosecond dynamics of the H2 molecule. Credit: Ultrafast Laser Physics group, ETH Zurich

In an attosecond study of the H2 molecule, physicists at ETH Zurich found that for light atomic nuclei, as contained in most organic and biological molecules, the correlation between electronic and nuclear motions cannot be ignored.

The main goal in science is understanding the dynamics of quantum-mechanical systems on their natural timescale. Molecules, are among the most interesting systems to investigate, having a very high degree of complexity, particularly when compared to . The few attosecond experiments performed on to date have provided valuable insight into electron dynamics. In these studies, the dynamics of the nuclei around which the electrons evolve was assumed to be "frozen," given that nuclei are much heavier than electrons and therefore move more slowly. However, even in the attosecond time regime, the approximation that electronic and nuclear motion are decoupled from one another is often unjustified. In particular, in molecules composed of light atomic species, the nuclear motion can be as fast as , resulting in a strong coupling between the two.

A team led by Dr. Laura Cattaneo and Prof. Ursula Keller in the Department of Physics at ETH Zurich has now studied the lightest and smallest of all molecules, H2, and explored what happens when nuclear and electronic occur on a comparable time scale. As they report in an article published today in Nature Physics, they found that in molecules, delays can significantly depend on the kinetic energy of both the photoelectron and the nuclei. (Ionization delays are the time between the absorption of a photon and the emission of an electron during photoionization.) This finding extends the concept of ionization delays introduced for atomic systems. Variations of ionization delays with nuclear kinetic energy can be as large as variations with electronic . This implies that whenever light atoms are involved in the molecular ionization process, the outgoing electron wave packet cannot be disentangled from the nuclear wave packet.

These measurements at the attosecond timescale are based on an experimental approach developed earlier in the Keller group. In the so-called AttoCOLTRIMS apparatus (see the figure), attosecond metrology is combined with the imaging technique COLTRIMS, in which the correlated properties of the fragments of a molecular reaction can be recorded. This experimental capability was combined with nearly exact ab initio theory, performed by collaborators at the Universidad Autonoma de Madrid (Spain), to describe both electronic and nuclear motions, as well the coupling between them.

The significance of this work goes well beyond the simple H2 molecule. Hydrogen atoms are present in most organic and biologically relevant molecules. Understanding the effects and contributions from coupled electron and nuclear dynamics present in such systems should therefore provide fundamental insight that will be important in various fields of research.

Explore further: A milestone in petahertz electronics

More information: L. Cattaneo et al, Attosecond coupled electron and nuclear dynamics in dissociative ionization of H2, Nature Physics (2018). DOI: 10.1038/s41567-018-0103-2

Related Stories

A milestone in petahertz electronics

March 13, 2018

In a semiconductor, electrons can be excited by absorbing laser light. Advances in the past decade have enabled measuring this fundamental physical mechanism on timescales below a femtosecond (10-15 s). Now, physicists at ...

Attoseconds break into atomic interior

February 27, 2018

A newly developed laser technology has enabled physicists in the Laboratory for Attosecond Physics (jointly run by LMU Munich and the Max Planck Institute of Quantum Optics) to generate attosecond bursts of high-energy photons ...

Physicists publish new findings on electron emission

September 21, 2017

Even more than 100 years after Einstein's explanation of photoemission the process of electron emission from a solid material upon illumination with light still poses challenging surprises. In the report now published in ...

Recommended for you

Magnetoresistance ratio enhancement in Heusler-based alloy

December 18, 2018

Magnetic field sensors can enhance applications that require efficient electric energy management. Improving magnetic field sensors below the picoTesla range could enable a technique to measure brain activity at room temperature ...

1 comment

Adjust slider to filter visible comments by rank

Display comments: newest first

holoman
not rated yet Apr 17, 2018
Might like.

electron coupled plasma with atomic mass filter

https://thomasins...out.html

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.