When nuclei catch up with electrons

April 16, 2018

Understanding the dynamics of quantum-mechanical systems on their natural time scale is the main goal in attosecond science. Among the most interesting systems to investigate are molecules, which have a very high degree of complexity, in particular when compared to atomic systems. So far, the few attosecond experiments performed on molecules 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 not justified. In particular in molecules composed of light atomic species, the nuclear motion can be as fast as electron dynamics, 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 motion happen on a comparable time scale. As they report in an article published today in Nature Physics, they found that in molecules ionization delays --- the time between the absorption of a photon and the emission of an electron during photoionization --- can significantly depend on the kinetic energy of both the photoelectron and the nuclei. This finding extends the concept of ionization delays introduced for atomic systems. Variations of ionization delays with the nuclear kinetic energy can be as large as variations with the electronic kinetic energy. 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 time scale 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 studied. 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.
-end-


ETH Zurich Department of Physics

Related Nuclear Articles from Brightsurf:

Explosive nuclear astrophysics
An international team has made a key discovery related to 'presolar grains' found in some meteorites.

Nuclear medicine and COVID-19: New content from The Journal of Nuclear Medicine
In one of five new COVID-19-related articles and commentaries published in the June issue of The Journal of Nuclear Medicine, Johnese Spisso discusses how the UCLA Hospital System has dealt with the pandemic.

Going nuclear on the moon and Mars
It might sound like science fiction, but scientists are preparing to build colonies on the moon and, eventually, Mars.

Unused stockpiles of nuclear waste could be more useful than we might think
Chemists have found a new use for the waste product of nuclear power -- transforming an unused stockpile into a versatile compound which could be used to create valuable commodity chemicals as well as new energy sources.

Six degrees of nuclear separation
For the first time, Argonne scientists have printed 3D parts that pave the way to recycling up to 97 percent of the waste produced by nuclear reactors.

How to dismantle a nuclear bomb
MIT team successfully tests a new method for verification of weapons reduction.

Material for nuclear reactors to become harder
Scientists from NUST MISIS developed a unique composite material that can be used in harsh temperature conditions, such as those in nuclear reactors.

Nuclear physics -- probing a nuclear clock transition
Physicists have measured the energy associated with the decay of a metastable state of the thorium-229 nucleus.

Milestones on the way to the nuclear clock
For decades, people have been searching for suitable atomic nuclei for building an ultra-precise nuclear clock.

Nuclear winter would threaten nearly everyone on Earth
If the United States and Russia waged an all-out nuclear war, much of the land in the Northern Hemisphere would be below freezing in the summertime, with the growing season slashed by nearly 90 percent in some areas, according to a Rutgers-led study.

Read More: Nuclear News and Nuclear Current Events
Brightsurf.com is a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for sites to earn advertising fees by advertising and linking to Amazon.com.