Caffeine offers clues to ultra-transient positive charges' migration

July 5, 2018, Springer

Caffeine keeps physicists up at night. Particularly those concerned with the capacity of electrons to absorb energy. In a new study published in EPJ B, a Franco-Japanese team of physicists have used the caffeine molecule as a playground to test the effect of ionising radiation on its electrons as they approach excited states. Their model accounts for the ionisation phenomenon in electrons, which are in a site-specific, localised orbit in the caffeine molecule. The electron excitation leaves the door open to positive charge progression along a molecular backbone. Thomas Niehaus from Claude Bernard Lyon 1 University, France, and colleagues have now developed a method for quantifying this positive charge migration in line with the ultra-short laser impulse. The observed charge motion happens on an attosecond time scale charge rearrangements driven by nuclear motion.

In this study, the authors rely on time-dependent , which is typically used as a computer-based characterisation tool to determine the width of wavelength in which a molecule absorbs radiation. It is also used to investigate electric charge transfer in photovoltaic and energy conversion materials. Lastly, it can be used for the real-time observation of electrical carrier dynamics in solids.

Since the advent of ultra-short sources—which operate in the attosecond range—this theory can now be put to the test experimentally. This is because the in which energy absorption by electrons takes place now persists long enough to be observed in experiments. Chemical reactions occurring at specific sites in the molecule are difficult to realise with longer laser pulses because the heat quickly destroys all site-specific information imprinted by the laser pulse.

The authors find that the observed dynamics for positive charges alongside the backbone of the caffeine molecule depend on the timing of the laser pulse. What is more, the dynamics of the positive charges' migration is governed by the fact that they are inter-related and by the complex interplay between several ionisation channels.

Explore further: The pho­to­elec­tric ef­fect in stereo

More information: Thomas A. Niehaus et al, Pulse shape and molecular orientation determine the attosecond charge migration in Caffeine, The European Physical Journal B (2018). DOI: 10.1140/epjb/e2018-90223-5

Related Stories

The pho­to­elec­tric ef­fect in stereo

June 22, 2018

In the photoelectric effect, a photon ejects an electron from a material. Researchers at ETH have now used attosecond laser pulses to measure the time evolution of this effect in molecules. From their results they can deduce ...

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 ...

The world's shortest laser pulse

October 27, 2017

ETH researchers succeeded in shortening the pulse duration of an X‑ray laser to only 43 attoseconds. With a time resolution in the range of a few quintillionths of a second, they are now able for the first time to observe ...

Processes in the atomic microcosmos revealed

May 16, 2018

Physicists at Friedrich-Alexander-Universität Erlangen-Nürnberg (FAU) have successfully generated controlled electron pulses in the attosecond range. They used optical traveling waves formed by laser pulses of varying wavelengths. ...

Scientists track electrons in molecules

June 13, 2010

(PhysOrg.com) -- Physicists in Europe have successfully glimpsed the motion of electrons in molecules. The results are a major boon for the research world. Knowing how electrons move within molecules will facilitate observations ...

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 ...

Recommended for you

Researchers study interactions in molecules using AI

October 19, 2018

Researchers from the University of Luxembourg, Technische Universität Berlin, and the Fritz Haber Institute of the Max Planck Society have combined machine learning and quantum mechanics to predict the dynamics and atomic ...

Pushing the extra cold frontiers of superconducting science

October 18, 2018

Measuring the properties of superconducting materials in magnetic fields at close to absolute zero temperatures is difficult, but necessary to understand their quantum properties. How cold? Lower than 0.05 Kelvin (-272°C).

The big problem of small data: A new approach

October 18, 2018

Big Data is all the rage today, but Small Data matters too! Drawing reliable conclusions from small datasets, like those from clinical trials for rare diseases or in studies of endangered species, remains one of the trickiest ...

0 comments

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.