Complex pathways influence time delay in ionization of molecules
Date:
March 16, 2022
Source:
University of Freiburg
Summary:
Study shows how the mechanism of photoionization can be used to
gain insights into complex molecular potentials.
FULL STORY ==========================================================================
How can researchers use the mechanism of photoionization to gain insight
into complex molecular potential? This question has now been answered by
a team led by Prof. Dr. Giuseppe Sansone from the Institute of Physics
at the University of Freiburg. The researchers from Freiburg, the Max
Planck Institute for Nuclear Physics in Heidelberg and groups at the Universidad Autonoma in Madrid/ Spain and the University of Trieste/Italy
have published their results in the journal Nature Communications.
==========================================================================
In the origin of photoionization, also called the photoelectric effect,
an atom or molecule absorbs one quantum of light, usually indicated
as photon, from an external field. The energy absorbed in this process
is transferred to an electron, which is freed, leaving behind a singly
charged ion. In several aspects and for several applications, the effect
can be regarded as instantaneous, meaning that there is no significant
time delay between the absorption of the photon and the instant when
the electron is emitted. However, several experiments conducted in the
last years have evidenced that tiny, but measurable delays lying in the attosecond range (1 as=10-18 s) occur between these two processes.
Generation of attosecond pulses "Thanks to the advanced laser sources
and specially designed spectrometers available in our laboratory, we
can generate the shortest bursts of light, lasting only few hundreds
of attoseconds," Sansone explains. "Moreover, we can reconstruct the orientation of simple molecules when they absorb a photon from an external laser pulse. We have used such pulses to investigate the motion of the electrons after the absorption of a photon." Electrons experience paths
with potential peaks and valleys The researchers found that on its way
out from the molecule, the electron experiences a complex landscape characterized by potential peaks and valleys.
These are determined by the spatial distribution of the atoms composing
the system. The path followed by the electron during its motion can
affect the time it takes to be freed.
Extension to more complex molecular systems possible In the experiment,
the team measured the time delays accumulated by the electrons emitted
from CF4 molecules in different spatial directions were measured
using an attosecond pulse train combined with an ultrashort infrared
field. "Combining this information with the characterization of the
spatial orientation of the molecule, we can understand how the potential landscape and, in particular, potential peaks affect the time delay","
says the Freiburg physicist.
The work can be extended to more complex molecular systems and to
potentials changing on ultrashort timescales. In general, Sansone
emphasizes, this approach could give the possibility to map complex
potential landscapes from within, with unprecedented temporal resolution.
========================================================================== Story Source: Materials provided by University_of_Freiburg. Note:
Content may be edited for style and length.
========================================================================== Journal Reference:
1. H. Ahmadi, E. Ple'siat, M. Moioli, F. Frassetto, L. Poletto,
P. Decleva,
C. D. Schro"ter, T. Pfeifer, R. Moshammer, A. Palacios, F. Martin,
G.
Sansone. Attosecond photoionisation time delays reveal the
anisotropy of the molecular potential in the recoil frame. Nature
Communications, 2022; 13 (1) DOI: 10.1038/s41467-022-28783-x ==========================================================================
Link to news story:
https://www.sciencedaily.com/releases/2022/03/220316114955.htm
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