Electron movements in liquid measured in super-slow motion

Date:
August 21, 2020
Source:
ETH Zurich
Summary:
Electrons are able to move within molecules, for example when
they are excited from outside or in the course of a chemical
reaction. For the first time, scientists have now succeeded in
studying the first few dozen attoseconds of this electron movement
in a liquid.



FULL STORY ==========================================================================
To understand how chemical reactions begin, chemists have been using
super-slow motion experiments for years to study the very first moments
of a reaction.

These days, measurements with a resolution of a few dozen attoseconds
are possible. An attosecond is 1x10^-18 of a second, i.e. a millionth
of a millionth of a millionth of a second.


==========================================================================
"In these first few dozen attoseconds of a reaction, you can already
observe how electrons shift within molecules," explains Hans Jakob
Wo"rner, Professor at the Laboratory of Physical Chemistry at ETH
Zurich. "Later, in the course of about 10,000 attoseconds or 10
femtoseconds, chemical reactions result in movements of atoms up to
and including the breaking of chemical bonds." Five years ago, the ETH professor was one of the first scientists to be able to detect electron movements in molecules on the attosecond scale. However, up to now such measurements could be carried out only on molecules in gaseous form
because they take place in a high-vacuum chamber.

Delayed transport of electrons from the liquid After building novel
measuring equipment, Wo"rner and his colleagues have now succeeded in
detecting such movements in liquids. To this end, the researchers made
use of photoemission in water: they irradiated water molecules with light, causing them to emit electrons that the scientists could then measure. "We chose to use this process for our investigation because it is possible to
start it with high temporal precision using laser pulses," Wo"rner says.

The new measurements also took place in high vacuum. Wo"rner and his
team injected a 25-micrometre-thin water microjet into the measuring
chamber. This allowed them to discover that electrons are emitted from
water molecules in liquid form 50-70 attoseconds later than from water molecules in vapour form.

The time difference is due to the fact that the molecules in liquid form
are surrounded by other water molecules, which has a measurable delay
effect on individual molecules.

Important step "Electron movements are the key events in chemical
reactions. That's why it's so important to measure them on a
high-resolution time scale," Wo"rner says.

"The step from measurements in gases to measurements in liquids is of particular importance, because most chemical reactions -- especially
the ones that are biochemically interesting -- take place in liquids."
Among those, there are numerous processes that, like photoemission in
water, are also triggered by light radiation. These include photosynthesis
in plants, the biochemical processes on our retina that enable us to see,
and damage to DNA caused by X-rays or other ionising radiation. With
the help of attosecond measurements, scientists should gain new insights
into these processes in the coming years.


========================================================================== Story Source: Materials provided by ETH_Zurich. Original written by
Fabio Bergamin. Note: Content may be edited for style and length.


========================================================================== Journal Reference:
1. Jordan I, Huppert M, Rattenbacher D, Peper M, Jelovina D, Perry
C, from
Conta A, sign A, Wo"rner HJ. Attosecond spectroscopy of liquid
water.

Science, 2020 DOI: 10.1126/science.abb0979 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2020/08/200821094900.htm

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