Using ions to find molecules

Date:
March 11, 2022
Source:
Universiteit van Amsterdam
Summary:
When we think of ions, we usually think of single atoms that
have lost or gained some electrons, but entire molecules can also
become ions.

Physicists now show that cold molecular ions can be created using
a new method, and that they are a very useful tool for detecting
small amounts of other, regular molecules.



FULL STORY ==========================================================================
When we think of ions, we usually think of single atoms that have lost
or gained some electrons, but entire molecules can also become ions. In
a new publication that was highlighted as an Editor's Suggestion in
Physical Review Letters this week, physicists from the University of
Amsterdam, QuSoft and Stony Brook University, show that cold molecular
ions can be created using a new method, and that they are a very useful
tool for detecting small amounts of other, regular molecules.


========================================================================== Trapped ions An ion is an atom or molecule with a surplus or shortage
of electrons. Being charged particles, ions can be 'trapped'
by electromagnetic fields: it is easy to keep them in a fixed
position. Trapped ions constitute a promising platform for quantum
computation. The reason for this is that they can be stored for a long
time, and that modern lasers allow physicists to control single ions very precisely. These properties also make trapped ions into prime candidates
to study chemical reactions, especially when they are immersed in a bath
of regular atoms or molecules.

In many physics experiments, it is useful to study particles that are
extremely cold -- simply because cold particles move slower and vibrate
less, so there is less 'noise' in the experiment. So far, ion-molecule
studies have been limited to cold molecules with temperatures around 1
kelvin (i.e. one degree above the absolute zero temperature), but the
hybrid ion-atom experiment at the University of Amsterdam now uses
molecules with temperatures of only a few millionths of a kelvin,
studying the coldest ion-molecule collisions in the world.

Physicists led by Rene Gerritsma from the UvA-Institute of Physics and
QuSoft in collaboration with Arghavan Safavi-Naini (UvA/QuSoft) and Jesus Pe'rez-Ri'os (Stony Brook University), measured the molecular ion created
in a chemical reaction where lithium molecules (Li2) and atomic ytterbium
ions (Yb+) turn into lithium atoms (Li) and molecular lithium-ytterbium
ions (LiYb+). They were able to use this chemical reaction to sense very
small amounts of molecules.

Their results were published in the journal Physical Review Letters
this week.

Ultracold gases Besides their numerous other uses, such as their use in extremely precise clocks and quantum simulations of many-body systems, ultracold gases can also be used to create cold molecules. Using a
technique called magneto-association, so-called Feshbach dimers can be
created from an ultracold gas -- molecules that are as cold as the gas
that their parts came from. Combining these molecules with a single
trapped ion, IoP physicists Henrik Hirzler, Rianne Lous and Eleanor
Trimby observed for the first time ion-molecule chemical reactions with ultracold molecules.

The researchers observed that collisions between a single ion and
a Feshbach dimer led to the formation of the molecular ion mentioned
above, where one of the molecules' atoms gets stuck to the ion. Looking
at the fluorescence of the ion, the formation of the molecular ion can
be observed by seeing the fluorescence go dark, a result of the fact that
the molecular ion has energy levels that differ from those of the atomic
ion. The presence of the molecular ion was also confirmed by measuring
the frequency with which it resonates in the ion trap, a frequency that
differs for the heavier molecular particles.

Additional measurements revealed that in fact every ion-molecule collision resulted in the formation of a molecular ion.

A useful reaction The group then found that their methods were very
sensitive: they could use the reaction Li2 +Yb+ -> LiYb+ + Li to detect
only about 50 molecules in a cloud of 20,000 atoms. For such trace amounts
of molecules, normal imaging techniques typically fail. Therefore,
the ion could be used as a much better sensor for the molecules. This
result is a first step towards being able to probe quantum states of
matter with only a single ion as a detector.

The observed cold chemical reaction also points to a new method to get
cold and controllable molecular ions. Those are especially interesting
for precision spectroscopy and for a better understanding of ultracold collisions and chemistry.


========================================================================== Story Source: Materials provided by Universiteit_van_Amsterdam. Note:
Content may be edited for style and length.


========================================================================== Journal Reference:
1. H. Hirzler, R. S. Lous, E. Trimby, J. Pe'rez-Ri'os,
A. Safavi-
Naini, R. Gerritsma. Observation of Chemical Reactions between a
Trapped Ion and Ultracold Feshbach Dimers. Physical Review Letters,
2022; 128 (10) DOI: 10.1103/PhysRevLett.128.103401 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2022/03/220311115352.htm

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