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Chemical reaction control at the quantum level (PENNING)

Chemical reaction control at the quantum level (PENNING)


On a macroscopic level, chemical reaction control plays an important role in drug discovery, where the production of unwanted or potentially hazardous side products must be avoided. In this case, reactions are commonly controlled by changing the temperature, pressure or by using different catalysts. These approaches cannot be directly transferred to the microscopic level, where single atoms and molecules interact. In this regime, electromagnetic fields can be used to precisely tune the yield of certain products or to suppress the production of unwanted ones. Experiments in this purely quantum-mechanical regime are intriguing, because they allow us to study the influence of quantum effects, such as barrier tunnelling, on chemical reactivity. In order to achieve reaction control in the quantum regime, our current work aims at understanding the mechanistic details of reactive collisions.
In our current experiments, we focus on collisions between long-lived excited-state (metastable) helium atoms (He*) and lithium atoms (Li) [1]. The outcome of this chemi-ionization process can be twofold:

Penning reaction pathways

Owing to the simple and well-known internal energy-level structure of the two atoms, they can be prepared in a variety of initial quantum states. This allows us to precisely investigate quantum-state dependent effects on the reactivity, such as the influence of the mutual electron spin direction.

We make use of two different techniques to prepare the reaction partners. The Li atoms are cooled by laser radiation and captured in a magneto-optical trap (MOT) at a temperature of around 1 mK. A beam of He* atoms is created by expanding He gas into the vacuum using a pulsed valve and by exciting it using a gas discharge. The reaction rate is measured by counting the number of ions produced during the collision process.

Our lab hosts five different narrowband, continuous-wave laser systems with wavelengths ranging from the blue (at 397 nm) to the infrared (at 1083 nm). These systems are used for the laser cooling of Li and for the preparation of different quantum states prior to the collision [2].

Laser en

Laser system for Li laser cooling

photograph of the experimental chamber

Experimental chamber

Our lab

Photograph of the entire laboratory


Relevant publications:

[10] Dulitz K, Sixt T, Guan J, Grzesiak J, Debatin M, Stienkemeier F
Suppression of Penning ionization by orbital angular momentum conservation
Phys Rev A, 2020; 102: 022818-1-022818-7.: abstract - pdf - arXiv

[9] Dulitz K, van den Beld-Serrano M, Stienkemeier F
Single-Source, Collinear Merged-Beam Experiment for the Study of Reactive Neutral-Neutral Collisions
J. Phys. Chem. A 2020, 124, 17, 3484–3493: abstract - pdf

[8] Guan J, Behrendt V, Shen P, Hofsäss S, Muthu-Arachchige T, Grzesiak J, Stienkemeier F, Dulitz K:
Optical Quenching of Metastable Helium Atoms using Excitation to the 4P State
Appl Phys Rev, 2019; 11 (5): 054073-1-054073-8.: abstract - pdf - arXiv

[7] Grzesiak J, Momose T, Stienkemeier F, Mudrich M, Dulitz K:
Penning collisions between supersonically expanded metastable He atoms and laser-cooled Li atoms
J Chem Phys, 2019; 150 (3): 034201-1-034201-9.: abstract - pdf - arXiv

[6] Grzesiak J, Vashishta M, Djuricanin P, Stienkemeier F, Mudrich M, Dulitz K, Momose T:
Production of rotationally cold methyl radicals in pulsed supersonic beams
Rev Sci Instrum, 2018; 89 (11): 113103-1-113103.6.: abstract - pdf - arXiv

[5] Toscano J, Tauschinsky A, Dulitz K, Rennick C J, Heazlewood B R, Softley T P:
Zeeman deceleration beyond periodic phase space stability
New J Phys, 2017; 19: 083016.: abstract - pdf

[4] Strebel M, Müller T O, Ruff B, Stienkemeier F, Mudrich M:
Quantum rainbow scattering at tunable velocities
Phys Rev A, 2012; 86 (6): 062711-1-062711-4.: abstract - pdf - arXiv

[3] Bobbenkamp R, Loesch H, Mudrich M, Stienkemeier F:
The excitation function for Li+HF-->LiF+H at collision energies below 80 meV
J Chem Phys, 2011; 135 (20): 204306-1-204306-8.: abstract - pdf - arXiv

[2] Strebel M, Spieler M, Stienkemeier F, Mudrich M:
Guiding slow polar molecules with a charged wire
Phys Rev A, 2011; 84 (5): 053430-1-053430-8.: abstract - pdf - arXiv

[1] Strebel M, Stienkemeier F, Mudrich M:
Improved setup for producing slow beams of cold molecules using a rotating nozzle
Phys Rev A, 2010; 81 (3): 033409-1-033409-12.: abstract - pdf - arXiv



Dr. Katrin Dulitz, katrin.dulitz[at]



Deutsche Forschungsgemeinschaft

International Research Training Group (IRTG 2079) "Cold Controlled Ensembles in Physics and Chemistry"

Fonds der Chemischen Industrie

Research Innovation Fund (University of Freiburg)

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