Producing large samples of slow molecules from thermal-velocity ensembles is a formidable challenge. Here we employ a centrifugal force to produce a continuous molecular beam with a high flux at near-zero velocities. We demonstrate deceleration of three electrically guided molecular species, CH3F, CF3H, and CF3CCH, with input velocities of up to 200  m s(-1) to obtain beams with velocities below 15  m s(-1) and intensities of several 10(9)  mm(-2) s(-1). The centrifuge decelerator is easy to operate and can, in principle, slow down any guidable particle. It has the potential to become a standard technique for continuous deceleration of molecules.

Ultracold molecules represent a fascinating research frontier in physics and chemistry, but it has proven challenging to prepare dense samples at low velocities. Here, we present a solution to this goal by means of a nonconventional approach dubbed cryofuge. It uses centrifugal force to bring cryogenically cooled molecules to kinetic energies below 1 K × in the laboratory frame, where is the Boltzmann constant, with corresponding fluxes exceeding 10 per second at velocities below 20 meters per second. By attaining densities higher than 10 per cubic centimeter and interaction times longer than 25 milliseconds in samples of fluoromethane as well as deuterated ammonia, we observed cold dipolar collisions between molecules and determined their collision cross sections.

Abstract.We present a comprehensive characterization of cold molecular beams from a cryogenic buffer-gas cell, providing an insight into the physics of buffer-gas cooling. Cold molecular beams are extracted from a cryogenic cell by electrostatic guiding, which is also used to measure their velocity distribution. Molecules' rotational-state distribution is probed via radio-frequency resonant depletion spectroscopy. With the help of complete trajectory simulations, yielding the guiding efficiency for all of the thermally populated states, we are able to determine both the rotational and the translational temperature of the molecules at the output of the buffer-gas cell. This thermometry method is demonstrated for various regimes of buffer-gas cooling and beam formation as well as for molecular species of different sizes, CH 3 F and CF 3 CCH. Comparison between the rotational and translational temperatures provides evidence of faster rotational thermalization for the CH 3 F-He system in the limit of low He density. In addition, the relaxation rates for different rotational states appear to be different.2

Cryogenic buffer gas cells have been a workhorse for the cooling of molecules in the last decades. The straightforward sympathetic cooling principle makes them applicable to a huge variety of different species. Notwithstanding this success, detailed simulations of buffer gas cells are rare, and have never been compared to experimental data in the regime of low to intermediate buffer gas densities. Here, we present a numerical approach based on a trajectory analysis, with molecules performing a random walk in the cell due to collisions with a homogeneous buffer gas. This method can reproduce experimental flux and velocity distributions of molecules emerging from the buffer gas cell for varying buffer gas densities. This includes the strong decrease in molecule output from the cell for increasing buffer gas density and the so-called boosting effect, when molecules are accelerated by buffer-gas atoms after leaving the cell. The simulations provide various insights which could substantially improve buffer-gas cell design. arXiv:2001.07759v1 [physics.chem-ph] 21 Jan 2020Buffer-gas cooling of molecules in the low-density regime

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Die Zentrifugal‐ oder Fliehkraft wird normalerweise mit Beschleunigung in Verbindung gebracht. Unsere Gruppe am Max‐Planck‐Institut für Quantenoptik hat kürzlich gezeigt, dass bei richtiger Dosierung dieselbe Kraft auch zum Abbremsen von Molekülen verwendet werden kann.

The Back Cover picture depicts a robust thermometry method for a comprehensive characterization of the rotational and translational cooling of polyatomic molecules from a cryogenic buffer‐gas cell, based on resonant radio‐frequency depletion spectroscopy. More information can be found in the Full Paper by S. Chervenkov and co‐workers on page 3631 in Issue 22, 2016 (DOI:10.1002/cphc.201600559).