Production of cold beams of ND3 with variable rotational state distributions by electrostatic extraction of He and Ne buffer-gas-cooled beams

Twyman, Kathryn S.; Bell, Martin T.; Heazlewood, Brianna R.

doi:10.1063/1.4885855

Cited by 20 publications

(25 citation statements)

References 32 publications

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“…4 The simulated translational temperature of NH 3 equilibrates to 5 ± 1 K at cell lengths of 2 mm and longer. This is in agreement with the experimental buffer-gas-cooled ND 3 translational temperature of 5.96 ± 0.05 K, measured at the end of the quadrupole guide, 16 and with the 6.0 K He buffer gas. The uncertainty in the NH 3 translational temperature primarily arises from the uncertainty in the fit of the velocity distribution to the simulated particles.…”

Section: A Rotational and Translational Energy Distributionssupporting

confidence: 78%

“…16, the 20 × 40 × 40 mm (length × height × width) buffer gas cell in the experimental setup is attached to the second stage of a two stage pulse-tube cryocooler.The buffer gas inlet pressure is typically maintained at 0.6 mbar, with an ammonia inlet flow rate of 1.0 SCCM. Helium enters the buffer gas cell at 6 K, as the buffer gas line thermalises with each cryocooler stage prior to entering the buffer gas cell.…”

Section: Modelling An Experimental Buffer Gas Cellmentioning

confidence: 99%

“…16 The quadrupole is assembled from hand-polished stainless steel rods with a 2 mm diameter circular cross section. Voltages of up to ±5 kV are applied to the guide electrodes, achieving maximal field strengths of up to 90 kV/cm at the electrode surfaces.…”

Section: Modelling An Experimental Buffer Gas Cellmentioning

confidence: 99%

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Using a direct simulation Monte Carlo approach to model collisions in a buffer gas cell

Doppelbauer

Schullian

Loreau

et al. 2017

The Journal of Chemical Physics

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A direct simulation Monte Carlo (DSMC) method is applied to model collisions between He buffer gas atoms and ammonia molecules within a buffer gas cell. State-to-state cross sections, calculated as a function of the collision energy, enable the inelastic collisions between He and NH 3 to be considered explicitly. The inclusion of rotational-state-changing collisions affects the translational temperature of the beam, indicating that elastic and inelastic processes should not be considered in isolation. The properties of the cold molecular beam exiting the cell are examined as a function of the cell parameters and operating conditions; the rotational and translational energy distributions are in accord with experimental measurements. The DSMC calculations show that thermalisation occurs well within the typical 10-20 mm length of many buffer gas cells, suggesting that shorter cells could be employed in many instances-yielding a higher flux of cold molecules.

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Section: A Rotational and Translational Energy Distributionssupporting

confidence: 78%

Section: Modelling An Experimental Buffer Gas Cellmentioning

confidence: 99%

See 1 more Smart Citation

Using a direct simulation Monte Carlo approach to model collisions in a buffer gas cell

Doppelbauer

Schullian

Loreau

et al. 2017

The Journal of Chemical Physics

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“…Several techniques for state detection of cold molecules have been used so far [34,35,36,37,38,39,40]. Among them, depletion methods, as adopted in previous experiments carried out by our group [35,40], are particularly advantageous since they are applicable to a large range of molecules and avoid the difficulties of the light-induced fluorescence (LIF) and resonance-enhanced multi-photon ionization (REMPI) detection techniques.…”

Section: Methods For Rotational-state Detectionmentioning

confidence: 99%

Thermometry of Guided Molecular Beams from a Cryogenic Buffer‐Gas Cell

Gantner

Zeppenfeld

et al. 2016

ChemPhysChem

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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

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“…In previous studies, such cryogenic effusive sources have been shown to produce, given the right settings, hydrodynamically enhanced, cold molecular beams [62][63][64][65][66]. These beams provide high-density, continuous beams with translational and rotational temperatures in the range of a few Kelvin.…”

Section: General Experimental Considerationsmentioning

confidence: 99%

Merged neutral beams

Osterwalder

2015

EPJ Techn Instrum

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A detailed description of a merged beam apparatus for the study of low energy molecular scattering is given. This review is intended to guide any scientist who plans to construct a similar experiment, and to provide some inspiration in describing the approach we chose to our goal. In our experiment a supersonic expansion of paramagnetic particles is merged with one of polar molecules. A magnetic and an electric multipole guide are used to bend the two beams onto the same axis. We here describe in detail how the apparatus is designed, characterised, and operated.Keywords: Cold molecules; Low energy scattering; Molecular beams; Cold chemistry ReviewIn the last 15 years several methods have been developed to prepare molecular samples at temperatures well below 1 K and to completely control their translational degrees of freedom [1][2][3][4]. A particular area where this is of interest is the study of molecular collisions, and cold chemistry [4][5][6][7][8][9][10][11]. Ultracold molecules, produced by joining two atoms at very low temperature, enabled the investigation of molecular collisions at temperatures as low as 1 μK [12][13][14]. These methods are ideally suited to study alkali dimers, but in order to access broader classes of molecules and a larger range of temperatures a different approach was necessary. The present paper describes such an approach, namely the merging of two molecular beams with controlled velocity.One of the most important developments for reaction dynamics studies in the twentieth century was the crossed-beam technique, for which a Nobel prize was awarded in 1986. In this experiment two molecular beams [15] are crossed to enable a highly detailed investigation of gas-phase molecular scattering, and in particular the measurement of state-to-state differential cross sections [16,17]. The high velocities of supersonic expansions and the crossing angle of usually 90 degrees make the crossed beam technique ideal for studies at high collision energies (E/k B 100 K, where k B is the Boltzmann constant). Lower energies are not accessible without special modifications, thus making the method blind to some of the most fundamental quantum mechanical effects in molecular scattering.The collision energy in a crossed beam experiment depends on the relative velocity of the two reactants. In any molecular collision event the energetics are given only by the motion in the molecular frame of reference (MFR), but not that of the centre of mass (CM). This is illustrated in Fig. 1. Panel A shows the position vectors for reactants 1 and 2

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Production of cold beams of ND3 with variable rotational state distributions by electrostatic extraction of He and Ne buffer-gas-cooled beams

Cited by 20 publications

References 32 publications

Using a direct simulation Monte Carlo approach to model collisions in a buffer gas cell

Using a direct simulation Monte Carlo approach to model collisions in a buffer gas cell

Thermometry of Guided Molecular Beams from a Cryogenic Buffer‐Gas Cell

Merged neutral beams

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