A detailed account of the measurements of cold collisions in a molecular synchrotron

Abstract

We have recently demonstrated a general and sensitive method to study low energy collisions that exploits the unique properties of a molecular synchrotron (Van der Poel et al., Phys Rev Lett 120:033402, 2018). In that work, the total cross section for ND3 + Ar collisions was determined from the rate at which ammonia molecules were lost from the synchrotron due to collisions with argon atoms in supersonic beams. This paper provides further details on the experiment. In particular, we derive the model that was used to extract the relative cross section from the loss rate, and present measurements to characterize the spatial and velocity distributions of the stored ammonia molecules and the supersonic argon beams.

Cold and controlled chemical reaction dynamics

“…With a view to improving the sensitivity of merged beam experiments, a magnetic synchrotron has been proposed, 76 and an electric version has been developed. 77,78 Particles are confined in packets within the storage ring. The packets of particles traversing the ring can interact with a tangential supersonic beam multiple times (over numerous round trips), leading to an enhanced signal-to-noise ratio.…”

Molecular Collisions: from Near-cold to Ultra-cold

“…After m round trips, it would have interacted mn times. With an additional factor √ n due to summed intensity of the n packets, the total gain in sensitivity is mn √ n, which could amount to a factor of 100 -1000 [226].…”

Evolutionary Algorithm Optimization of Zeeman Deceleration: Is It Worthwhile for Longer Decelerators?

“…The decrease in rotational energy (and, to a lesser extent, vibrational energy) is compensated for by the increased kinetic energy of the beam in the laboratory frame. − Several methods have been adopted to mitigate the high forward velocities of supersonic beams to facilitate the study of reactions at low collision energies. One such approach involves the crossing of two supersonic beams at very shallow angles, such that the relative velocity of each beam is minimized; the velocity matching and merging of two beams at a zero crossing angle has been successfully demonstrated by several groups. − An alternative approach to merging two velocity-matched beams is to remove kinetic energy from a single supersonic beam before it encounters a target of trapped reactants …”