Low-energy molecular collisions in a permanent magnetic trap

TL;DR

This study demonstrates trapping of cold hydroxyl radicals using permanent magnets and measures their collision cross sections with helium and molecular deuterium at low energies, revealing energy-dependent inelastic collision behavior.

Contribution

It introduces a magnetic trapping method for cold OH radicals and provides the first measurements of their collision cross sections with He and D₂ at low energies.

Findings

Reduced inelastic cross sections below 84 cm$^{-1}$ for He--OH collisions.

Successful magnetic trapping of OH radicals at 70 mK.

Measured collision cross sections across a range of low energies.

Abstract

Cold, neutral hydroxyl radicals are Stark decelerated and confined within a magnetic trap consisting of two permanent ring magnets. The OH molecules are trapped in the ro-vibrational ground state at a density of $\sim10^{6}$ cm$^{-3}$ and temperature of 70 mK. Collisions between the trapped OH sample and supersonic beams of atomic He and molecular D$_{2}$ are observed and absolute collision cross sections measured. The He--OH and D$_{2}$--OH center-of-mass collision energies are tuned from 60 cm$^{-1}$ to 230 cm$^{-1}$ and 145 cm$^{-1}$ to 510 cm$^{-1}$, respectively, yielding evidence of reduced He--OH inelastic cross sections at energies below 84 cm$^{-1}$, the OH ground rotational level spacing.