Observation of cold dipolar collisions between centrifuge decelerated molecules

Understanding molecular collisions at low energies is a prerequisite for future sympathetic and evaporative cooling of naturally occurring molecules. However, experimental investigation of collisions in this temperature regime is still in its infancy. Our cryofuge setup, the combination of cryogenic buffer gas cooling and centrifuge deceleration $\footnote{S. Chervenkov et al., \textbf{Phys. Rev. Lett.} 112, 013001 (2014)}$, produces slow molecular beams with densities of over $10^{9}/cm^{3}$. This allowes the observation of cold molecule-molecule collisions with large observed cross sections $> 10^{-12} cm^{2}$ for $CH_3F$ and $ND_3$ $\footnote{X. Wu et al., \textbf{Science} 358, 645-648, (2017)}$. Our experimental findings agree with theoretically modeled elastic and inelastic collisional loss rates. The low absolute velocity enables the straightforward loading of molecules into an electrostatic trap $\footnote{B.G.U. Englert et al., \textbf{Phys. Rev. Lett.} 107, 263003 (2011)}$ making much more detailed studies possible due to longer interaction times. Such measurements are important, e.g., for future evaporative cooling experiments.