Title: Inelastic collisions of atomic thorium and molecular thorium monoxide with cold helium-3
Description: We measure inelastic cross sections for atomic thorium (Th) and molecular thorium monoxide (ThO) in collisions with $ 3$He at temperatures near 1 K. We determine the Zeeman relaxation cross section for Th ($ 3$F$_2$) to be $\sim 2 \times 10 {-17}$~cm$ {-2}$ at 800~mK. We study electronic inelastic processes in Th ($ 3$P$_0$) and find no quenching even after $10 6$ collisions at 800~mK. We measure the vibrational quenching cross section for ThO~(X,~$\nu=1$) to be $(7.9 \pm 2.7) \times 10 {-19}$~cm$ {-2}$ at 800~mK. Finally, we observe indirect evidence for ThO (X, $\nu=0$)--$ 3$He van der Waals complex formation, and measure the 3-body recombination rate constant to be $\Gamma_3 = (8 \pm 2) \times 10 {-33}$~cm$ 6$s$ {-1}$ at 2.4~K. The stability of the ground Th ($ 3$F$_2$) state, metastable Th ($ 3$P$_0$) state, and vibrational excited ThO (X, $\nu=1$) state provides data on anisotropic interactions in new systems and opens up the possibility for further studies and experiments, including trapping.