Vibrational quenching of the electronic ground state in ThO in cold collisions withHe3

Abstract

We measure the ratio $\ensuremath{\gamma}$ of the momentum transfer--to--vibrational quenching cross section for molecular thorium monoxide (ThO) [$X{(}^{1}{\ensuremath{\Sigma}}^{+})$, $v=1$, $J=0$] in collisions with atomic helium between 800 mK and 2.4 K. We find $\ensuremath{\gamma}\ensuremath{\sim}{10}^{4}$. We also observe indirect evidence for ThO-He van der Waals complex formation, which has been predicted by theory [Tscherbul, Sayfutyarova, Buchachenko, and Dalgarno, J. Chem. Phys. 134, 144301 (2011)], and in conjunction, we determine the three-body recombination rate constant at 2.4 K, ${\ensuremath{\Gamma}}_{3}=8\ifmmode\pm\else\textpm\fi{}2\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}33}$ ${\mathrm{cm}}^{6}$ ${\mathrm{s}}^{\ensuremath{-}1}$.