Equilibrium Thermodynamic Properties, Structure and Dynamics of the Lithium Helium (LiHe) van der Waals Molecule

Abstract

Lithium helium (LiHe) is an interesting van der Waals molecule due to theoreticalinterest in its molecular structure and properties. We use cryogenic helium buer gascooling to produce high densities of atomic lithium at temperatures ranging from 1{5Kelvin. LiHe molecules are formed by three body recombination:Li + He + He $ LiHe + He: (1)The Li density is continuously monitored via laser absorption spectroscopy. LiHe isdetected spectroscopically using both laser induced uorescence and laser absorptionspectroscopy. The LiHe spectrum shows good agreement with a theoretical model ofthe molecular structure, with only a single bound rovibrational state.In thermal equilibrium, the expected density of LiHe is given bynLiHe = nLi nHe h22kBT3=2e=kBT ; (2)where n is the density of the given species and is the binding energy of the singleLiHe bound state. Our data shows good agreement with this model, and we use itto determine the binding energy of the LiHe ground state. The measured bindingenergy is consistent with the calculated value. We also made attempts to measurethe rate coecients for the reactions of Eq. 1.