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Collisions of room temperature helium with ultra-cold lithium and the van-der-Waals bound state of HeLi



Constantinos Makrides, Daniel Barker, James A. Fedchak, Julia Scherschligt, Stephen Eckel, Eite Tiesinga


We have computed the thermally-averaged total, elastic rate coefficient for the collision of a room-temperature helium atom with an ultra-cold lithium atom. This rate coefficient has been computed as part of the characterization of a cold atom vacuum sensor based on laser-cooled Li atoms that will operate in the Ultra-High-Vacuum (UHV, p < 10^-6 Pa) and Extreme- High-Vacuum (XHV, p < 10^-10 Pa) regimes. The analysis involves computing the X HeLi Born-Oppenheimer potential followed by the numerical solution of the relevant radial Schrodinger equation. The potential is computed using a multi-reference-coupled-cluster electronic-structure method with basis sets of different completeness in order to characterize our uncertainty budget. We predict that the rate coefficient for a 300 K helium gas and a 1 microK Li gas is 1.467(13)×10^-9 cm^3 /s for ^4He+^6Li and 1.471(13) × 10^-9 cm^3 /s for ^4He+^7Li, where the numbers in parenthesis are the one-standard-deviation uncertainties in the last two significant digits. We quantify the temperature dependence as well. Finally, we evaluate the binding of the single van-der-Waals bound state of HeLi. We predict that this weakly-bound level has a binding energy of -0.0064(43) x hc cm^-1 and -0.0122(67) x hc cm^-1 for ^4He^6Li and ^4He^7Li, respectively.
Physical Review A


pressure sensor, ultracold atoms, van-der-Waals molecules, interatomic potentials, UHV


Makrides, C. , Barker, D. , Fedchak, J. , Scherschligt, J. , Eckel, S. and Tiesinga, E. (2020), Collisions of room temperature helium with ultra-cold lithium and the van-der-Waals bound state of HeLi, Physical Review A, [online],, (Accessed May 24, 2024)


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Created January 5, 2020, Updated October 12, 2021