Skip to main content
U.S. flag

An official website of the United States government

Dot gov

The .gov means it’s official.
Federal government websites often end in .gov or .mil. Before sharing sensitive information, make sure you’re on a federal government site.


The site is secure.
The https:// ensures that you are connecting to the official website and that any information you provide is encrypted and transmitted securely.

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



Constantinos Makrides, Daniel S. Barker, James A. Fedchak, Julia K. Scherschligt, Stephen P. 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
Created January 6, 2020, Updated March 2, 2020