Beam transmission experiment reveals an exceptionally large mean bond length in helium dimers, confirming theoretical models of ultra-weak molecular binding.
Key Points
To directly measure the physical size and mean internuclear bond distance of the helium dimer.
Measured relative beam transmissions of helium dimers and atomic helium traversing nanoscale sieves with hole diameters ranging from 98 to 410 nm.
Calculated the mean internuclear distance from relative transmission coefficients across the sieve aperture range.
The mean internuclear distance of the helium dimer was determined to be ⟨r⟩ = 62 ± 10 Å, establishing the largest known molecular bond length.
Corresponded experimental uncertainty to a potential energy well depth of ε/k = 10.88–10.98 K and a binding energy of Eb/k = 0.65–1.30 mK.