Combining certain well-known facts from low-energy scattering theory leads to the accurate determination of the ground-state level ($0^{+}$, $T=1\mathrm{}$) of the ${}_{}{}^2{}_{}{}^{}\mathrm{He}$ nucleus at energy $E=-140-i467\mathrm{}$ keV.

• Received 9 April 1980

DOI:https://doi.org/10.1103/PhysRevLett.45.427