A particle-unstable hydrogen isotope of mass 4 is formed in the reaction ${\pi }^{-}+{\mathrm{Li}}^7\to {\mathrm{H}}^3+{\mathrm{H}}^4$. Two discrete levels of ${\mathrm{H}}^4$ have been found and their binding energies and widths have been determined. Some evidence for the existence of a third level is presented.

• Received 11 March 1968

DOI:https://doi.org/10.1103/PhysRevLett.20.1386