Measurements which indicate the existence of a second shortlived state of H²⁻

An apparatus is described in which beams of electrons and H - ions intersect at an angle of 10 degrees . This was used to make a large number of absolute measurements of the detachment cross section of H - for energies between 12 and 22 eV, with an energy resolution of about 0.25 eV. The existence of a large structure in the detachment cross section reported by Walton et al. (1971) was confirmed and, in addition, a second resonance was revealed which had an apparent width of order 0.4 eV at an energy 17.1+or-0.35 eV above the ground state of H - .