Progress in H{sup {minus}}-spectroscopy

Unlike helium, H{sup {minus}} has no excited states between its ground state and the one-electron continuum beginning in the infrared at 0.7542 eV. Nevertheless, like helium, this simplest of negative ions has a rich structure of doubly-excited, autoionizing states in the vacuum ultraviolet. The author tells about some recent measurements in which several manifolds of states have been addressed using a Doppler-shifted laser beam. In addition, these states have been further probed by imposed electric fields. An interesting pattern is emerging in which the two highly-correlated elections behave as a quasiparticle orbiting the proton. These levels can be described by a modified Rydberg formula in which the quantum defect arises from an internal degree of freedom of the quasiparticle.