Communication: Heavy-Rydberg states of HD and the electron affinity of the deuterium atom.

The electron affinity of the deuterium atom has been determined to be 6086.81(27) cm-1 from a measurement of the difference between the D+ + H- and H+ + D- ion-pair dissociation energies and a thermochemical cycle involving the electron affinity of H and the ionization energies of H and D. Heavy-Rydberg states and the ion-pair dissociation thresholds of HD were accessed with good efficiency using a three-photon excitation sequence through the B Σu+1 (v = 22, N = 1) and H¯ Σg+1 (v = 9, N = 0) intermediate levels and the threshold positions were determined using the method of threshold-ion-pair-production spectroscopy.