Communication: The ionization and dissociation energies of HD.

The adiabatic ionization energy [in units of hc, E(i)=124 568.485 81(36) cm(-1)] and the dissociation energy [D(0)=36 405.783 66(36) cm(-1)] of HD have been determined using a hybrid experimental-theoretical method. Experimentally, the wave numbers of the EF(v=0,N=0)→np[X(+)(v(+)=0 and 1, N(+)=0)] and EF(v=0,N=1)→np[X(+)(v(+)=0,N(+)=1)] transitions to singlet Rydberg states were measured by laser spectroscopy and used to validate predictions of the electron binding energies by multichannel quantum defect theory. Adding the transition energies, the electron binding energies and previously reported term energies of the EF state led to a determination of the adiabatic ionization energy of HD and of rovibrational energy spacings in HD(+). Combining these measurements with highly accurate theoretical values of the ionization energies of the one-electron systems H, D, and HD(+) further enabled a new determination of the dissociation energy of HD.