Rydberg States of HD

The triplet nf Rydberg states of HD with n=9 -17, L=3, v=1, and R=1,3 have been observed and identified with the laser-molecular beam method. A 20 eV electron beam excites a collimated HD beam to the metastable 2p^3Pi state. Two counterpropagating cw single-frequency laser beams excites the metastable molecule first to the intermediate 3d^3Pi state, then to a triplet nf Rydberg state. The transition frequencies between the 3d and nf states have been measured to an accuracy of 0.02 cm^{-1}. The long range model gives the transition frequencies to an accuracy of approximately 0.1 cm-^{-1}. Using these energy level measurements, the ionization potential of the metastable state has been determined to be 27 460.98(30) cm^{-1} and the energy difference between the triplet metastable and singlet ground state has been determined to be 97 105.50(30) cm ^{-1}. In addition, the linewidths of the triplet Rydberg states have been measured, giving the autoionization rates.