Preparation and characterization of long-lived molecular Rydberg states: Application to HD

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Abstract
The decay dynamics by predissociation and rotational autoionization of high Rydberg states of HD close to the first few rotational levels of the ground vibronic state of the HD+ cation have been studied by delayed pulsed field ionization following resonant (1+1′) two‐photon absorption via the B state. Although predissociation and autoionization both contribute to the rapid decay of Rydberg states with principal quantum number n≪100, the highest Rydberg states (n≳100) are stable for more than 20 μs. In contrast to H2, channels associated with an HD+ (v+=0, N+=even) ion core are coupled to channels associated with an HD+ (v+=0, N+=odd) ion core. We demonstrate that complex resonances that arise from rotational channel interactions between low (n∼25) Rydberg states characterized by a core with rotational angular momentum quantum number N++2 and the pseudocontinuum of very high Rydberg states characterized by an N+ core can be used with high efficiency to produce long‐lived high Rydberg states. An investigation of the pulsed field ionization characteristics of these complex resonances enables us to measure the branching between diabatic and adiabatic field ionization and to determine the optimal conditions required to extend the method of H‐photofragment Rydberg translational spectroscopy pioneered by Schnieder et al. [J. Chem. Phys. 92, 7027 (1990)] to molecular species.