PREPARATION AND CHARACTERIZATION OF LONG-LIVED MOLECULAR RYDBERG STATES - APPLICATION TO HD

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 th HD+ cation have been studied by delay ed pulsed field ionization following resonant (1+1') two-photon absorp tion via the B state. Although predissociation and autoionization both contribute to the rapid decay of Rydberg states with principal quantu m number n much less than 100, the highest Rydberg states (n>100) are stable for more than 20 mu s. In contrast to H-2, channels associated with an HD+ (upsilon=0,N+=even) ion core are coupled to channels assoc iated with HD+ (upsilon(+)=0,N+=odd) ion core. We demonstrate that com plex resonances that arise from rotational channel interactions betwee n low (n similar to 25) Rydberg states characterized by a core with ro tational angular momentum quantum number N++2 and the pseudocontinuum of very high Rydberg states characterized by an N+ core can be used wi th high efficiency to produce long-lived high Rydberg states. An inves tigation of the pulsed field ionization characteristics of these compl ex resonances enables us to measure the branching between diabatic and adiabatic field ionization and to determine the optimal conditions re quired to extend the method of H-photofragment Rydberg translational s pectroscopy pioneered by Schnieder et al.[J. Chem. Phys. 92, 7027 (199 0)] to molecular species. (C) American Institute of Physics.