Two-color multiphoton spectroscopy: detection of n = 12-41 Rydberg states in diazabicyclooctane

Two-color multiphoton adsorptions to very high lying (n = 12-41) Rydberg states in diazabicyclooctane and azabicyclooctane are analyzed. The problem of spectral congestion close to the ionization limit is overcome by choosing an appropriate two-photon intermediate electronic state, the lowest-lying 3s Rydberg, to introduce vibrational selectivity in the sequential adsorption process. The subsequent one-photon absorption to the higher lying Rydberg preserves the vibrational selectivity leading to extremely simple, uncongested spectra. The sequential absorptions are monitored by production of ions during subsequent collisions in a low-pressure cell. Analyses of the extended Rydberg series have provided experimental values of ionization potentials to particular vibrationally excited cores to +/-5-cm/sup -1/ resolution. Several series, with differing quantum defects, are seen to converge to each limit. These series are correlated with different symmetry molecular orbitals. Finally, these results suggest that large molecular ions may be produced optically in specific vibrationally excited states by using modifications of this technique.