Resolved high Rydberg spectroscopy of polyatomic molecules and van der Waals clusters.

Using sub-Doppler double resonance excitation with Fourier-transform limited laser pulses and pulsed field ionization techniques we were able to resolve individual high n Rydberg states (45 < n < 110) below and above the lowest ionization energy of van der Waals clusters of benzene with the noble gases neon and argon. By choosing various selected J'K' intermediate rotational states we detected and assigned several Rydberg series with nearly vanishing quantum defect. They converge to different limits representing the rotational states in the vibrational states of the cluster cation.