2-COLOR BOUND-FREE-BOUND SPECTROSCOPY OF THE [(2)E(1 2)](C)6S RYDBERGSTATES OF CH3I AND CD3I/

In this resonantly enhanced multiphoton ionization (REMPI) experiment, an extended vibrational progression in the C-I stretching mode (nu(3) ) of methyl iodide (-h(3) and -d(3)) is observed in the 1 + 1' excitat ion of the [1/2] 6s; 0 Rydberg state when the pump photon wavelength l ies in the bound --> free absorption continuum. This is in contrast wi th one-colour coherent (non-resonant) two-photon excitation, where the nu(3) mode is not excited. By working at several different fixed prob e wavelengths and scanning the pump frequency, the relative contributi ons from the three intermediate repulsive states can be explored throu gh changes in the relative strengths of the Omega=0 and 1 components o f the final Rydberg states. Extensive predissociation in the Rydberg s tates curtails the vibrational progression.