RYDBERG EXCITED IODINE-ARGON VAN-DER-WAALS COMPLEXES STUDIED BY RESONANCE-ENHANCED MULTIPHOTON IONIZATION SPECTROSCOPY

Several new gerade Rydberg states of the I-2-Ar van der Waals complex are reported in the region 53 000-69 000 cm(-1) above the electronic g round state, using mass resolved (2+1) resonance enhanced multiphoton ionization (REMPI) spectroscopy. The spectra all exhibit anharmonic vi brational progressions in the I-2...Ar van der Waals stretching mode, upsilon(3), having typical omega(e), values in the range 49-62 cm(-1), depending upon the principal quantum number of the Rydberg state invo lved. The observed increase in omega(e) and spectral red shift which a ccompanies the increase in principal quantum number is consistent with a progressive strengthening of the van der Waals bond, resulting from less effective shielding of the ion core by the Rydberg electron. The apparent good Franck-Condon overlap in the upsilon(3) mode between th e ground state and the Rydberg states together with the absence of any clear evidence of bending mode progressions in the spectra, indicates that the I-2-Ar complex retains a T-shaped geometry in all the Rydber g excited states observed.