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 ground state, using mass resolved (2+1) resonance enhanced multiphoton ionization (REMPI) spectroscopy. The spectra all exhibit anharmonic vibrational 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 involved. The observed increase in omega(e) and spectral red shift which accompanies 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 the 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 Rydberg excited states observed.