Solvation of ion-pair states in nonpolar media:: I2 in solid neon, argon and krypton

We report on the ion-pair state emission spectra of Iodine isolated in Neon, Argon and Krypton matrices in the spectral range from 300 nm to 700 nm, and present VUV-absorption spectra in the 50 000-60 000 cm(-1) region. Spectroscopic analysis of the UV and visible emission bands of the lowest-lying ion-pair state D-'(2(g)) in Ne and Ar provides unambiguous evidence for both vertical (energy) and horizontal shifts (equilibrium distance) due to solvation in a rare gas matrix, and suggests that the ion-pair states maintain their distinct character. In Krypton the previously reported broad emission band at 420 nm is shown to consist of two narrow bands, which have counterparts in the visible. They are assigned to emission from D-'(2(g)) and a second ion-pair states of I-2, most probably the delta (2(u)) state. Partial charge delocalization to the matrix can only play a minor role in Kr since very similar emission is also found for secondary sites in Ar. These findings should be highly relevant for a description of ion-pair states in nonpolar media. They are also useful for the interpretation of time-resolved experiments that use the ion-pair state emission as probe signal. (C) 2001 American Institute of Physics.