Surface-melting transitions and phase coexistence in argon solvent clusters

Electronic spectra of carbazole{·}Arₙ clusters in supersonic beams exhibit specific size-dependent spectral features, showing only sharp intermolecular vibrational bands for n=1 to 3, both broad and narrow spectral bands for n=4 to 6, and only broad bands for n{≥}7. Monte Carlo simulations indicate that the change from sharp to broad structure is due to surface melting transitions of the solvent clusters relative to the substrate, and predict a finite-width solidlike-liquidlike coexistence range in agreement with the experimental observations.