Microscopic solvation. The first solvent shell

Abstract

Optical spectra of carbazole · Ar_n clusters (n= 1–36) produced in supersonic beams have been measured by size-selective resonant two-photon ionization (R2PI) techniques. Spectral features such as band shifts, widths and shapes are highly specific and size-dependent, and many discontinuous changes occur as a function of size. Structures, dynamics, and order–disorder transitions of these rare-gas solvent clusters were studied by molecular dynamics (MD) and Monte-Carlo (MC) simulations. Seven different order–disorder transitions were found. The simulations indicate that the changeover from narrow to broad spectral structures for n= 4–6 is due to quasi-two-dimensional surface-decoupling transitions. For clusters with n= 8–20, spectral shifts, bandwidths and bandshapes are influenced by three-dimensional order–disorder transitions (wetting–non-wetting, second-layer promotion and side-crossing transitions). Closure of the first solvent shell takes place at n≈ 30.