The present study combines both experiment and molecular dynamics simulations in order to document the ionization behavior of the C 6 H 6 -H 2 O and C 6 H 6 -D 2 O complexes close to the ionization threshold, in particular its nonadiabatic character. Using the two-color two-photon resonant ionization laser technique, the ionization thresholds of these species have been measured together with the threshold for dissociative ionization. A binding energy has been deduced for the neutral species: D 0 (C 6 H 6 -H 2 O) ) 106 ( 4 meV and D 0 (C 6 H 6 -D 2 O) ) 116 ( 5 meV, which significantly increases the precision compared to literature. Using a semiempirical potential model, the minimum energy structures of the neutral and ionic species have been determined, and the potential energy surfaces have been analyzed using a two-dimensional approach. As a result, the formation of a stable C 6 H 6 + -H 2 O complex close to the threshold is found to be controlled by a pure quantum effect and is ascribed to the classically forbidden region of the neutral ground state wave function for the intermolecular vibrational motion. Using classical molecular dynamics simulations in order to sample this region, it has been shown that the neutral conformations involved in the production of stable ions at the ionization threshold exhibit a strong geometry change compared to the neutral equilibrium conformation; i.e., the water molecule is strongly shifted off the benzene C 6 axis and is also flipped over backward the benzene ring. The difference in the ionization energy of the C 6 H 6 -H 2 O and C 6 H 6 -D 2 O complexes, which cannot be explained by the difference in the neutral binding energies alone, supports this result.

This work presents a quantitative comparison between experiment and molecular dynamics simulations for the excitation spectra of large van der Waals clusters. The emission and excitation spectra of mixed Ba(Ar)n clusters have been obtained for average cluster sizes ranging between 300 and 4000. The simulation is performed by using classical dynamics and pairwise additive potentials for two cases corresponding to the barium atom at the surface or inside the argon cluster. A very good agreement with the experiment is found when the barium atom is at the surface.

The absorption spectra of thin film samples, formed by the codeposition of sodium vapor with the rare gases have long been known to consist of complex structures in the region of the atomic sodium "yellow-doublet" lines. The photophysical characteristics of the associated luminescence (excitation/emission) spectra, indicate strong interaction between the excited P state Na atom and the rare gases (Ar, Kr, and Xe) used as host solids. This system is reinvestigated with new experimental spectroscopic results and molecular dynamics (MD) calculations. The so-called "violet" site in Ar and Kr has been produced by laser excitation of thermally deposited samples. The simulation of the "spray-on" deposition of thin films enables identification of tetravacancy (tv) sites of isolation for ground-state atomic sodium in Ar while in Kr this site is found in addition to single vacancy (sv) occupancy. Various cubic symmetry sites were taken into account to simulate absorption and emission spectra using accurate interaction potentials for the Na · RG diatomics. The wellknown 3-fold splitting in absorption, attributed to the Jahn-Teller effect, was very well reproduced but the simulated spectra for all the sites considered are located in the low energy region of the experimental bands. The evolution of the excited state Na atom is followed revealing the nature and symmetry of the sites that are transiently occupied. Consistent with the large Stokes shift observed experimentally, there is an extensive rearrangement of the lattice in the excited state with respect to the ground state. Combining all the experimental and theoretical information, an assignment of experimental violet, blue, and red absorption features is established involving single vacancy, tetravacancy, and hexavacancy sites, respectively, in Ar and Kr.