Electronic spectroscopy of perylene–rare-gas van der Waals complexes

Abstract

Van der Waals (vdW) complexes of perylene (P) with rare-gas atoms R (R=Ne, Ar, Kr, and Xe) were synthesized in seeded supersonic free jet expansions and studied by laser-induced fluorescence spectroscopy. P ⋅ Rn complexes with n=1–4 were identified for all rare gas solvents. The P ⋅ R2 complexes with R=Ar, Kr, and Xe were found to form two spectroscopically distinct species, which are assigned as vdW isomers. The P ⋅ R and P ⋅ R2 intermolecular interactions were calculated using a model calculation based on atom–atom pair potentials, yielding potential energy surfaces, equilibrium structures, and vdW binding energies. The results for P ⋅ R2 support the existence of two different equilibrium structures with almost equal binding energies. The observed microscopic red shifts of P ⋅ R complexes are in excellent agreement with the predictions of microscopic solvent-shift theory based on a second-order perturbative treatment. The microscopic red shifts of the larger P ⋅ Rn complexes can be systematized by additivity rules which reflect their geometric configurations. Intermolecular vibrational excitations in the S1 state were observed for P ⋅ Ar, P ⋅ Kr, P ⋅ Xe, and P ⋅ Xe2 with fundamental frequencies in the range from ν′z =47.2 cm−1 (P ⋅ Ar) to νz =38.7 cm−1 (P ⋅ Xe). The observed frequencies are in excelllent agreement with the values for the out-of-plane modes calculated on the basis of the model intermolecular potentials.