Electronically excited states in size-selected solvated alkali metal atoms. III. Depletion spectroscopy of Na(NH_3)_n-clusters

摘要

The first electronically excited state of small Na(NH_3)_n clusters up to n=22 is studied by means of depletion spectroscopy. A drastic decrease of the excitation energy from the 3s -> 3p transition of the Na atom (16950 cm~(-1) down to 6000 cm~(-1) for the Na(NH_3)_4 cluster, the closing of the first solvation shell, is observed. For larger clusters the excitation energy increases slightly toward the bulk value (6300 cm~(-1)) which represents the absorption of the "solvated" electron. For all Na(NH_3)_n clusters with n>=3 a strong absorption peak is observed near 6600 cm~(-1). By comparison with deuterated sodium-ammonia clusters this absorption can be assigned to an intramolecular vibrational overtone of the ammonia molecule. This indicates a strong coupling between electronical and vibrational excitation in the Na(NH_3)_n clusters.