| Popis: |
Neutral rare gas clusters have one of the simplest kind of chemical binding. Every atom is bound to its neighbours by the same kind of weak undirectional van der Waals force. The first electronic excitation is far in the vacuum UV region [1]. An electron is removed from a strongly antibonding orbital if the duster is ionised. Consequently the bonding becomes much stronger around the charge, and differs in character, direction and strength. The optical absorption shifts to the visible. The absorption is due to the charge localisation on a molecular chromophore. It was originally deduced from energetic considerations and condensed state data [2], that the positive charge in a rare gas cluster ion localizes after about a picosecond on a dimer ion, e.g. Ar 2 + . An argon cluster ion Ar n + would thus have a Ar 2 + Ar n−2. structure. Later experimental [3, 4, 5, 6, 7] and theoretical [8, 9, 10] results pointed to charge localization on a larger unit: Ar n + with n = 3 or 4. This view is not universally shared: Stace and coworkers [11] deduce from their data that the charge does localize on a dimer ion. However Deluca and Johnson [12] and Bowers et al.[13] favour an Ar 2 + − Ar double minimum potential, a notion which is contested by Gadea and Malrieu [14]. Carnovale et al. [15] deduce from their photoelectron spectra n = 3, 7, or 13, depending on cluster size. |
