Dynamics of Gas-Phase Clusters as Studied by Tune-Resolved Photoelectron

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One of the fundamental issues regarding the properties of clusters, aggregates of atoms or molecules in the gas phase, concerns the dynamics of energy dissipation among their enormous numbers of degrees of freedom. In the present study, we have investigated (1) the energy relaxation processes, (2) the isomerization processes and (3) photodissociation processes of negatively-charged molecular clusters in terms of their geometrical and electronic structures. The findings are summarized as follows :1. The time evolution of the photoelectron signal from an electronically-excited (CィイD26ィエD2FィイD26ィエD2)ィイD2nィエD2ィイD1-ィエD1 is probed by fs time-resolved photoelectron spectroscopy. The excited state is found to decay with a lifetime of 1.5 ps, which can be regarded as the time required for the energy disposal into a specific intermolecular vibrational mode in the cluster anions.2. The electronic structures of (C0ィイD22ィエD2)ィイD2nィエD2ィイD1-ィエD1, (CSィイD22ィエD2)ィイD2nィエD2ィイD1-ィエD1 and [(C0ィイD22ィエD2)ィイD2 … More nィエD2ROH]ィイD1-ィエD1 (R = H, CHィイD23ィエD2) are investigated by photoelectron spectroscopy combined with ab initio calculations, demonstrating the coexistence of isomers having different electronic structures. These "electronic isomers" are well described as [CィイD22ィエD2OィイD24ィエD2ィイD1-ィエD1・ROH(COィイD22ィエD2)ィイD2n-2ィエD2] and [C0ィイD22ィエD2ィイD1-ィエD1・ROH (COィイD22ィエD2)ィイD2n-1ィエD2]3. The photodepletion-photoelectron measurement has revealed the floppiness of the isomeric forms of [(C0ィイD22ィエD2) ィイD24ィエD2HィイD22ィエD2O]ィイD1-ィエD1 clusters : the cluster anions are fluctuating between two forms of isomers as [CィイD22ィエD2OィイD24ィエD2ィイD1-ィエD1・HィイD22ィエD2O (C0ィイD22ィエD2) ィイD22ィエD2] 【double arrow】 [C0ィイD22ィエD2ィイD1-ィエD1・HィイD22ィエD20(C0ィイD22ィエD2) ィイD23ィエD2] at their own temperatures.4. The photodissociation processes of gas-phase tri-iodide anion, IィイD23ィエD2ィイD1-ィエD1, along with its weakly bound clusters, IィイD23ィエD2ィイD1-ィエD1・M, are studied by a combination of an ion-beam technique with a time-of-flight (TOF) method. The experimental results obtained shows convincingly that a single solvent molecule can inhibit the more energy-demanding channel of the IィイD23ィエD2ィイD1-ィエD1 photofragmentation to a considerable extent, which opens up a possibility of controlling the IィイD23ィエD2ィイD1-ィエD1 photofragmentation process via stepwise microsolvation. Less