Spectroscopy of small molecules and clusters

• Main Author: Ayles, Victoria Louise
• Published: University of Nottingham 2008
• Subjects: 541.22; QD450 Physical and theoretical chemistry
• Online Access: http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.495565

The 3s, 3d and 4s Rydberg states of nitric oxide (NO), bound to a rare gas (Rg) atom in a van der Waals complex (NO-Rg), are probed using resonance-enhanced multiphoton ionisation, in order to investigate the effect of electronic excitation on these complexes. The spectroscopy is interpreted in terms of interactions between the Rydberg electron, the nitric oxide (NO+) core and the Rg atoms. Larger NO-Rgx clusters are investigated offering the prospect of bridging the spectroscopic gap between van der Waals dimers and the bulk. The spectroscopy is determined by an NO+-Rg2 moiety and formation of the Rydberg state provokes a dynamic response from the Rgx cluster, similar to that observed in matrix studies. High-resolution zero electron kinetic energy spectroscopy is employed to derive vibrational frequencies of the para-fluorotoluene cation and assignments for previously unidentified (or in some cases, erroneously assigned) features have been presented. The first electronically-excited state of para-fluorotoluene (pFT), where a pFT chromophore is bound to several pFT molecules in a van der Waals cluster, has been studied. The effects of laser power and the internal temperature of the clusters on the fragmentation are considered. A model potential analysis is carried out to determine whether binding in metal cation/rare gas (M+-Rg) complexes is physical (due to electrostatic, dispersion and induction interactions), or whether a chemical component (classical covalent interactions) must be considered. For alkali metal (Alk+)/Rg complexes, the model potential successfully describes the binding (the interaction is purely physical). For Au+-Rg, the model potential analysis reveals the emergence of a chemical component to the interaction, which becomes more significant as Rg gets larger.