Probing Solvation at a Molecular Scale Using Infra-Red Depletion Spectroscopy

Infrared spectroscopy, coupled with mass spectrometry has been used to investigate a specific sized gas phase clusters. In particular, alkali metals i.e. lithium or lanthanides such as ytterbium in the presence of ammonia derivative solvents, has been explored observing both the electronic and vibrational spectral characteristics. Ab initio work has been carried out in support of experimental work which has given some vital clues to help assign some spectra. Firstly, the first electronic spectrum of Li(NH3)4has been observed. Strong absorption is observed in the near-infrared and the band system is assigned to the òT2-X-tilde²A1 transition in the tetrahedral complex. The vibrational structure is indicative of a substantial Jahn-Teller effect in the excited electronic state. Following this, LiNH3 was the next complex to be investigated, the spectra is consistent with two electronic transitions in close proximity, the òE-X-tilde²A1 and B-tilde²A1-X-tilde²A1 systems. Vibrational structure is seen in both systems and the prominence of a particular band is attributed to a Herzberg-Teller coupling. The electronic spectrum of the Li-methylamine cluster was attempted, this spectrum occurrs in the near-infrared and shows provisional bands assigned to the òA-X-tilde²A 0-superscript0-subscript0, B-tilde²A-X-tilde²A 0-superscript0-subscript0 and possibly the C-tilde²A-X-tilde²A 0-superscript0-subscript0 electronic transitions. An effort was made to try and record the IR depletion spectrum of a mixed cluster, such as Li(NH3)n(Ma)m, despite the additional bulk of the methylamine group, up to four solvent molecules were able to reside within the first solvation shell. Finally, the electronic spectrum of the rare earth complex, YbNH3 has been recorded using two colour resonance-enhanced multiphoton ionisation spectroscopy (REMPI). The spectrum arises from a spin-forbidden transition between the ¹A1 ground electronic state and a ³E excited electronic state. Some vibrational structure is also observed in the REMPI spectrum which has been assigned.