Journal of Physical Chemistry A, Vol.101, No.6, 1081-1092, 1997
Wavelength-Dependent Photodissociation of (Fe(bpy)(3)Center-Dot(CH3OH)(N))(2+) Clusters, N=2-6, Triggered by Excitation of the Metal-to-Ligand Charge-Transfer Transition
This paper reports the first investigation of the energetics of charge transfer in a coordination complex containing a divalent transition-metal ion as a function of the extent of solvation and provides a detailed description of the first instrument designed for spectroscopic characterization of gas-phase ions and clusters produced by electrospray ionization. Metal-to-ligand charge transfer (MLCT) is probed by laser photofragmentation mass spectrometry in clusters of the complex tris (2,2’-bipyridyl)iron(II), [Fe(bpy)(3)](2+), with methanol prepared by electrospray ionization. Excitation of the MLCT transition in [Fe(bpy)(3)](2+) triggers evaporation of methanol solvent molecules from these clusters, permitting indirect detection of absorption. Measurement of ion beam depletion and/or production of charged photofragments as a function of photon energy yields the red edge of the MLCT band for [Fe(bpy)(3) (CH3OH)(n)](2+) clusters, n = 2-6. Increasing the number of methanol molecules in the clusters shifts the onset of the MLCT band to lower energies, reflecting preferential solvation of the MLCT excited state of [Fe(bpy)(3)](2+) relative to its ground state. A measurable fraction of mass-selected [Fe(bpy)(3)(CH3OH)(n)](2+) clusters also lose methanol molecules through metastable decomposition between primary mass selection and secondary mass analysis. Application of the evaporative ensemble model with RRK rate constants for metastable decomposition permits estimation of sequential methanol binding energies and internal temperatures for [Fe(bpy)(3)(CH3OH)(n)](2+) clusters prepared by electrospray ionization.
Keywords:ION-MOLECULE REACTIONS;THERMODYNAMICALLY STABLE DICATIONS;IONIZATION MASS-SPECTROMETRY;GAS-PHASE;ELECTROSPRAY-IONIZATION;VIBRATIONAL STRUCTURE;BINDING-ENERGIES;DECAY FRACTIONS;MAGIC NUMBERS;SMALL ALKANES