RYDBERG TRANSITIONS ORIGINATING AT METAL-LOCALIZED ORBITALS IN LARGE POLYATOMIC MOLECULES: A GAS-PHASE SPECTROSCOPIC STUDY OF TRANSITION- METAL SANDWICH COMPLEXES
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Date
1996
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Ohio State University
Abstract
The transition-metal sandwich compounds with an occupied totally symmetric valence molecular orbital (MO) derived from the metal $d_{z}(2)$ appear to represent the first example of polyatomic molecules revealing in the photoabsorption spectra well-resolved Rydberg transitions from a metal-localized MO. The gas-phase UV absorption spectra of ($\eta^{6}$-Arene)$_{2}M$ (M = V, Cr, Mo, W), ($\eta^{5}-C_{5}H_{5})_{2}M$ (M = V, Fe, Ru, Os), ($\eta^{6}$-Arene)($\eta^{5}-C_{5}H_{5}$)Mn, ($\eta^{7}-C_{7}H_{7}$)M (M = V, Nb, Cr, Mo, W) show sharp bands arising from the transitions originating at the metal $d_{z}{2}$ orbital and terminating at Rydberg ns, np and nd levels. Due to the low $d_{z}{2}$ ionisation energies, even higher Rydberg excitations in this compounds lie as a rule, below $50000 cm^{-1}$ making it easy to investigate them using standard UV-visible spectrometers. Rydbberg features disappear on going to the condenced media resulting in a dramatic difference between the gas phase and solution-phase spectra of sandwich complexes. All Rydberg bands observed have been assigned on the basis of corresponding term values and effective quantum numbers. These parameters appear to change very little on going from one sandwich to another. For bisarene and mixed sandwiches, many-membered Rydberg np series converging on the $d_{z}{2}$ ionization limit have been revealed and the corresponding ionization potentials have been calculated with high accuracy using the Rydberg formula. Clear examples of molecular symmetry influence on the Rydberg structure, Rydberg/valence mixing and vibronic coupling in Rydberg states will be presented.
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Author Institution: G.A. Razuvaev Institute of Organometallic Chemistry, Russian Academy of Sciences