Gas-phase electronic absorption spectra of metallocene dihydrides M(η 5-C 5H 5) 2H 2 (M=Mo, W)

Abstract

The gas-phase electronic absorption spectrum of MoCp 2H 2 (Cp=η 5-C 5H 5) reveals an intense peak at 35 500 cm −1 which is absent in the spectrum measured in n-pentane solution. The spectrum of WCp 2H 2 shows a shoulder at 35 000 cm −1 which disappears on going from the gas to the condensed phase. The term values of these features (16 100 and 16 600 cm −1, respectively) are appropriate for their assignment as the transitions from the HOMO to the lowest Rydberg p-orbitals. The gas-phase spectra of MoCp 2H 2 and WCp 2H 2 give the first examples of clearly defined Rydberg transitions in the organometallic molecules with σ-bonded ligands. Appearance of Rydberg bands confirms that the HOMO of these complexes is really non-bonding.