Nanosecond multiphoton ionisation of jet-cooled ferrocene

The (Cp)2Fe+ (Cp=η5-C5H5) cations have been obtained in surprisingly high yield by resonance two-colour multiphoton excitation of ferrocene in a jet-cooled molecular beam with tunable nanosecond lasers. The intermediate electronic levels lie in the region of the lowest Rydberg p absorption band. The ion excitation spectrum reveals resolved vibronic structure of the 3dz2→R4px,y transition. The distance between the vibronic components (320 cm−1) corresponds to the metal–ligand stretching frequency in the Rydberg state.