THE ULTRAFAST PHOTODISSOCIATION OF FE(CO)(5) IN THE GAS-PHASE

The photodissociation dynamics of Fe(CO)(5) in a molecular beam have b een investigated with femtosecond time resolution. In single pulse exp eriments, the parent ion Fe(CO)(5)(+) and all the fragment ions Fe(CO) (n)(+), n=0-4 could be observed in linear and reflectron time-of-fligh t (TOF) spectrometers. Ladder switching is suppressed by the use of fe mtosecond laser pulses. The TOF spectra show that the fragmentation pa tterns strongly depend on the laser wavelength, the laser intensity, a nd the laser pulse duration. Femtosecond pump-probe experiments were p erformed for the parent and every fragment molecule. We present a phot odissociation model for the neutral Fe(CO)(5). After the absorption of two 400 nm photons, Fe(CO)(5) looses four CO ligands in about 100 fs. The subsequent dissociation of the fragment Fe(CO) takes place on a l onger time scale of about 230 fs. The measured transient ionization sp ectra of the Fe(CO)(n), n=2-4 fragments represent within the proposed model the fingerprints of the evolution of the [Fe(CO)(5)]double dagge r; transition state on the way to dissociation. We also report on the observation of a metastable ionic fragmentation mechanism. (C) 1998 Am erican Institute of Physics.