Molecular dissociation by mid-IR femtosecond pulses

By focusing a MIR femtosecond laser in a cell containing gas-phase metal carbonyls, the resonant infrared multiphoton dissociation of molecules was observed. Cr(CO)6,Mo(CO)6,W(CO)6, and Fe(CO)5 could easily be dissociated, which requires an excitation to at least v=7 or 8 of the CO stretch vibration. After irradiation with ∼150 fs pulses at 5 μm the metal carbonyl practically disappears in favor of free CO, as detected by the IR spectrum. By comparing the power dependence of the total conversion with a model, we can infer that only few vibrational degrees of freedom are involved in the excitation process.