A study of ionisation of free and clustered molecules under the action of femtosecond laser radiation

We have investigated the processes of excitation and ionisation of monomers and clusters of CF₃I, IF₂CCOF and Fe(CO)₅ molecules under the action of femtosecond laser radiation at the wavelengths of 266, 400 and 800 nm. It is concluded that the nature of the excitation of free molecules and clustered molecules by femtosecond pulses is different. The simulation of the ionisation yield of the objects under study has shown that the multiphoton ionisation is the key mechanism in the case of free molecules, while the field ionisation may play a significant role for clusters, in particular, in the case of ionisation at the wavelength of λ = 800 nm.