Molecular ionization of cyclohexanone in femtosecond laser fields: An application of ADK theory

The mechanisms of ionization and dissociation of cyclohexanone (C ₆H₁₀O) in a 90 fs, 788 nm linearly polarized laser field ranging from 10¹³ to 10¹⁴ W/cm² by a time-of-flight mass spectrometer (TOF-MS) have been investigated. The ion yields as a function of laser intensity have been measured experimentally. By comparison with the Ammosov-Delone-Krainov (ADK) theory based on a hydrogen-like model, the ionization mechanism of cyclohexanone in this intense femtosecond laser field has been understood. Considering the importance of molecular nuclear motions, we propose that the Franck-Condon (F-C) factor can provide the excess vibrational energy in the molecular ion. This energy is required for the decomposition of the molecular ion which finally results in the observed mass spectrum.