Concerning the ionization of large polyatomic molecules with intense ultrafast lasers

The relative photoionization/dissociation probabilities are presented for t he molecules benzene, naphthalene, and anthracene upon interaction with 780 nm laser radiation of duration 170 fs and intensity 3.8 X 10(13) W cm(-2). Both the ionization probability and the dissociation yield increase expone ntially from benzene to anthracene as measured by time-of-flight mass spect ra. A structure-based model is presented for the excitation of large polyat omic molecules by intense laser irradiation with pulse widths on the time s cale of molecular vibration (100 fs) and with peak field strengths of 1-2 V Angstrom(-1). The model accounts for molecular structure and is able to ac curately predict the transition from multiphoton ionization (MPI) to tunnel ionization. It is also demonstrated that this structure-based model can qu antitatively predict the experimentally measured ionization probabilities. In comparison, models employing the more conventional zero-range potential do not accurately predict either the transition or the relative ion yield m easured experimentally. (C) 1999 American Institute of Physics. [S0021-9606 (99)01623-2].