On the multielectron dissociative ionization of some cyclic aromatic molecules induced by strong laser fields

The interaction of strong laser fields (4 x 10(16) W/cm(2)) with cyclic aromatic molecules (furan, pyrrole, pyridine, and pyrazine) has been studied at lambda = 790 nm. The fragmentation processes of multiply charged transient molecular ions were analyzed by means of a time-of-flight (TOF) spectrometer. Most ion peaks consisted of one broad and one sharp component. From the analysis of the peak profiles the kinetic energies of the molecular and atomic fragment ions have bean measured. On the basis of these energy values and the estimated charge separation distances, it is concluded that, for furan, it is probable that Coulomb explosion takes place in multiple charged parent ions with deformed molecular structure. The doubly charged parent ions of furan and pyrrole fragments through charge separation processes. At higher charged transient parent ions the fragmentation proceeds through direct (instantaneous) process. Moreover, there is evidence that, at least for furan, the ionization process takes place via a direct field ionization mechanism. Pyridine and pyrazine multiple charged ions seem to follow different dissociation routes. The abundance ratios C+/A(+) (A = N, O) for the singly charged atoms were found to be equal to the stoichiometric ratio for all the molecules studied, while a divergence has been observed for the C-2,C-3+/A(2,3+) (A = N, O) ratios.