Light-dressed states of polyatomic molecules in intense laser fields studied by coincidence momentum measurements

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The three-body Coulomb explosion process of CS_2 in intense laser fields (〜 60 fs, 0.36x10^<15> W/cm^2), CS_2^<3+> → S^+ + C+ + S^+, is studied by the triple coincidence momentum imaging of the atomic fragment ions. The set of the observed momentum vectors of the fragment ions determined for respective explosion events exhibits a dear trajectory originating from the rotational motion of an intermediate CS^<2+> ion, formed in a sequential explosion process of CS_2^<3+> prior to the complete three-body fragmentation. The analysis based on the classical free-rotor model shows that the metastable CS2+ ion has a sufficiently longer lifetime than its rotational period (〜20ps). The molecular structure of CS_2^<3+> just before the Coulomb explosion is reconstructed from the average momentum values of the S^+ and C^+ ions produced through the concerted three-body Coulomb explosion pathways under the assumption that the potential between the fragments is Coulombic. The mean C-S bond length of <r> =2.5A and the azimuthally averaged S-C-S bond angle, <γ> = 145° thus determined indicate that structural deformation occurs to a large extent in the intense laser fields.