Delving into multiple ionization of nitromethane using <i>ω</i> /2 <i>ω</i> fs laser fields

We report on the multiple ionization of nitromethane in the near IR region. Based on experiments using linearly and circularly polarized beams, we conclude that the nitromethane dications and trications that ultimately fragment <i>via</i> direct cleavage of the C-N bond are generated by a rescattering process. From the kinetic energies of the ionic fragments and their dependence on the relative phase of the laser fields that constitute an <i>ω</i>/2<i>ω</i> fs asymmetric field, the main dissociation channels have been accurately identified. The existence of at least three nitromethane isomers has been verified by the recorded mass spectra. By the combined study of the deuterated isotopologue, a dissociation channel in the dication that could result in an asymmetric charge distribution is discussed. The characteristics of this channel depend on the laser field intensity. At higher laser intensities, a contribution in the double ionization from HOMO-1 is also detected. This is imprinted by a drastic change in the dependence of the ionic fragments on the phase of the asymmetric field, which highlights the possibilities offered using <i>ω</i>/2<i>ω</i> fs fields.