Laser control over the ultrafast Coulomb explosion of N₂²⁺ after Auger decay: A quantum-dynamics investigation

By theoretical calculation, we demonstrate the possibility to control and partially suppress the Coulomb explosion of N₂ molecules after core-level photoionization by an x-ray laser and subsequent Auger decay. This is achieved by means of a femtosecond infrared laser pulse interacting with the N₂²⁺ dication produced by the x-ray pulse. Suppression of molecular fragmentation requires few-femtosecond IR pulses interacting with the system either during or shortly after the arrival of the x-ray pulse. The IR pulse suppresses fragmentation mostly by optically coupling the electronic routes to ultrafast molecular dissociation with electronic channels able to support long-lived vibrational resonances. The effect is strongly dependent on the orientation of the molecule with respect to the polarization axis of the IR field. Our calculations are motivated by x-ray pump–IR probe experiments performed at an x-ray free-electron laser [J. M. Glownia et al., Opt. Express 18, 17620 (2010)], where only enhancement of N₂²⁺ fragmentation as a function of the pump-probe delay time was reported. The opposite effect reported here becomes apparent when the various electronic channels are considered separately. In practice, this corresponds to a coincident measurement of the energy of the ejected Auger electron