Nonlinear time-dependent density functional theory studies of the ionization of CO2 by ultrashort intense laser pulses1

Time-dependent density functional theory (TDDFT) studies of the ionization of CO 2 by intense laser pulses (3.50 × 10 14 , 1.40 × 10 15 , 2.99 × 10 15 , and 1.25 × 10 16 W/cm 2 ) at 800 nm ( = 0.0584 au) are presented in the nonlinear nonpertubative regime. Special emphasis is placed on elucidating molecular orbital orientation and various peak-intensities effects on the ionization processes. The results reveal that molecular orbital ionizations are strongly sensitive to their symmetry and the laser intensities. Most notably, we found that with a proper choice of the laser intensity (3.5 × 10 14 W/cm 2 ), the sensitivity is strong enough such that the nature and symmetry of the highest occupied molecular orbital (HOMO) can be directly probed and visualized from the angular dependence of laser-induced ionization. At higher intensities, ionization is found to occur also from inner orbitals, thus complicating the imaging of simple orbitals. A time-dependent electron-localization function (TDELF) is used to get a visual insight on the time evolution process of the electron density.