Nonlinear Time-Dependent Density Functional Theory Studies of Ionization in CO_2 and N_2 by Intense Laser Pulses and Molecular Orbital Reconstruction

摘要

Time-dependent density functional theory, TDDFT, studies of the ionization of CO_2 and N_2, by intense laser pulses peak intensities (3.50xl0~14, 1.40×l0~15, 2.99×l0~15 and 5.59×l0~15 W/cm~2) at 800 nm (ω = 0.0584 a.u.) are presented in the nonlinear nonpertubative regime using the LB94 potential which reproduces the ionization potential of our systems more accurately, without significant increase in computational costs over a local-density approximation. Special emphasis is placed on elucidating molecular orbital (MO) orientation and various peak intensities effects on the ionization processes. The results reveal that molecular orbital ionizations are strongly sensitive to their symmetry (MO shape), the induced dipole coupling between molecular orbitals, and the laser intensities. Notably, we found that with a proper choice of the laser intensity (3.5×l0~14 W/cm~2), the sensitivity is strong enough so that the nature and symmetry of the highest occupied molecular orbital 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 imaging of simple orbitals.