RESUMEN
The dynamics of two electrons in a three-dimensional symmetric double-well quantum system is controlled using a high frequency oscillating electric field, achieving pairing of electrons and barrier-top localization. The field parameters of oscillating electric field intensity and frequency which are required to induce such an effect of barrier-top stabilization are easily estimated using time-independent Kramers-Henneberger electronic structure Full Configuration Interaction (FCI) calculations in an oscillating frame of reference with a Gaussian basis set. In the presence of the laser, the energy of the two-electron system in the symmetric double-well is found to be minimized when the barrier-top dynamic stabilization happens. Furthermore, the barrier-stabilized state finds importance in achieving a temporal control over electronic ionization. From approximate time-dependent calculations in the laboratory frame, the signatures of the barrier stabilized state are realized and it is observed that the paired-up state remains stable as long as the continuous wave region of the laser pulse is on. Ionization happens as soon as the laser pulse is switched off, because of the increased electronic repulsion in the paired up barrier-top state, thus giving a temporal control over laser-induced ionization.
RESUMEN
The (t, t') method for quantum dynamics with general time-dependent Hamiltonians is exact yet expensive to implement, in the context of laser-atom, laser-molecule interactions. The evolution operator requires a huge storage space with a large operation count for the propagation. A new method is suggested in this work where an analytical block diagonalization of the Floquet Hamiltonian is proposed. The block diagonalization in this novel algorithm is based on Chebyshev polynomials of the second kind. This is combined with a split operator method of chosen order to approximate the full evolution operator. The number of operations are drastically reduced to that of a matrix-vector multiplication repeated only to the order of the number of Floquet channels. Hence, only matrices of the order of the number of position basis functions need to be stored. Thus, the presented algorithm is an effective tool for solving the (t, t', t'') problem for interactions with a bichromatic laser and a single-frequency laser pulse with explicit interactions of the pulse envelope. Hydrogen atom, helium, water, and ammonia, represented with Hamiltonians obtained from standard electronic structure packages, have been investigated in the presence of linearly polarized pulsed laser fields and bichromatic laser fields presenting various time-dependent properties from the program.
RESUMEN
A high-intensity, high-frequency laser can create an oscillating induced dipole moment in a molecule. At high laser frequencies with a long pulse width, a stable non-ionizing state with a laser-induced hybridization of the electrons is formed. For ammonia, aligned with the linear polarization direction of the laser, such stable states can be realized. Electronic hybridization in the presence of the high-frequency field is such that the lone pair propensity is dynamically equalized on either side of ammonia. This leads to a destabilization of pyramidal ammonia and hovering states with the electron density flipping to either side of the geometry. Electronic structure calculations in an oscillating frame of reference anticipate this effect with a predicted classical quiver distance of 0.1 Å. Electronic dynamics at a laser intensity of 1.14 × 1013 W/cm2 and a frequency of 8.16 eV predicts negligible ionization for the planar geometry. Approximate nuclear wave packet dynamics in the oscillating potential energy generated by the electrons predicts a trapping of ammonia in its planar transition state geometry.