Barrier top stabilization and temporal control of electrons in an oscillating electric field.

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.

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.

The electronic structure of benzene in the presence of a high-intensity high-frequency circularly polarized laser supports a middle-of-the-ring electron localization. Here, the laser polarization coincides with the ring plane of benzene. The high-frequency oscillating electric field creates circular currents centered at each atom with a circle radius equal to the maximum field amplitude of the laser. All six carbons have six such rings.For a maximum field amplitude of 1.42 Å, which is the carbon-carbon bond distance, all six dynamic current circles intersect to create a deep vortex in the middle, which supports a bound state of a pair of electrons. Such states for benzene can be realized in experiments using a circularly polarized XUV-laser in a range of intensities 10 16 -10 17 W/cm 2 and frequencies 16 eV to 22 eV. Electronic dynamics calculations predict a minimal ionization of benzene when the rise-time of the laser pulse is sudden, indicating a possible experimental realization of these states characterized by a large cut-off in the harmonic generation spectra. This stable electronic structure of the light-dressed benzene is doubly-aromatic due to an extra aromaticity from a D 6h symmetric circular distortion of the σ-framework while the π-electrons, with low density in the ring-plane, are least affected.

The spatio‐temporal localization of a system in the presence of an oscillating electric field for a symmetric double‐well potential is examined via numerical simulations of the time‐dependent Schrödinger equation. For an initial state with equal probability densities in both the wells, stabilized localization atop the barrier can be achieved on a periodic high‐frequency driving. The barrier localization is characterized using Shannon information entropies in position and momentum spaces, defined as Sρ =  −  ∫ |ψ|2 ln |ψ|2 dx and Sγ =  −  ∫ |ϕ|2 ln |ϕ|2 dp, where ψ and ϕ refer to position and momentum space wave functions, respectively. The information entropy sum, Sρ + Sγ, goes through a minimum indicating the formation of the barrier‐localized state, when the peak intensity of the oscillating field is reached. The generalized uncertainty via the Białynicki‐Birula‐Mycielski inequality ( Sρ + Sγ ≥ 1 + lnπ) is saturated upon this minimization. This serves as a signature of the formation of the barrier‐atop localized state, in terms of Shannon entropies of measurable densities.