Abstract
This article starts with an introductory survey of previous work on breaking and restoring the electronic structure symmetry of atoms and molecules by means of two laser pulses. Accordingly, the first pulse breaks the symmetry of the system in its ground state with irreducible representation I R R E P g by exciting it to a superposition of the ground state and an excited state with different I R R E P e . The superposition state is non-stationary, representing charge migration with period T in the sub- to few femtosecond time domains. The second pulse stops charge migration and restores symmetry by de-exciting the superposition state back to the ground state. Here, we present a new strategy for symmetry restoration: The second laser pulse excites the superposition state to the excited state, which has the same symmetry as the ground state, but different I R R E P e . The success depends on perfect time delay between the laser pulses, with precision of few attoseconds. The new strategy is demonstrated by quantum dynamics simulation for an oriented model system, benzene.
Highlights
It is nowadays well established that a laser pulse can break the electronic structure symmetry of atoms or molecules, a process that it often followed by charge migration
This part consists of three steps: (i) the symmetry breaking by a circularly right (+) polarized laser pulse and the resulting periodic charge migration; (ii) the design of the laser pulse for symmetry restoration; and (iii) the quantum dynamics simulation of the laser driven symmetry restoration
This paper presents a new strategy for the restoration of the symmetry of electronic structure by means of a well-designed laser pulse, after symmetry was broken by a first laser pulse, which excites the electronic ground state to a superposition of the ground state and an excited state with different
Summary
It is nowadays well established that a laser pulse can break the electronic structure symmetry of atoms or molecules (as in Refs. [1,2,3,4,5,6,7]), a process that it often followed by charge migration (as inRefs. [8,9,10,11,12,13,14,15,16,17,18]). It is nowadays well established that a laser pulse can break the electronic structure symmetry of atoms or molecules We showed that one can employ a well-designed second laser pulse that restores the symmetry of the electronic structure after application of a first symmetry-breaking pulse [19,20,21]. By “symmetry” we mean the molecular point group, e.g., D6h for benzene, or in general the group of all symmetry operations such as rotations, reflections, and inversions that map the initial electronic eigenfunction (or a set of degenerate eigenfunctions) on itself, with the characteristic phase factors that are called “characters”. Symmetry breaking means that the first laser pulse distorts the electronic wave function such that it can no longer be assigned to the original symmetry group. In the case of benzene, the distorted electronic wave function can no
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