Attosecond Charge Migration Can Break Electron Symmetry While Conserving Nuclear Symmetry

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Abstract
Charge migration moves electrons from one molecular site to another, in the typical time domain from few hundred attoseconds to few femtoseconds. On this timescale, the nuclei stand practically still, implying that nuclear point group symmetry is conserved. Since electrons move ultrafast, this can lead to a surprising effect, namely breaking the spatial symmetry of the electron density in spite of the conservation of nuclear framework symmetry. We demonstrate theoretically that attosecond charge migration achieves this electron symmetry breaking if the electrons are prepared in a coherent superposition of non-degenerate electronic ground and excited states which transform according to different irreducible representations. Two simple examples provide a proof-of-principle, namely periodic attosecond charge migration in the σ_g+ σ_u superposition state of the aligned H2+ cation (nuclear point group D_∞h, but electron symmetry breaking D_∞h ---> C_∞v), and in the A_1+B_2 superposition state of the oriented H2O molecule (C_2v versus C_2v ---> C_s).
Funding Information
  • State Administration of Foreign Experts Affairs (D18001)
  • Ministry of Education of the People's Republic of China (D18001, IRT_17R70)
  • Ministry of Science and Technology of the People's Republic of China (2017YFA0304203)
  • National Natural Science Foundation of China (11434007, 11904215, 61378039, 61575115)
  • Fund for Shanxi ?1331 Project? Key Innovation Research Team
  • Talent Program of Shanxi

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