Multiple-orbital effects in laser-induced electron diffraction of aligned molecules

Abstract

Photoelectron Angular Distributions (PADs) resulting from 800 nm and 1300 nm strong field ionization of impulsively aligned CF3I molecules were analyzed using time-dependent density functional theory (TDDFT). The normalized difference between the PADs for aligned and anti-aligned molecules displays large modulations in the high-energy re-collision plateau that are assigned to the diffraction of back-scattered photoelectrons. The TDDFT calculations reveal that, in spite of their 2.6 eV energy difference, ionization from the HOMO-1 orbital contributes to the diffraction pattern on the same footing as ionization from the doubly degenerate HOMO orbital.Following structural changes within single molecules on their natural time and length scales is one of the great challenges in ultrafast molecular physics. Large efforts are currently devoted to the development of techniques for the direct imaging of nuclear motion with atomic resolution. Diffractive imaging methods using ultrashort X-ray pulses available at Free Electron Lasers [1, 2], or using ultrashort electron pulses [3][4][5], have the potential to record structural information with the spatiotemporal resolution required for obtaining "molecular movies" [3,[5][6][7]. In both approaches however, realizing single molecule imaging with sub-10 fs temporal resolution has proven challenging [8,9], since the required synchronization between the visible/ultra-violet laser pulses initiating the molecular dynamics of interest and the Xray/UED probe is difficult to achieve.Fully laser-based molecular self-imaging techniques using strong field ionization by an intense infrared (IR) laser pulse are an alternative and promising route towards the imaging of (time-dependent) molecular structures in the gas phase [10]. In particular, Laser-Induced Electron Diffraction (LIED) [11][12][13][14], where the ionization of a molecule by a strong IR laser field leads to the creation of a photoelectron wavepacket that is accelerated by the laser field to induce a recollision with the parent molecular ion, has already demonstrated fewfemtosecond and sub-Ångström resolution [15][16][17]. The time resolution in LIED is given by the optical cycle of the driving laser field [15,17] and can reach the subfemtosecond timescale, whereas high spatial resolution is possible due to the high kinetic energy of the re-colliding photoelectron, which determines its De Broglie wavelength and can reach values of 0.1Å when using midinfrared laser fields.Retrieval of the molecular structure from an LIED experiment is often done in the framework of the Quan-titative Rescattering Theory (QRT) [13,18,19], which usually assumes that (i) the ionization takes place from the Highest Occupied Molecular Orbital (HOMO) and that (ii) the initial shape of the electron wavepacket is lost during its propagation in the oscillatory laser field, so that the re-colliding electron wavepacket can be approximated by a plane wave. Both of these assumptions may be questioned. Strong field ionization, in particular of polyatomic mol...

Local Berry curvature signatures in dichroic angle-resolved photoelectron spectroscopy from two-dimensional materials

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Atomic-resolution imaging of carbonyl sulfide by laser-induced electron diffraction

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Ultrafast Hole Deformation Revealed by Molecular Attosecond Interferometry

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