Attosecond Nuclear Dynamics in the Ammonia Cation: Relation between High‐Harmonic and Photoelectron Spectroscopies

Kraus, Peter M.; Wörner, Hans Jakob

doi:10.1002/cphc.201201022

Cited by 36 publications

(48 citation statements)

References 29 publications

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“…more than 73 % of the molecules pointing in the same direction, under completely field-free conditions. Details of the experimental setup have been given elsewhere [26,34]. The degrees of orientation obtained in this study rival those obtained after quantum-state selection [23] with a ∼10 6 -fold increase in particle density.…”

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confidence: 63%

Two-Pulse Field-Free Orientation Reveals Anisotropy of Molecular Shape Resonance

2014

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We report the observation of macroscopic field-free orientation, i.e. more than 73 % of CO molecules pointing in the same direction. This is achieved through an all-optical scheme operating at high particle densities (> 10 17 cm −3 ) that combines a one-color (ω) and a two-color (ω + 2ω) non-resonant femtosecond laser pulses. We show that the achieved orientation solely relies on the hyperpolarizability interaction as opposed to an ionization-depletion mechanism thus opening a wide range of applications. The achieved strong orientation enables us to reveal the molecularframe anisotropies of the photorecombination amplitudes and phases caused by a shape resonance. The resonance appears as a local maximum in the even-harmonic emission around 28 eV. In contrast, the odd-harmonic emission is suppressed in this spectral region through the combined effects of an asymmetric photorecombination phase and a sub-cycle Stark effect, generic for polar molecules, that we experimentally identify.Techniques for fixing molecules in space are invaluable tools for a broad range of experiments in ultrafast science [1,2]. The availability of transiently aligned molecular samples has particularly advanced strong-field and attosecond spectroscopies, providing new insights into the electronic structure of molecules and its temporal evolution [3][4][5][6][7]. High-harmonic spectroscopy (HHS) provides a new access to the rich structures of photoionization continua, such as Cooper minima [8][9][10][11] and shape resonances [11][12][13]. The investigation of the inherent structural and dynamical anisotropies of polar molecules has however been prevented by the difficulty of orienting molecules. Interesting phenomena tied to polar molecules include the predicted recombination-site dependence of structural minima [14,15] and attosecond charge migration [16][17][18] triggered by strong-field ionization. Here, we demonstrate a protocol for molecular orientation which achieves macroscopic field-free orientation and exploit this progress to probe the anisotropy of photorecombination dipole moments at a molecular shape resonance.Successful approaches to laser-induced molecular orientation include the combination of an electrostatic field with a rapidly turned-off laser field [19], alignment in combination with quantum-state selection and a weak dc-field [20][21][22][23], adiabatic [24] and impulsive two-color orientation [25][26][27]. All of these techniques are subject to substantial limitations: The presence of electric fields may alter the electronic structure of the molecule, its photo-induced dynamics or the subsequent probing process. The low particle densities available after quantumstate selection make the application of such techniques to high-harmonic and attosecond spectroscopies challenging to impossible. The two-color scheme [22,25], recently applied to HHS [26,27], relies on an ionization-depletion mechanism [28] and thus ties the achievable degree of orientation to the ionization fraction of the sample. This fact does not only limi...

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supporting

confidence: 63%

Two-Pulse Field-Free Orientation Reveals Anisotropy of Molecular Shape Resonance

2014

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“…Nuclear motion of HCCI + following strong-field ionization was included through the approach outline in Ref. 105, i.e., through nuclear auto-correlation functions 46,106 derived from experimental photoelectron spectra 107 . Finally, since the molecules were not perfectly aligned, the variation of the strong-field-ionization rate with the alignment angle was also required.…”

Section: Charge Migrationmentioning

confidence: 99%

Charge migration and charge transfer in molecular systems

Wörner

Arrell

Banerji

et al. 2017

Structural Dynamics

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The transfer of charge at the molecular level plays a fundamental role in many areas of chemistry, physics, biology and materials science. Today, more than 60 years after the seminal work of R. A. Marcus, charge transfer is still a very active field of research. An important recent impetus comes from the ability to resolve ever faster temporal events, down to the attosecond time scale. Such a high temporal resolution now offers the possibility to unravel the most elementary quantum dynamics of both electrons and nuclei that participate in the complex process of charge transfer. This review covers recent research that addresses the following questions. Can we reconstruct the migration of charge across a molecule on the atomic length and electronic time scales? Can we use strong laser fields to control charge migration? Can we temporally resolve and understand intramolecular charge transfer in dissociative ionization of small molecules, in transition-metal complexes and in conjugated polymers? Can we tailor molecular systems towards specific charge-transfer processes? What are the time scales of the elementary steps of charge transfer in liquids and nanoparticles? Important new insights into each of these topics, obtained from state-of-the-art ultrafast spectroscopy and/or theoretical methods, are summarized in this review.

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“…This orientation has been already experimentally realized and variation of the orientation did not reveal contributions to the ionization from lower lying orbitals [5]. The TDSE ionization yields are compared to the ones obtained using Ammosov-Delone-Krainov (ADK) tunneling rates Γ ADK [14,15] and the recently introduced frequency-corrected ADK (FC-ADK) model [18] based on the Perelomov-Popov-Terent'ev (PPT) [13] theory.…”

Section: Methodsmentioning

confidence: 99%

“…It was shown that the required nuclear autocorrelation functions can be obtained from photoelectron spectra [4][5][6]. The photoelectron spectra revealed that the inversion (or umbrella) mode is the only vibrational mode in which a significant nuclear motion is triggered by the laser field [5]. Importantly, it was shown that the strong geometrydependence of the ionization rate, the key ingredient for Lochfraß, must indeed be considered in order to quantitatively match the experimental PACER results [5,6].…”

Section: Introductionmentioning

confidence: 99%

“…Recently, the relative nuclear motion launched in the cations NH was studied and experimentally observed by comparison of the respective high-harmonic spectra [5,6] using the so-called PACER (Probing Attosecond dynamics with Chirp-Encoded Recollisions) technique [2,3]. It was shown that the required nuclear autocorrelation functions can be obtained from photoelectron spectra [4][5][6]. The photoelectron spectra revealed that the inversion (or umbrella) mode is the only vibrational mode in which a significant nuclear motion is triggered by the laser field [5].…”

Section: Introductionmentioning

confidence: 99%

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Imaging of the umbrella motion and tunneling in ammonia molecules by strong-field ionization

et al. 2016

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The geometry-dependent ionization behavior of the ammonia molecule is investigated. Different theoretical approaches for obtaining the ionization yield are compared, all of them showing a strong dependence of the ionization yield on the inversion coordinate at long wavelengths (≥ 800 nm). It is shown how this effect can be exploited to create and probe nuclear wave packets in neutral ammonia using Lochfraß. Furthermore, imaging of a wave packet tunneling through the barrier of a double-well potential in real time is discussed.

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Attosecond Nuclear Dynamics in the Ammonia Cation: Relation between High‐Harmonic and Photoelectron Spectroscopies

Cited by 36 publications

References 29 publications

Two-Pulse Field-Free Orientation Reveals Anisotropy of Molecular Shape Resonance

Two-Pulse Field-Free Orientation Reveals Anisotropy of Molecular Shape Resonance

Charge migration and charge transfer in molecular systems

Imaging of the umbrella motion and tunneling in ammonia molecules by strong-field ionization

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