Isotope Effect in Tunneling Ionization of Neutral Hydrogen Molecules

Wang, X.; Xu, Han; Atia-Tul-Noor, A.; Hu, Bitao; Kielpinski, David; Sang, R. T.; Litvinyuk, Igor

doi:10.1103/physrevlett.117.083003

Cited by 17 publications

(8 citation statements)

References 27 publications

(25 reference statements)

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“…Since τ rot ∝ √ M , the dynamical rotation is influenced by the specific isotope. Indeed, recently the isotope effect in tunneling ionization of molecules has attracted considerable attention [52,53]. We finally investigate whether an isotope effect can be observed in the ion angular distributions of HeH + and HeD + .…”

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confidence: 96%

Strong-field polarizability-enhanced dissociative ionization

et al. 2018

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We investigate dissociative single and double ionization of HeH + induced by intense femtosecond laser pulses. By employing a semi-classical model with nuclear trajectories moving on field-dressed surfaces and ionization events treated as stochastical jumps, we identify a strong-field mechanism wherein the molecules dynamically align along the laser polarization axis and stretch towards a critical internuclear distance before getting dissociative ionized. As the tunnel-ionization rate is greater for larger internuclear distance and for aligned samples, ionization is enhanced. The strong dynamical rotation is traced back to a maximum in the parallel component of the internucleardistance-dependent polarizability tensor. Qualitative agreement with our experimental observations is found. Finally the criteria for observing the isotope effect for the ion angular distribution is discussed.PACS numbers: 33.80. Wz, 33.80.Eh, 42.50.Hz The ionization and dissociation of small molecules in intense laser fields is of fundamental interest and has captured the attention of physicists for many years [1][2][3]. When the ratio of the laser frequency to the peak electric field is sufficiently small, the ionization process can be considered as an electron tunneling through the instantaneous barrier formed by the field and the Coulomb potential of the system [4]. In molecules, such tunnelionization rates depend on the spatial separation between the nuclei [5-9], as well as the molecular orientation with respect to the laser polarization axis, where the ionization rate follows the shape of the highest-occupied molecular orbital [10][11][12]. In addition to these fixed-nuclei properties, the molecules will dynamically rotate and stretch in the field, potentially leading to fragmentation [8]. Here, we theoretically identify a new fragmentation pathway that involves the combination of the aforementioned strong-field dynamics. Namely, due to the force resulting from the internuclear-distance-dependent polarizability tensor, the molecule is simultaneously aligned and stretched towards a specific internuclear distance in the field-dressed ground state before being ionized. We denote it as polarizability-enhanced dissociative ionization (PEDI) and support our findings with experimental data.Polarizability effects have been explored extensively in strong-field physics, e.g. it has regularly appeared in the interpretation of strong-field ionization experiments [13,14], and the anisotropic polarizability is often exploited in molecular alignment experiments [15][16][17]. In dissociative ionization studies involving short laser pulses (tens of femtoseconds (fs) duration), often only the vibrational degrees of freedom are considered, while the rotational dynamics are disregarded. This is based on the intuition that the field-free rotational timescale of picoseconds is much greater than the vibrational timescale of fs and thus rotational motion can be safely neglected.However, as several works employing semiclassical methods [7,18,19] have show...

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confidence: 96%

Strong-field polarizability-enhanced dissociative ionization

et al. 2018

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“…Such high energy photon can release electrons directly into the continuum to suppress additional excitation effects. The single circularly polarized probe pulse with equal field amplitudes in each orthogonal direction does not influence the symmetry of photoionization . Such ultrafast attosecond X-ray pulses have been generated by current laser techniques from circularly polarized high harmonics. , We vary the CEP ϕ of the pump pulse while the CEP of the probe pulse E pr ( t ) is always fixed at zero.…”

Section: Resultsmentioning

confidence: 99%

Ultrafast X-ray Photoelectron Imaging of Attosecond Electron Dynamics in Molecular Coherent Excitation

Yuan

Bandrauk

2019

J. Phys. Chem. A

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Ultrafast photoelectron imaging allows to measure information about coherent electron dynamic processes in materials or chemical compounds on femtosecond to attosecond time scales. We show that molecular time-resolved photoelectron diffraction produced by a time-delayed soft X-ray attosecond pulse can be used to monitor the ultrafast coherent excitation induced by a resonant UV pump pulse with variable carrierenvelope phases. Asymmetric diffraction angular patterns illustrate coherent electron dynamics of charge migration with spatiotemporal resolution on the attosecond and ångstrom scale. This allows the temporal reconstruction of phases and amplitudes of electronic states and geometry of molecules as a function of time delay of the probe pulse and carrier-envelope phases of the pump pulse. Results are obtained from solutions of time-dependent Schrodinger equations of the hydrogen molecular ion, and analyzed by ultrafast photoelectron diffraction models for coherent superposition of electronic states. The present demonstration provides a guiding principle for monitoring ultrafast spatiotemporal coherent electron dynamics and imaging molecular electronic structure in complex systems by ultrafast pump−probe experiments and their dependence on carrier-envelope phases and time delays.

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“…However, due to the nuclear mass difference, the evolution of nuclear wave packet while electron propagates in the continuum and then recombines to the ground state may differ substantially. The harmonic intensity from the heavy isotope was shown to be higher compared to the lighter molecule as harmonic emission is sensitive to the nuclear motion [6] though for D 2 the ionization probability is less than for H 2 [22]. The aim of this work is to measure a small phase difference of HHG signals and to gain an insight into the correlated electron-nuclear dynamics for the two isotopes of molecular hydrogen.…”

Section: Gouy Phase Interferometermentioning

confidence: 99%

Attosecond delays of high harmonic emissions from isotopes of molecular hydrogen measured by Gouy phase XUV interferometer

Mustary¹,

Li²,

Wu³

et al. 2021

Preprint

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High harmonic spectroscopy [1][2][3] can access structural and dynamical information on molecular systems encoded in amplitude and phase of high harmonic generation (HHG) signals [4][5][6][7][8][9]. However, measurement of the harmonic phase is a daunting task. Here we present a precise measurement of HHG phase difference between two isotopes of molecular hydrogen using the advanced extreme-ultraviolet (XUV) Gouy phase interferometer [10]. The measured phase difference is about 200 mrad, corresponding to ∼ 3 attoseconds

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Isotope Effect in Tunneling Ionization of Neutral Hydrogen Molecules

Cited by 17 publications

References 27 publications

Strong-field polarizability-enhanced dissociative ionization

Strong-field polarizability-enhanced dissociative ionization

Ultrafast X-ray Photoelectron Imaging of Attosecond Electron Dynamics in Molecular Coherent Excitation

Attosecond delays of high harmonic emissions from isotopes of molecular hydrogen measured by Gouy phase XUV interferometer

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