Dynamics of N<sub>2</sub> Dissociation upon Inner-Valence Ionization by Wavelength-Selected XUV Pulses

Eckstein, Martin; Yang, Chung-Hsin; Kubin, Markus; Frassetto, Fabio; Poletto, Luca; Ritze, H.‐H.; Vrakking, Marc J. J.; Kornilov, Oleg

doi:10.1021/jz5025542

Cited by 57 publications

(68 citation statements)

References 28 publications

(59 reference statements)

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“…2(a)], the theoretical kinetic energy spectrum exhibits a very intense band between 0 and 1.5 eV and a much weaker band between 2 and 4 eV. The intensity of the latter band is significantly underestimated by theory, since this band results mainly from population of highly excited states of N 2 þ [19] and of dissociative channels of N 2 2þ not included in the present calculations. As can be observed in this figure, there are only two groups of states that significantly contribute to the lower band, namely, those leading to Nð 2 DÞ þ N þ ð 3 PÞ and Nð 2 PÞ þ N þ ð 3 PÞ, while practically all dissociative ionization channels included in our calculations contribute to the upper band.…”

Section: Resultsmentioning

confidence: 74%

“…A similar approach exploiting narrow band XUV radiation has been used to investigate autoionization in O 2 [17], as well as the creation of highly excited states in N 2 [18]. Dissociative ionization of N 2 was further studied in a recent work applying femtosecond time-resolved photoelectron and photoion spectroscopy using a tabletop XUV time-compensating monochromator [19]. The major drawback of using attosecond pulse trains is the reduced temporal resolution associated with recursive excitation events.…”

Section: Introductionmentioning

confidence: 99%

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Mapping the Dissociative Ionization Dynamics of Molecular Nitrogen with Attosecond Time Resolution

et al. 2015

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Studying the interaction of molecular nitrogen with extreme ultraviolet (XUV) radiation is of prime importance to understand radiation-induced processes occurring in Earth’s upper atmosphere. In particular, photoinduced dissociation dynamics involving excited states of N2+ leads to N and N+ atomic species that are relevant in atmospheric photochemical processes. However, tracking the relaxation dynamics of highly excited states of N2+ is difficult to achieve, and its theoretical modeling is notoriously complex. Here, we report on an experimental and theoretical investigation of the dissociation dynamics of N2+ induced by isolated attosecond XUV pulses in combination with few-optical-cycle near-infrared/visible (NIR/VIS) pulses. The momentum distribution of the produced N+ fragments is measured as a function of pump-probe delay with subfemtosecond resolution using a velocity map imaging spectrometer. The time-dependent measurements reveal the presence of NIR/VIS-induced transitions between N2+ states together with an interference pattern that carries the signature of the potential energy curves activated by the XUV pulse. We show that the subfemtosecond characterization of the interference pattern is essential for a semiquantitative determination of the repulsive part of these curves

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Section: Resultsmentioning

confidence: 74%

Section: Introductionmentioning

confidence: 99%

Mapping the Dissociative Ionization Dynamics of Molecular Nitrogen with Attosecond Time Resolution

et al. 2015

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“…Recent studies showed how femtosecond VUV and XUV radiation can be used to reveal transient nuclear and electron dynamics in diatomic molecules [8][9][10][11][12] as well as in more complex molecular systems [13,14]. To probe such dynamics, the majority of the pump-probe-style experiments accomplished to date utilize not only pairs of XUV-IR pulses [8,[15][16][17][18], but also a combination of VUV-XUV pulses [19][20][21][22].…”

Section: Introductionmentioning

confidence: 99%

Mapping and controlling ultrafast dynamics of highly excited H2 molecules by VUV-IR pump-probe schemes

et al. 2017

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We used ultrashort femtosecond vacuum ultraviolet (VUV) and infrared (IR) pulses in a pump-probe scheme to map the dynamics and nonequilibrium dissociation channels of excited neutral H 2 molecules. A nuclear wave packet is created in the B 1 + u state of the neutral H 2 molecule by absorption of the ninth harmonic of the driving infrared laser field. Due to the large stretching amplitude of the molecule excited in the B 1 + u electronic state, the effective H 2 + ionization potential changes significantly as the nuclear wave packet vibrates in the bound, highly electronically and vibrationally excited B potential-energy curve. We probed such dynamics by ionizing the excited neutral molecule using time-delayed VUV-or-IR radiation. We identified the nonequilibrium dissociation channels by utilizing three-dimensional momentum imaging of the ion fragments. We found that different dissociation channels can be controlled, to some extent, by changing the IR laser intensity and by choosing the wavelength of the probe laser light. Furthermore, we concluded that even in a benchmark molecular system such as H 2 *, the interpretation of the nonequilibrium multiphoton and multicolor ionization processes is still a challenging task, requiring intricate theoretical analysis.

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“…We attribute the strongest feature (shaded blue) to low kinetic energy N + 2 ions and predissociation of the N + 2 C 2 Σ + u state [51]. The contribution shaded in green has previously been assigned to dissociation from the F 2 Σ + g state, and the features in the area shaded in orange are associated with dissociation from the highly-excited Rydberg-like states of N + 2 and the H band [51][52][53]. Figure 6c,f shows the photoelectron momentum distribution and the photoelectron kinetic energy spectrum, respectively.…”

Section: Data Acquisitionmentioning

confidence: 95%

“…The much weaker contributions of the other cationic and dicationic states are not shown for clarity [53,54,56,57]. The signal at kinetic energies smaller than 1 eV can be assigned to highly excited inner valence states of N + 2 and possibly the first electronic states of N 2+ 2 [52,53,57]. As mentioned earlier, in order to extract information about the correlation between the different single-shot datasets, it is important that the sets are acquired simultaneously and can be analyzed in a synchronized fashion.…”

Section: Data Acquisitionmentioning

confidence: 99%

A Versatile Velocity Map Ion-Electron Covariance Imaging Spectrometer for High-Intensity XUV Experiments

et al. 2018

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We report on the design and performance of a velocity map imaging (VMI) spectrometer optimized for experiments using high-intensity extreme ultraviolet (XUV) sources such as laser-driven high-order harmonic generation (HHG) sources and free-electron lasers (FELs). Typically exhibiting low repetition rates and high single-shot count rates, such experiments do not easily lend themselves to coincident detection of photo-electrons and -ions. In order to obtain molecular frame or reaction channel-specific information, one has to rely on other correlation techniques, such as covariant detection schemes. Our device allows for combining different photo-electron and -ion detection modes for covariance analysis. We present the expected performance in the different detection modes and present the first results using an intense high-order harmonic generation (HHG) source. of their impact coordinates on the detector, as well as from the flight time, acquired by means of, e.g., delay-line detectors. REMI gives access to complete, correlated, 3D velocity information of all particles detected in coincidence, as long as the count rates are sufficiently low (<1 event/shot) to avoid detecting fragments from more than one target atom or molecule on the same shot.With high-intensity sources, the repetition rates are typically low, while the single-shot count rates can be very high, which in many cases makes it difficult to use techniques relying on detecting coincidences. Another approach is to use the so-called velocity map imaging (VMI) technique [21], which uses an extraction field configuration that makes the impact coordinates on the detector independent of the location of the ionization event within the interaction volume, as well as of the momentum along the detector axis. This allows for the use of a micro-channel plate (MCP) and a phosphor screen where the impact of a large number of particles can be accumulated on every shot. Under the condition of cylindrical symmetry of the ionization process, the initial three-dimensional momentum distribution of the particles can be recovered from the measured two-dimensional projection using numerical inversion procedures [22,23].There are several demonstrations of using VMI, under low count rate conditions, for photoelectron-photoion coincidence spectroscopy (PEPICO) [24], for example using electron VMI combined with ion time-of-flight (TOF), ion VMI together with electron spectroscopy and electron VMI with ion VMI [25][26][27][28][29].An obvious drawback of VMI in high count rate conditions is that one cannot rely on coincidence detection for extracting information about different electrons or ions coming from the same target molecule. An elegant way to overcome this lack of correlated information in VMI, without sacrificing the high count rates, is to use covariance mapping [30]. Briefly, for any two variables, X ], sampled synchronously in a repetitive measurement, one can calculate the covariance, which is a measure of how well correlated the variations of the two variables are. C...

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Dynamics of N₂ Dissociation upon Inner-Valence Ionization by Wavelength-Selected XUV Pulses

Cited by 57 publications

References 28 publications

Mapping the Dissociative Ionization Dynamics of Molecular Nitrogen with Attosecond Time Resolution

Mapping the Dissociative Ionization Dynamics of Molecular Nitrogen with Attosecond Time Resolution

Mapping and controlling ultrafast dynamics of highly excited H2 molecules by VUV-IR pump-probe schemes

A Versatile Velocity Map Ion-Electron Covariance Imaging Spectrometer for High-Intensity XUV Experiments

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Dynamics of N2 Dissociation upon Inner-Valence Ionization by Wavelength-Selected XUV Pulses

Cited by 57 publications

References 28 publications

Mapping the Dissociative Ionization Dynamics of Molecular Nitrogen with Attosecond Time Resolution

Mapping the Dissociative Ionization Dynamics of Molecular Nitrogen with Attosecond Time Resolution

Mapping and controlling ultrafast dynamics of highly excited H2 molecules by VUV-IR pump-probe schemes

A Versatile Velocity Map Ion-Electron Covariance Imaging Spectrometer for High-Intensity XUV Experiments

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Dynamics of N₂ Dissociation upon Inner-Valence Ionization by Wavelength-Selected XUV Pulses