Ultrafast nonadiabatic dynamics probed by nitrogen K-edge absorption spectroscopy

Northey, Thomas; Norell, Jesper; Fouda, Adam E. A.; Besley, Nicholas A.; Odelius, Michael; Penfold, Thomas J.

doi:10.1039/c9cp03019k

Cited by 43 publications

(56 citation statements)

References 67 publications

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“…A temporal resolution of 11 fs is measured in a pump-probe experiment. This duration is already 8/10 enough to consider the observation of ultrafast chemical dynamics at the C K-edge 30,31,52,58 . Improved CEP stability and feedback control over the delay will allow attosecond transient absorption experiments in the SXR in the future.…”

Section: Discussionmentioning

confidence: 99%

Efficient table-top dual-wavelength beamline for ultrafast transient absorption spectroscopy in the soft X-ray region

Barreau

Ross

Garg

et al. 2020

Sci Rep

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We present a table-top beamline providing a soft X-ray supercontinuum extending up to 350 eV from high-order harmonic generation with sub-13 fs 1300 nm driving pulses and simultaneous production of sub-5 fs pulses centered at 800 nm. Optimization of the high harmonic generation in a long and dense gas medium yields a photon flux of ~2 x 10 7 photons/s/1% bandwidth at 300 eV. The temporal resolution of X-ray transient absorption experiments with this beamline is measured to be 11 fs for 800 nm excitation. This dual-wavelength approach, combined with high flux and high spectral and temporal resolution soft X-ray absorption spectroscopy, is a new route to the study of ultrafast electronic dynamics in carbon-containing molecules and materials at the carbon K-edge. 2/10 Description of the table-top dual-wavelength beamlineThe beamline is summarized in Figure 1. It uses a 13 mJ , 800 nm, 30 fs, 1 kHz Ti:Sapphire laser (Coherent Legend Elite Duo), whose energy is split into 11 mJ +2 mJ to produce the probe and pump pulses, respectively, used in time-resolved X-ray transient absorption experiments. This section details the simultaneous compression of SWIR (centered at 1300 nm or 1400 nm) and visible-near infrared (centered at 800 nm) pulses, and the characteristics of the soft X-ray spectrometer. Production of few-cycle short-wave infrared pulsesThe few-cycle pulses centered at 1300 nm in the SWIR are produced using an OPA followed by spectral broadening in a hollow-core fiber filled with a rare gas 35 and compression with chirped mirrors 36 . The 11 mJ 800 nm beam is further split into 0.5 mJ and 10.5 mJ for use in a two-stage OPA, which converts the 800 nm to SWIR (1300 nm). The two-stage system is obtained from Light Conversion and is designed to provide CEP stability of the signal pulses. The first stage is a low energy OPA (TOPAS Prime), pumped by 0.5 mJ, which provides 90 J of 2 m pulses in the idler. Due to the parametric amplification process, the idler pulses are passively CEP stabilized, with a stability of <200 mrad. They are then used as the seed for the white light generation in a second, high energy, OPA (HE-TOPAS) pumped with the remaining 10.5 mJ of 800 nm light. This design should ensure the CEP stability of the signal pulses over the 1200-1600 nm tunable range of the OPA, regardless of the CEP stability of the pump laser. However, the following results are obtained with a CEP-averaged signal pulse. The 2.8 mJ, 1300 nm, 40 fs output is focused with a 2-m focusing mirror to a focal size of 390 m (at 1/e 2 ) at the entrance of a 3-m-long, 700-m-inner diameter stretched hollow-core fiber (HCF) filled with 0.4 bar of argon (Few-Cycle Inc.). The ratio of beam

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Section: Discussionmentioning

confidence: 99%

Efficient table-top dual-wavelength beamline for ultrafast transient absorption spectroscopy in the soft X-ray region

Barreau

Ross

Garg

et al. 2020

Sci Rep

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“…a few minutes for the calculation of an EXAFS spectrum). While the computational cost of such theoretical treatments is not prohibitive for a few calculations, it becomes so for the most challenging systems, e.g., disordered/amorphous systems, such as the surface of an operando catalyst [14][15][16], or dynamical processes [17][18][19][20][21]. A huge number of different and dynamically-evolving absorption sites must be modelled for a quantitative analysis, but to treat theoretically every possible chemically-inequivalent absorption site (or even to sample a meaningful number of such sites) is computationally challenging, resource-intensive, and time-consuming.…”

Section: Introductionmentioning

confidence: 99%

The Role of Structural Representation in the Performance of a Deep Neural Network for X-ray Spectroscopy

2020

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An important consideration when developing a deep neural network (DNN) for the prediction of molecular properties is the representation of the chemical space. Herein we explore the effect of the representation on the performance of our DNN engineered to predict Fe K-edge X-ray absorption near-edge structure (XANES) spectra, and address the question: How important is the choice of representation for the local environment around an arbitrary Fe absorption site? Using two popular representations of chemical space—the Coulomb matrix (CM) and pair-distribution/radial distribution curve (RDC)—we investigate the effect that the choice of representation has on the performance of our DNN. While CM and RDC featurisation are demonstrably robust descriptors, it is possible to obtain a smaller mean squared error (MSE) between the target and estimated XANES spectra when using RDC featurisation, and converge to this state a) faster and b) using fewer data samples. This is advantageous for future extension of our DNN to other X-ray absorption edges, and for reoptimisation of our DNN to reproduce results from higher levels of theory. In the latter case, dataset sizes will be limited more strongly by the resource-intensive nature of the underlying theoretical calculations.

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“…In the case of spectroscopy, this task requires the combination of electronic structure calculations and nonadiabatic dynamics simulations. This technique has been recently employed for the simulation of TR X-ray absorption [12][13][14][15][16][17] and emission spectra. 12 While X-ray spectroscopies are local, element-specific probes by their nature, X-ray scattering is global, i.e., arising from all electrons in the sample.…”

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confidence: 99%

Simulation of ultrafast excited-state dynamics and elastic x-ray scattering by quantum wavepacket dynamics

Pápai

Rozgonyi

Penfold

et al. 2019

The Journal of Chemical Physics

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Ultrafast nonadiabatic dynamics probed by nitrogen K-edge absorption spectroscopy

Abstract: Quantum dynamics simulations are used to simulate the ultrafast X-ray Absorption Near-Edge Structure (XANES) spectra of photoexcited pyrazine including two strongly coupled electronically excited states and four normal mode degrees of freedom.

Cited by 43 publications

References 67 publications

Efficient table-top dual-wavelength beamline for ultrafast transient absorption spectroscopy in the soft X-ray region

Efficient table-top dual-wavelength beamline for ultrafast transient absorption spectroscopy in the soft X-ray region

The Role of Structural Representation in the Performance of a Deep Neural Network for X-ray Spectroscopy

Simulation of ultrafast excited-state dynamics and elastic x-ray scattering by quantum wavepacket dynamics

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