Non-intrusive detection of combustion intermediates by photoionization via Rydberg states and microwave backscattering

Rudakov, Fedor; Gao, Yubing; Cheng, Xinxin; Weber, Peter M.

doi:10.1016/j.combustflame.2016.06.005

Cited by 9 publications

(5 citation statements)

References 40 publications

(44 reference statements)

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“…Depending on the structure, the calculated binding energy spans the range from 2.92 to 3.04 eV, which is in close agreement with the experimental data ranging from 2.87 to 2.97 eV. A systematic deviation of 0.07 eV between experimental and computed binding energy is typical for tertiary amines , and has also been found for the 3p states of the methyl radical . The close agreement between experimentally measured and computed binding energy further confirms the assignment of the spectrum to the 3s Rydberg state.…”

supporting

confidence: 81%

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Observation of Structural Wavepacket Motion: The Umbrella Mode in Rydberg-Excited N-Methyl Morpholine

Zhang

Deb

Jónsson

et al. 2017

J. Phys. Chem. Lett.

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We have observed time-resolved, structural dynamics of a coherent vibrational wavepacket in Rydberg-excited N-methyl morpholine, a molecule with 48 internal degrees of freedom. The molecular structure was established by associating the time-dependent Rydberg electron binding energy, obtained from time-resolved photoionization-photoelectron spectroscopy, to the molecular structure using self-interaction corrected density functional calculations. Optical excitation at 226 nm launches an oscillatory wavepacket in the amine umbrella coordinate with a 650 fs period. Even though the Franck-Condon excitation is at an angle of 17°, the wavepacket settles into an oscillation between 4° and -10° within a fraction of a vibrational period and then dephases with a time constant of 750 fs.

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supporting

confidence: 81%

“…A systematic deviation of 0.07 eV between experimental and computed binding energy is typical for tertiary amines 25,26 and has also been found for the 3p states of the methyl radical. 33 The close agreement between experimentally measured and computed binding energy further confirms the assignment of the spectrum to the 3s Rydberg state.…”

supporting

confidence: 65%

Observation of Structural Wavepacket Motion: The Umbrella Mode in Rydberg-Excited N-Methyl Morpholine

Zhang

Deb

Jónsson

et al. 2017

J. Phys. Chem. Lett.

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“…Here a summary is given to the previously demonstrated species detections using single ultraviolet and visible laser beam for REMPI. It should be noted that the multiple laser wavelengths can be used to probe various atomic and molecular resonance states [16], which is not included here (table 1).…”

Section: Resonance-enhanced Multiphoton Ionization (Rempi)mentioning

confidence: 99%

Coherent microwave scattering from resonance enhanced multi-photon ionization (radar REMPI): a review

Shneider

Miles

2021

Plasma Sources Sci. Technol.

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Coherent microwave scattering from laser-induced plasmas, including weakly ionized plasma, laser sparks, multiphoton ionization, and resonance enhanced multi-photon ionizations (radar REMPI) has achieved much successes in plasma, reactive and nonreactive flow diagnostics. Under illumination of microwaves (radar), electrons inside the laser-induced plasma oscillate with the electric field of the microwave and re-radiate from the electrons forming coherent scattering. In the far-field approximation, the microwave scattering from the small volume plasma reflects the generation and evolution of unbounded electrons inside the plasma, when the microwave wavelength is much greater than the size of the plasma and the skin layer depth at the microwave frequency is larger than the size of the plasma. Laser excitation schemes, microwave detection methods, calibration of microwave scattering, and the novel applications of the technique have been significantly expanded and improved. This review paper summarizes physical principles, various REMPI excitation schemes for atomic and molecular species, and temperature measurements in plasma and reactive flows. Discussions on new research directions and applications are given at the end.

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“…A recent study monitored the spatial distribution of methyl radicals in a variety of flames. 300 Finally, it should be mentioned that there are other means for using internally generated electrons for probing molecular structures on femtosecond time scales. With the advent of attosecond spectroscopy, it is possible to use correlations in high harmonic generation with respect to the generated harmonic profile to image the electronic wave function.…”

Section: Chemical Reviewsmentioning

confidence: 99%

“…As a result, ionization transitions from Rydberg states are measured as well-localized peaks even in systems where valence electronic transitions are broadened by extensive vibrational congestion. , Because Rydberg ionization spectra can also be measured at atmospheric pressure, it has been possible to apply the method to investigate transient radicals in flames. A recent study monitored the spatial distribution of methyl radicals in a variety of flames …”

Section: Breaking the Picosecond Barrier To Atomically Resolved Dynamicsmentioning

confidence: 99%

Capturing Chemistry in Action with Electrons: Realization of Atomically Resolved Reaction Dynamics

2017

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One of the grand challenges in chemistry has been to directly observe atomic motions during chemical processes. The depiction of the nuclear configurations in space-time to understand barrier crossing events has served as a unifying intellectual theme connecting the different disciplines of chemistry. This challenge has been cast as an imaging problem in which the technical issues reduce to achieving not only sufficient simultaneous space-time resolution but also brightness for sufficient image contrast to capture the atomic motions. This objective has been met with electrons as the imaging source. The review chronicles the first use of electron structural probes to study reactive intermediates, to the development of high bunch charge electron pulses with sufficient combined spatial-temporal resolution and intensity to literally light up atomic motions, as well as the means to characterize the electron pulses in terms of temporal brightness and image reconstruction. The use of femtosecond Rydberg spectroscopy as a novel means to use internal electron scattering within the molecular reference frame to obtain similar information on reaction dynamics is also discussed. The focus is on atomically resolved chemical reaction dynamics with pertinent references to work in other areas and forms of spectroscopy that provide additional information. Effectively, we can now directly observe the far-from-equilibrium atomic motions involved in barrier crossing and categorize chemistry in terms of a power spectrum of a few dominant reaction modes. It is this reduction in dimensionality that makes chemical reaction mechanisms transferrable to seemingly arbitrarily complex (large N) systems, up to molecules as large as biological macromolecules (N > 1000 atoms). We now have a new way to reformulate reaction mechanisms using an experimentally determined dynamic mode basis that in combination with recent theoretical advances has the potential to lead to a new conceptual basis for chemistry that forms a natural link between structure and dynamics.

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Non-intrusive detection of combustion intermediates by photoionization via Rydberg states and microwave backscattering

Cited by 9 publications

References 40 publications

Observation of Structural Wavepacket Motion: The Umbrella Mode in Rydberg-Excited N-Methyl Morpholine

Observation of Structural Wavepacket Motion: The Umbrella Mode in Rydberg-Excited N-Methyl Morpholine

Coherent microwave scattering from resonance enhanced multi-photon ionization (radar REMPI): a review

Capturing Chemistry in Action with Electrons: Realization of Atomically Resolved Reaction Dynamics

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