Femtosecond dynamics of dissociation and recombination in solvent cages

Liu, Qianli; Wang, Juen-Kai; Zewail, Ahmed H.

doi:10.1038/364427a0

Cited by 161 publications

(99 citation statements)

References 29 publications

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“…8 Fluorescence spectroscopy is often used to identify the products of photochemical reactions in clusters, [9][10][11][12][13][14][15][16][17][18][19] and femtosecond laser excitation provides information on the time evolution of reactions. 20,21 Femtosecond photoelectron spectroscopy on mass selective iodine Ar anion clusters showed that a solvation shell of 20 Ar atoms was sufficient to induce recombination of the iodine fragments 21,20 and similar experiments on iodine in neutral Ar clusters revealed that caging was completed within 10 −12 s. [22][23][24] A thorough investigation of the cage effect of hydrogen halides doped into the interior or onto the surface of clusters and aligned in a static electric and a laser field was recently undertaken by Buck and co-workers. [25][26][27][28][29][30] They measured the kinetic energy of the hydrogen atom as a function of the orientation and showed that the dissociation of hydrogen halides can even be inhibited on the cluster surface because the light hydrogen carries almost all the kinetic energy and is caged by the cluster and the heavy halogen atom.…”

Section: Introductionmentioning

confidence: 99%

Photochemical processes in doped argon-neon core-shell clusters: The effect of cage size on the dissociation of molecular oxygen

Laarmann

Wabnitz

Haeften

et al. 2008

The Journal of Chemical Physics

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The caging effect of the host environment on photochemical reactions of molecular oxygen is investigated using monochromatic synchrotron radiation and spectrally resolved fluorescence. Oxygen doped clusters are formed by coexpansion of argon and oxygen, by pickup of molecular oxygen or by multiple pickup of argon and oxygen by neon clusters. Sequential pickup provides radially ordered core-shell structures in which a central oxygen molecule is surrounded by argon layers of variable thickness inside large neon clusters. Pure argon and core-shell argon-neon clusters excited with ϳ12 eV monochromatic synchrotron radiation show strong fluorescence in the vacuum ultraviolet ͑vuv͒ spectral range. When the clusters are doped with O 2 , fluorescence in the visible ͑vis͒ spectral range is observed and the vuv radiation is found to be quenched. Energy-resolved vis fluorescence spectra show the 2 1 ⌺ + → 1 1 ⌺ + ͑ArO͑ 1 S͒ → ArO͑ 1 D͒͒ transition from argon oxide as well as the vibrational progression A Ј 3 ⌬ u ͑ Ј=0͒ → X 3 ⌺ g − ͑ Љ͒ of O 2 indicating that molecular oxygen dissociates and occasionally recombines depending on the experimental conditions. Both the emission from ArO and O 2 as well the vuv quenching by oxygen are found to depend on the excitation energy, providing evidence that the energy transfer from the photoexcited cluster to the embedded oxygen proceeds via the O 2 + ground state. The O 2 + decays via dissociative recombination and either reacts with Ar resulting in electronically excited ArO or it recombines to O 2 within the Ar cage. Variation of the Ar layer thickness in O 2 -Ar-Ne core-shell clusters shows that a stable cage is formed by two solvation layers.

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Section: Introductionmentioning

confidence: 99%

Photochemical processes in doped argon-neon core-shell clusters: The effect of cage size on the dissociation of molecular oxygen

Laarmann

Wabnitz

Haeften

et al. 2008

The Journal of Chemical Physics

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“…[1][2][3][4][5][6][7][8] We focus on dynamics of the simplest limit, the triatomic van der Waals ͑vdW͒ complex ArI 2 . When I 2 is excited to the B electronic state, [1][2][3][4] vibrational predissociation ͑VP͒, VP is transfer of vibrational energy from I 2 to the ArI bonds which subsequently break.…”

Section: Introductionmentioning

confidence: 99%

Quantum dynamics of ArI2 vibrational predissociation including low total angular momenta: The role of intramolecular vibrational energy redistribution

Roncero

Gray

1996

The Journal of Chemical Physics

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Full-dimensional quantum dynamics calculations on ArI 2 (B,v i ) vibrational predissociation with total angular momenta Jϭ0, 1, and 2 are presented. Models based on a few interacting states are shown to reproduce important aspects of the dynamics, confirming that vibrational predissociation is mediated by a few-state intramolecular vibrational energy redistribution effect. As a consequence, vibrational predissociation rate constants exhibit large oscillations with v i , the initial I 2 vibrational quantum number in the complex. The qualitative effect persists when alternative choices for the interaction potential parameters are considered. Similarly, despite the importance of Coriolis coupling, the effect persists as J is varied from 0 to 2. We also discuss how the effect may be difficult to observe in typical experiments that involve higher J values.

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“…The present effect where the argon atoms that have to be pushed away, are hindering the molecular deformations differ from the usual caging dynamics of a dissociating molecule by a solvent, as exemplified by the dissociation of I 2 in rare gases [57,58] or that of Cl 2 molecules within large xenon clusters [59]. The caging dynamics of molecular dissociation appears indeed as a hard sphere collision of the departing halogen atoms with the surrounding atoms.…”

Section: Short Time Delays: a Chistera Effect On The Passage Near The CImentioning

confidence: 99%

Dynamics of excited tetrakis(dimethylamino)ethylene solvated by argon atoms

et al. 2004

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The supersonic expansion of a mixture of the title molecule (TDMAE) with argon generates a beam carrying a log-normal distribution of TDAME(Ar) n clusters, broadly centered atn ≈ 60. The femtosecond pump-probe technique is used to investigate the excited state dynamics of these clusters up to a 220 ps delay between the pump and the probe. This documents the effect of the argon environment on the TDMAE dynamics. The TDMAE molecule is excited in the valence state V within the cluster by the pump laser at 266 nm. It undergoes deformation in the excited potential energy surface that brings the initial wavepacket to a conical intersection (CI) where the electronic configuration of the molecule switches to a Zwitterionic configuration Z. Compared to the behaviour of free TDMAE, the effect of the argon environment is a slow down of the wavepacket movement and an increase of the time scale of the V-Z energy transfer from 300 fs to 400 ± 50 fs. This slow down effect, that we call a chistera effect, differs from a standard cage effect. Here, the deforming molecule does not experience a hard sphere collision with the argon cage, rather it pushes it away. Furthermore, umbrella oscillations of the dimethylamino groups are excited when the initial wavepacket passes the CI region. Because of the argon environment, the sharp 250 fs oscillation period of the free molecules is transformed into a broad structure of 40 fs width (FWHM) centred at about 240 fs. In addition, breathing oscillations of the argon environment with respect to the TDMAE molecule are observed with a period of 410 ± 40 fs. Finally, long delays between the pump and the probe lasers allow us to investigate the non radiative energy transfer from the Z electronic configuration of TDMAE(Ar) n to a charge transfer state. The effect of the evaporation of argon atoms in the neutral and the ionised clusters has been taken into account, as its time scale accompanies that of the observed phenomena.

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Femtosecond dynamics of dissociation and recombination in solvent cages

Cited by 161 publications

References 29 publications

Photochemical processes in doped argon-neon core-shell clusters: The effect of cage size on the dissociation of molecular oxygen

Photochemical processes in doped argon-neon core-shell clusters: The effect of cage size on the dissociation of molecular oxygen

Quantum dynamics of ArI2 vibrational predissociation including low total angular momenta: The role of intramolecular vibrational energy redistribution

Dynamics of excited tetrakis(dimethylamino)ethylene solvated by argon atoms

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