The Nature of Simple Photodissociation Reactions in Liquids on Ultrafast Time Scales

Harris, A. L.; Brown, J. K.; Harris, Charles B.

doi:10.1146/annurev.pc.39.100188.002013

Cited by 370 publications

(239 citation statements)

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“…As a prototype for condensed phase nonadiabatic dynamics, the B( 3 P 0u ) state of molecular iodine has been the subject of extensive time domain studies in liquids, [1][2][3][4] in clusters, 5,6 under high pressure, 7 and in rare gas matrixes. [8][9][10] Complementary to these measurements is the understanding of the frequency domain spectra of the molecule in condensed phases.…”

Section: Introductionmentioning

confidence: 99%

Resonant Raman, Hot, and Cold Luminescence of Iodine in Rare Gas Matrixes

et al. 2000

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Spontaneous light emission (SLE) spectra induced by continuous wave excitation of iodine in rare gas matrixes is analyzed from the perspective of semiclassical molecular dynamics. The three-time correlation functions that describe the process are interpreted in terms of time circuits, where the reversibility of mechanics along specified paths establishes the distinction between resonant Raman (RR) and fluorescence. The observed hot luminescence (fluorescence from the vibrationally over-damped period of dynamics) is simulated, and the underlying dynamics analyzed to describe vibrational dephasing, formation of stationary states, and predissociation of I 2 (B) in matrixes. The extracted predissociation time of 3-5 ps in matrixes agrees with time-domain measurements. The analysis allows the interpretation of liquid phase spectra which contain both structured and unstructured SLE as strictly RR, suggesting that the unstructured component is due to linear complexes. The spectra also contain vibrationally relaxed emissions from the cage-bound, doubly spin-orbit excited

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Section: Introductionmentioning

confidence: 99%

Resonant Raman, Hot, and Cold Luminescence of Iodine in Rare Gas Matrixes

et al. 2000

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“…In the condensed phase, the dynamics are not only determined by the potential energy surfaces of the reactantproduct species, but the surrounding solvent also plays a crucial role in modifying the energies of all species and imposing the reaction pathway (14). Because the diffraction method is sensitive to all species in the solution, the changes in scattering due to photoexcitation fall in several classes of diffraction modifications: (i) the structural changes in the solutes by the photoreaction, (ii) the changes of cage structure, and (iii) the solvent's structural change due to the energy transfer [such as heating and thermal expansion (1,(15)(16)(17)(18)].…”

mentioning

confidence: 99%

Spatiotemporal reaction kinetics of an ultrafast photoreaction pathway visualized by time-resolved liquid x-ray diffraction

Kim

Lorenc

Lee

et al. 2006

Proc. Natl. Acad. Sci. U.S.A.

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We have studied the reaction dynamics for HgI2 in methanol by using time-resolved x-ray diffraction (TRXD). Although numerous time-resolved spectroscopic studies have provided ample information about the early dynamics of HgI 2, a comprehensive reaction mechanism in the solution phase spanning from picoseconds up to microseconds has been lacking. Here we show that TRXD can provide this information directly and quantitatively. Picosecond optical pulses triggered the dissociation of HgI 2, and 100-ps-long x-ray pulses from a synchrotron probed the evolving structures over a wide temporal range. To theoretically explain the diffracted intensities, the structural signal from the solute, the local structure around the solute, and the hydrodynamics of bulk solvents were considered in the analysis. The results in this work demonstrate that the determination of transient states in solution is strongly correlated with solvent energetics, and TRXD can be used as an ultrafast calorimeter. It also is shown that a manifold of structural channels can be resolved at the same time if the measurements are accurate enough and that global analysis is applied. The rate coefficients for the reactions were obtained by fitting our model against the experimental data in one global fit including all q-values and time delays. The comparison between all putative reaction channels confirms that two-body dissociation is the dominant dissociation pathway. After this primary bond breakage, two parallel channels proceed. Transient HgI associates nongeminately with an iodine atom to form HgI 2, and I2 is formed by nongeminate association of two iodine atoms.HgI2 ͉ hydrodynamics ͉ liquid phase ͉ molecular structural dynamics ͉ transient structure T he knowledge of temporally varying molecular structures during ultrafast processes is vital in understanding the mechanism and function of molecular reaction. During the last decades, the dynamics of molecular reactions have been investigated by numerous spectroscopic techniques with femtosecond time resolution. However, the direct determination, at atomic resolution, of the structural dynamics involved in such processes can only be obtained by time-resolved x-ray (1-5), electron diffraction (6-9) and x-ray absorption spectroscopy (10, 11) acting as atomic probes. The methodology of time-resolved x-ray͞electron diffraction is similar to ultrafast optical pumpprobe experiment: a femtosecond laser pulse triggers a reaction in the molecules, and a delayed electron or x-ray pulse, rather than an optical pulse as in optical spectroscopy, probes the structural evolution. The changes in the nuclear coordinates are directly recorded by varying the time delay between the laser and the x-ray͞electron pulse.Because the scattering cross section of hard x-rays is 6 orders of magnitude lower than for electrons (12, 13), time-resolved x-ray diffraction (TRXD) can penetrate condensed samples such as liquids. In the condensed phase, the dynamics are not only determined by the potential energy surfaces of the reactantp...

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“…Earlier work focused on the latter, the so-called "cage e †ect,Ï and these have been reviewed by Harris et al 2 for the liquid phase, while the reaction dynamics in media ranging from low-pressure gases to compressed liquids has been reviewed by Schroeder and Troe.3 They suggested that the cage e †ect could be due to a van der Waals molecule binding to solvent particles I 2 and it was indeed demonstrated by Saenger et al 4 and Valentini and Cross5 in molecular beam experiments that caging of I fragments occurs in the presence of one solvent particle. This "one-atom cage e †ectÏ in clusters was later studied in detail by Philippoz et al 6 More recent studies concern ultrafast pumpÈprobe spectroscopy of photodissociation in large inert clusters,7h9 in high-pressure inert gases10,11 and in rare gas matrices.12,13 These have been possible thanks to the pioneering work by Zewail and co-workers14 on gasphase iodine.…”

Section: Introductionmentioning

confidence: 99%

Ultrafast Intramolecular and Caging Dynamics of I2 in CCl4 from Resonance Raman Spectroscopy

Schwentner

Hennig

et al. 1997

J. Raman Spectrosc.

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The resonance Raman overtone progressions of in following excitation in the bound and continuum parts of I 2 CCl 4 the B state are presented. It is shown that the Raman contribution from the bound part is damped by predissociation as that of an outgoing wavepacket crossing over to the purely repulsive and B/ 1P 1u , 3P 2g , a 3P 1g aº 3R g -(0) states. The Raman data deliver information about location and time of curve crossing events which is consistent with the previous results in liquid Xe and the femtosecond pump-probe studies in liquids. For excitation in the continuum part, the Raman overtone intensities show structures which are assigned to a coherent recoil of fragments in the cage. In addition, a broad structureless emission background appears for all excitation wavelengths shorter than 570 nm, which is assigned to incoherent recoils caused by vibrational relaxation and return of the I atoms in the Franck-Condon window of the B state to the ground state.

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The Nature of Simple Photodissociation Reactions in Liquids on Ultrafast Time Scales

Cited by 370 publications

References 0 publications

Resonant Raman, Hot, and Cold Luminescence of Iodine in Rare Gas Matrixes

Resonant Raman, Hot, and Cold Luminescence of Iodine in Rare Gas Matrixes

Spatiotemporal reaction kinetics of an ultrafast photoreaction pathway visualized by time-resolved liquid x-ray diffraction

Ultrafast Intramolecular and Caging Dynamics of I2 in CCl4 from Resonance Raman Spectroscopy

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