Real-time probing of reactions in clusters

Breen, J. J.; Peng, Lawrence W.; Willberg, D. M.; Heikal, Ahmed A.; Cong, Peijun; Zewail, Ahmed H.

doi:10.1063/1.458384

Cited by 116 publications

(57 citation statements)

References 33 publications

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“…16 The ensuing free jet was perpendicularly crossed at a distance of6 mm (xld::::::: 75) by the spatially overlapped pump and probe laser beams. Fluorescence was collected, spatially filtered, and imaged onto a filtered photomultiplier tube.…”

Section: ----Axmentioning

confidence: 99%

Direct observation of the picosecond dynamics of I2–Ar fragmentation

Breen

Willberg

Gutmann

et al. 1990

The Journal of Chemical Physics

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The fragmentation of van der Waals (vdW) complexes offers an opportunity for studying the half-collision dynamics in well-defined systems. In previous work from this laboratory, we have studied, 1 in real time, the dynamics of the "hair' and the "full" collision, but we had no results on the diatom-rare gas small vdW complexes. Iodine with rare gases I 2 -M (M =He, Ne, and Ar) are of particular interest for a number of reasons.First, the IrM vibrational dynamics are rather simple; an iodine stretch, and two van der Waals' stretch and bend modes. Second, from the pioneering work 2 on the spectroscopy, there is a wealth of data that provide the vibrational structure, geometry, and the photochemistry of these systems. Third, the I 2 real-time dynamics on the fs-ps time scale have already been reported. 3 Finally, unlike the case of large molecules, theory is quite advanced 4 for these smaller systems, and there is hope for a detailed understanding of IVR and vibrational predissociation. Real-time studies of large vdW complexes have been reported for isoquinoline, I tetrazine (in sl and So)' 5 phenoV cresoV perylene, 6 stilbene, 1 • 7 aniline, 8 and (N0) 2 (in S 0 ), 9 and only recently have results become available for the family of halogens. With nanosecond lasers, the lifetime of I CI-Ne in its A state was measured to be 3 ± 2 ns for v' = 14 by the Lester group. 10 As discussed below, other methods, such as linewidth measurements, have been used to deduce vibrational predissociation lifetimes.In this communication, we report direct picosecond measurements of the state-to-state rates obtained from real-time observation of fragment I! molecules in the reaction I * 1----AxOn the picosecond time scale, we observe the exponential buildup of nascent I! population, and the experiments show a slow "inverse" dependence on v', i.e., a slight decrease in the rate with increased v'. The results give the homogeneous width of the initial state, and establish the time scale for the dynamics in the channels, I! + Ar (vibrational predissociation, kv) and I + I + Ar (electronic predissociation, ke). The rise times measured in our experiments correspond to T = (kv + ke)-1 , and for the above reaction, n = 21 and 18 in the B state of I 2 (or Iz-Ar ). The binding energy oflz-Ar is known to be between 220 to 226 em-1 ; at the vibrational levels that we access in this experiment, this requires the redistribution of at least three quanta of energy from the iodine to the van der Waals bond in order to induce dissociation. (The geometry is not known from our experiments, but we draw it to be nonlinear, as suggested by previous work. 11 ) The experiments required a special care, because of inherent difficulties in preparing "clean" complexes ( usually much weaker than the parent species) with no background and at the same time detecting them with highenough sensitivity for state-to-state measurements on the picosecond time scale. The pump-probe scheme applied in these molecular beam experiments is similar to that used in earlier developm...

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Section: ----Axmentioning

confidence: 99%

Direct observation of the picosecond dynamics of I2–Ar fragmentation

Breen

Willberg

Gutmann

et al. 1990

The Journal of Chemical Physics

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“…The first system we studied was that of 1-naphthol (1-NpOH) as the acid and ammonia, piperidine, or water as the base solvent, with the number (n) of solvent molecules varying (20)(21)(22). Time-resolved fluorescence and ps and fs ionization mass spectrometry were carried out to investigate the dynamics of each cluster.…”

Section: Acid-base Proton-transfer Reactionsmentioning

confidence: 99%

“…The scope of phenomena studied varied, from the influence of one-atom solvation and caging (13)(14)(15)(16)(17)(18)(19), to stepwise solvation of acid-base (20)(21)(22) and isomerization reactions (23,24) in clusters of up to 30 solvent molecules. Both electron (25)(26)(27)(28) and proton transfer (20)(21)(22)29) processes were also studied, elucidating for the former one of the classics for Mulliken's dative bonded complexes, that of benzene-iodine, and for the latter the dynamics of single and double proton transfer.…”

mentioning

confidence: 99%

“…Both electron (25)(26)(27)(28) and proton transfer (20)(21)(22)29) processes were also studied, elucidating for the former one of the classics for Mulliken's dative bonded complexes, that of benzene-iodine, and for the latter the dynamics of single and double proton transfer. With mass selection, we investigated ionic clusters, the premier being solvated electrons (30) and dioxygen anions (31)(32)(33); both are important in biological activities.…”

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confidence: 99%

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Dynamics of clusters: From elementary to biological structures

Cheng¹,

Baskin

Zewail³

2006

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

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Between isolated atoms or molecules and bulk materials there lies a class of unique structures, known as clusters, that consist of a few to hundreds of atoms or molecules. Within this range of ''nanophase,'' many physical and chemical properties of the materials evolve as a function of cluster size, and materials may exhibit novel properties due to quantum confinement effects. Understanding these phenomena is in its own rights fundamental, but clusters have the additional advantage of being controllable model systems for unraveling the complexity of condensed-phase and biological structures, not to mention their vanguard role in defining nanoscience and nanotechnology. Over the last two decades, much progress has been made, and this short overview highlights our own involvement in developing cluster dynamics, from the first experiments on elementary systems to model systems in the condensed phase, and on to biological structures.I n the early 1980s, our research group at Caltech began exploring real-time dynamics of clusters (1-5) by studying time-resolved spectroscopy, with picosecond (ps) and then femtosecond (fs) resolution (6-8), in molecular jets and beams (9, 10). These first results (ref. 11; for commentary, see ref. 12) opened the door for many more applications as they clearly elucidated in real time the influence of microsolvation and stepwise solvation effects on reactivity and photophysical processes in clusters (12). The ultimate goal we had in mind was to ''bridge'' the gap between the isolatedmolecule behavior and that in the bulk phase, and to understand at a microscopic level the influence of solvent on reactions.The scope of phenomena studied varied, from the influence of one-atom solvation and caging (13)(14)(15)(16)(17)(18)(19), to stepwise solvation of acid-base (20-22) and isomerization reactions (23, 24) in clusters of up to 30 solvent molecules. Both electron (25-28) and proton transfer (20)(21)(22)29) processes were also studied, elucidating for the former one of the classics for Mulliken's dative bonded complexes, that of benzene-iodine, and for the latter the dynamics of single and double proton transfer. With mass selection, we investigated ionic clusters, the premier being solvated electrons (30) and dioxygen anions (31-33); both are important in biological activities. For chemical reactions, we used this approach of complexation to study bimolecular reactive (34-37) and nonreactive (38) scattering, and, by analogy, biomolecular structures exhibiting dative bonding and involved in molecular recognition (39-41). A descriptive outline of the work over two decades is given in Fig. 1, including relevant references (refs. 6-8 and 13-49; ref. 50 and references therein). In what follows, we only highlight some prototypical examples. Bimolecular ReactionsEarly in the development of fs transitionstate spectroscopy (51) it was possible to directly probe the transition state by realtime clocking of a unimolecular reaction (half collision): ABC* 3 A⅐⅐⅐B⅐⅐⅐C* ‡ 3 AB ϩ C. For a bimolecular reacti...

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“…Recently, picosecond pump/probe experiments employing mass selective detection were reported for jet-cooled l-naphthol 8 and phenol t1 clustered with water and ammonia. The reported observations for water clusters are in agreement with the steady state results 6 ' 17 : no proton transfer occurs even for n > 20.…”

Section: Hv (I)mentioning

confidence: 99%