Bimolecular reactions observed by femtosecond detachment to aligned transition states: Inelastic and reactive dynamics

Zhong, Dongping; Cheng, Po‐Yuan; Zewail, Ahmed H.

doi:10.1063/1.472606

Cited by 68 publications

(57 citation statements)

References 66 publications

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“…Under these expansion conditions, there is no evidence for the formation of CH 3 I clusters or I 2 in the mass spectrum or as additional features in the ion images, indicating that dimer formation is negligible. 5,[11][12][13] In the interaction region, the molecular beam is crossed at right angles by the laser beams.…”

Section: Methodsmentioning

confidence: 99%

“…Using this approach, the vibrationless level of the first optically active Rydberg state, namely the B 6s [2] state, was found to have a picosecond lifetime, 1, 2 while higher vibrational levels of this state were found to have significantly shorter lifetimes. [3][4][5] Recently, we have studied the predissociation of the vibrationless level of the B 6s [2] state by time-resolved photoelectron spectroscopy, 6 and in the present paper, we extend this work by using fs-REMPI (Resonant Enhanced Multiphoton Ionization) to study the fragment branching fractions and translational energy distributions. The present results can be compared with the recent results of Gitzinger et al, which were obtained by using a very similar experimental set-up.…”

Section: Introductionmentioning

confidence: 99%

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Time-resolved predissociation of the vibrationless level of the B state of CH3I

Thiré

Cireasa

Staedter

et al. 2011

Phys. Chem. Chem. Phys.

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The predissociation dynamics of the vibrationless level of the first Rydberg state 6s (B 2 E) state of CH 3 I has been studied by femtosecond-resolved velocity map imaging of both the CH 3 and I photofragments. The kinetic energy distributions of the two fragments have been recorded as a function of the pump-probe delay, and as a function of excitation within the umbrella and stretching vibrational modes of the CH 3 fragment. These observations are made by using (2+1) Resonant Enhanced MultiPhoton Ionization (REMPI) via the 3p z 2 A 2 " state of CH 3 to detect specific vibrational levels of CH 3 . The vibrational branching fractions of the CH 3 are recovered by using the individual vibrationally state-selected CH 3 distributions to fit the kinetic energy distribution obtained by using nonresonant multiphoton ionization of either the I or CH 3 fragment. The angular distributions and rise times of the two fragments differ significantly. These observations can be rationalized through a consideration of the alignment of the CH 3 fragment and the effect of this alignment on its detection efficiency.Two extra dissociation channels are detected: one associated with Rydberg states near 9.2 eV that were observed previously in photoelectron studies, and one associated with photodissociation of the parent cation around 15 eV.

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Section: Methodsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Time-resolved predissociation of the vibrationless level of the B state of CH3I

Thiré

Cireasa

Staedter

et al. 2011

Phys. Chem. Chem. Phys.

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“…We have examined another class of reactions exhibiting both reactive and nonreactive channels, the collision of halogen atom with alkyl halides (38):…”

Section: Ab ϩ C (Bimolecular)mentioning

confidence: 99%

“…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. For chemical reactions, we used this approach of complexation to study bimolecular reactive (34)(35)(36)(37) and nonreactive (38) scattering, and, by analogy, biomolecular structures exhibiting dative bonding and involved in molecular recognition (39)(40)(41). A descriptive outline of the work over two decades is given in Fig.…”

mentioning

confidence: 99%

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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“…[1][2][3][4][5][6][7][8][9][10][11][12] These assignments were based on the observation of ionized molecular iodine I 2 + as well as direct detection of neutral I 2 . In our recent paper 1 pathways giving rise to I 2 + were investigated.…”

Section: Introductionmentioning

confidence: 99%

Ultraviolet photodissociation of the van der Waals dimer (CH3I)2 revisited. II. Pathways giving rise to neutral molecular iodine

Vidma

Baklanov

Zhang

et al. 2006

The Journal of Chemical Physics

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The formation of neutral I 2 by the photodissociation of the methyl iodide dimer, ͑CH 3 I͒ 2 , excited within the A band at 249.5 nm is evaluated using velocity map imaging. In previous work ͓J. Chem. Phys. 122, 204301 ͑2005͔͒, we showed that the formation of I 2 + from photodissociation of the methyl iodide dimer takes place via ionic channels ͑through the formation of ͑CH 3 I͒ 2 + ͒. It is thus not possible to detect neutral I 2 by monitoring I 2 + . Neutral I 2 is detected in this study by monitoring I atoms arising from the photodissociation of I 2 . Iodine atoms from I 2 photodissociation have a characteristic kinetic energy and angular anisotropy, which is registered using velocity map imaging. We use a two-color probe scheme involving the photodissociation of nascent I 2 at 499 nm, which gives rise to I atoms that are ionized by ͑2+1͒ resonance enhanced multiphoton ionization at 304.67 nm. Our estimate of the yield of nascent I 2 is based on the comparison with the signal from I 2 at a known concentration. Using molecular beams with a small fraction of CH 3 I ͑1% in the expanded mixture͒ where smaller clusters should prevail, the production of I 2 was found to be negligible. An upper estimate for the quantum yield of I 2 from ͑CH 3 I͒ 2 dimers was found to be less than 0.4%. Experiments with a higher fraction of CH 3 I ͑4% in the expanded mixture͒, which favor the formation of larger clusters, revealed an observable formation of I 2 , with an estimated translational temperature of about 820 K. We suggest that this observed I 2 signal arises from the photodissociation of several CH 3 I molecules in the larger cluster by the same UV pulse, followed by recombination of two nascent iodine atoms is responsible for neutral I 2 production.

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Bimolecular reactions observed by femtosecond detachment to aligned transition states: Inelastic and reactive dynamics

Cited by 68 publications

References 66 publications

Time-resolved predissociation of the vibrationless level of the B state of CH3I

Time-resolved predissociation of the vibrationless level of the B state of CH3I

Dynamics of clusters: From elementary to biological structures

Ultraviolet photodissociation of the van der Waals dimer (CH3I)2 revisited. II. Pathways giving rise to neutral molecular iodine

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