Rate Constants for the Recombination of Iodine Atoms in Liquid Hexane and Decane; Temperature Coefficient for the Recombination in Carbon Tetrachloride

Aditya, S.; Willard, John E.

doi:10.1021/ja01568a005

Cited by 19 publications

(10 citation statements)

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“…The rate constant for the nongeminated recombination of I 2 molecules is (3.1±0.5)×10 10 M −1 s −1 . This value is close to that found in CCl 4 solutions by optical spectroscopy 31. Neither the formation of CHI 3 through the nongeminate recombination of CHI 2 and I nor the production of CHI 2 CHI 2 from two CHI 2 radicals were observed.…”

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confidence: 87%

Transient X‐ray Diffraction Reveals Global and Major Reaction Pathways for the Photolysis of Iodoform in Solution

et al. 2008

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The understanding of reaction mechanisms requires detailed information about the processes that take place during the reactions. Various time-resolved optical spectroscopic tools have been developed to track such processes, and reaction dynamics can now be routinely investigated, with a time resolution of tens of femtoseconds, by using these optical techniques. [1][2][3][4][5][6][7][8][9][10][11][12] Typical information provided by timeresolved spectroscopy includes the time constants of reaction intermediates and limited structural information. In most cases, however, detailed structural information, such as the bond lengths and angles in reaction intermediates, are extremely difficult to obtain from time-resolved optical spectroscopy (except for a few favorable cases in which they can be deduced from time-resolved vibrational spectroscopy [4][5][6][7][8][9] and multi-dimensional spectroscopy [10,11] measurements).Replacing the optical probe pulses in time-resolved spectroscopy measurements with either electron [13][14][15][16] or Xray pulses [17][18][19][20][21][22] converts the optical resonances in energy space into atomic interferences in real space, which offers a complementary-and more direct-way to investigate the structural dynamics of molecular reactions. [13][14][15][16][17][18][19][20][21] Because of the relatively low penetration depth of electrons, X-rays are more suitable for probing crystalline [23][24][25] and liquid samples; [17][18][19][20]22] for example, all the atoms in a protein can be tracked during its biological function by means of timeresolved X-ray crystallography, [23][24][25] but to do so it is necessary to produce single protein crystals. This limitation has been recently overcome by introducing transient X-ray liquidography (TXL), a method through which the transient molecular structures present in a liquid sample can be captured in one dimension by performing time-resolved Xray diffraction measurements in the liquid phase. [17][18][19][20][21][22] TXL is a new technique that can be used to investigate reactions in solution, where most of the chemically and biologically relevant processes take place. Since the diffraction patterns generated by the short X-ray pulses arriving at the sample after laser excitation include all the molecular structures present in the irradiated volume, the analysis of TXL data can reveal the structural evolution of all the reaction pathways in the sample (limited only by the signal-to-noise ratio of the diffracted difference signal). We recently succeeded in studying the structural reaction dynamics of several molecules in solution by using this method. [17][18][19][20][21][22] The photochemistry of iodoform (CHI 3 ) has received considerable attention because of the suggested formation of a unique intermediate, called isoiodoform (CHI 2 ÀI), which has been studied by using several time-resolved spectroscopic methods, such as transient absorption and transient resonance Raman spectroscopies. [2,4] According to these studies, a parent iodoform molecule ...

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confidence: 87%

Transient X‐ray Diffraction Reveals Global and Major Reaction Pathways for the Photolysis of Iodoform in Solution

et al. 2008

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“…3A shows the population changes of all related chemical species from the global fitting. HgI and I are the dominant species at 100 ps, and they originate from two-body dissociation, which is essentially completed within a few picoseconds (26,27 (28). HgI 2 forms faster than I 2 , implying that the activation energy for the formation of HgI 2 is lower than that for I 2 .…”

Section: Resultsmentioning

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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“…Although ketones appear to form strong complexes, they have not been studied extensively, possibly because iodination is thought to occur easily. 4 Iodination can usually be avoided or delayed by dilution in an inert solvent, by cooling, and by minimum exposure to light. Infrared studies of acetone and cyclohexanone in solution with iodine have demonstrated that a complex is formed and that the iodine molecule is bound to the keto oxygen.5…”

Section: Introductionmentioning

confidence: 99%

Iodine Complexes with Cyclohexanone and Related Compounds¹

Wobschall¹,

Norton²

1965

J. Am. Chem. Soc.

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Rate Constants for the Recombination of Iodine Atoms in Liquid Hexane and Decane; Temperature Coefficient for the Recombination in Carbon Tetrachloride

Cited by 19 publications

References 1 publication

Transient X‐ray Diffraction Reveals Global and Major Reaction Pathways for the Photolysis of Iodoform in Solution

Transient X‐ray Diffraction Reveals Global and Major Reaction Pathways for the Photolysis of Iodoform in Solution

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

Iodine Complexes with Cyclohexanone and Related Compounds¹

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Rate Constants for the Recombination of Iodine Atoms in Liquid Hexane and Decane; Temperature Coefficient for the Recombination in Carbon Tetrachloride

Cited by 19 publications

References 1 publication

Transient X‐ray Diffraction Reveals Global and Major Reaction Pathways for the Photolysis of Iodoform in Solution

Transient X‐ray Diffraction Reveals Global and Major Reaction Pathways for the Photolysis of Iodoform in Solution

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

Iodine Complexes with Cyclohexanone and Related Compounds1

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Iodine Complexes with Cyclohexanone and Related Compounds¹