Kinetics studies using time-resolved spectroscopy

Time-resolved spectroscopy has become an important field from x-rays to the far-IR. Both IR and Raman spectroscopies have been adapted to time-resolved studies. There have been a large number of studies using time-resolved Raman [39], time-resolved resonance Raman [7] and higher order two-dimensional Raman spectroscopy (which can provide coupling information analogous to two-dimensional NMR studies) [40]. Time-resolved IRhas probed neutrals and ions in solution [41, 42], gas phase kinetics [43] and vibrational dynamics of molecules chemisorbed and physisorbed to surfaces [44]. Since vibrational frequencies are very sensitive to the chemical environment, pump-probe studies with IR probe pulses allow structural changes to... 

Kinetics of the reactions of singlet species 32b in solution at room temperature were studied using time-resolved IR spectroscopy (TRIR) " and nanosecond laser flash photolysis. The absolute rate constants of bimolecular reactions of 32b with... 

Time-Resolved Spectroscopy. Steady-state solvatochromic techniques provide a reasonable means to study solvation processes in supercritical media (5,17-32,43-45,59-68). But, unless the interaction rates between the solute species and the supercritical fluid are slow, these "static" methods cannot be used to study solvation kinetics. Investigation of the kinetics requires an approach that offers inherent temporal resolution. Fortunately, time-resolved fluorescence spectroscopy is ideally suited for this task. 

Grills DC, Huang KW, Muckerman JT, Fujita E. Kinetic studies of the photoinduced formation of transition metal-dinitrogen complexes using time-resolved infrared and UV-visible spectroscopy. Coord Chem Rev 2006 250 1681-95. 

The kinetics of the reaction of NO with methyl radicals in the presence of acetone as the bath-gas was studied by Jodkowski et al,212 using time-resolved infrared absorption spectroscopy. The kinetics of CH3 + NO was studied under pseudo-first-order conditions, i.e. with [NO] [CH3], while the contribution from the self-reaction of methyl radicals... 

Valuable information on the kinetics and mechanism of CF3 + N02 comes from the experimental and theoretical study by Pagsberg et al,226 The experiments, performed using time-resolved infrared diode laser spectroscopy, were supported by ab initio calculations to provide insight into the potential energy surface of the reaction system. The reaction was initiated by pulse radiolysis of Ar/SF6/CF3I mixtures. The abstraction reaction of the iodine atom from CF3I by fluorine atoms leads to the formation of CF3 radicals. The reactions... 

Tran and Fendler have used steady-state and nanosecond time-resolved spectroscopy to study excimer formation for Af-[4-(l-pyrene)butanoyl]-D- and -l-tryptophan methyl esters and their racemate pyr-DL-Trp in methanol and in optically active octanol. Appreciable differences in the kinetics and thermodynamic of excimer formation are observed. 

The technique of representing the intensities of spectral lines as a function of time is referred to as time-resolved spectroscopy. Time resolution of spectroscopic information has been applied to many problems, such as the kinetics of fast decay phosphorus, radiation from fast photolysis sources, and exploding wire phenomena. Of most importance to analytical spectroscopy is the use of time-resolved spectroscopy to study the characteristics of ac spark and ac arc discharges of the type normally used for analytical emission spectral analysis, since such information may be useful in optimizing operating conditions. 

Hydrogen Abstraction Photoexcited ketone intermolecular hydrogen atom abstraction reactions are an interesting area of research becanse of their importance in organic chemistry and dne to the complex reaction mechanisms that may be possible for these kinds of reactions. Time resolved absorption spectroscopy has typically been nsed to follow the kinetics of these reactions but these experiments do not reveal mnch abont the strnctnre of the reactive intermediates. " Time resolved resonance Raman spectroscopy can be used to examine the structure and properties of the reactive intermediates associated with these reactions. Here, we will briefly describe TR experiments reported by Balakrishnan and Umapathy to study hydrogen atom abstraction reactions in the fluoranil/isopropanol system as an example. 

By using PHIP-NMR studies, various intermediates such as the previously elusive dihydrides of neutral and cationic hydrogenation catalysts, as well as hydrogenation product/catalyst complexes, have already been detected during the hydrogenation of styrene derivatives using cationic Rh catalysts. Information about the substituent effect on chemical shifts and kinetic constants has been obtained via time-resolved PASADENA NMR spectroscopy (DYPAS). 

In principle, absorption spectroscopy techniques can be used to characterize radicals. The key issues are the sensitivity of the method, the concentrations of radicals that are produced, and the molar absorptivities of the radicals. High-energy electron beams in pulse radiolysis and ultraviolet-visible (UV-vis) light from lasers can produce relatively high radical concentrations in the 1-10 x 10 M range, and UV-vis spectroscopy is possible with sensitive photomultipliers. A compilation of absorption spectra for radicals contains many examples. Infrared (IR) spectroscopy can be used for select cases, such as carbonyl-containing radicals, but it is less useful than UV-vis spectroscopy. Time-resolved absorption spectroscopy is used for direct kinetic smdies. Dynamic ESR spectroscopy also can be employed for kinetic studies, and this was the most important kinetic method available for reactions... 

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