Coherent elementary reactions

A new area of research, femtochemistry, in the framework of which reactions are studied in the femtosecond time scale, has recently speared along with the term coherent elementary reactions in which phase characteristics of the motion of atoms in the molecular reacting system are taken into account. 

The term microkinetic analysis has been applied " to attempts to synthesise information from a variety of sources into a coherent reaction model for the hydrogenation of ethene. The input includes steady-state kinetics (most importantly the temperature-dependence of reaction orders ), isotopic tracing, vibrational spectroscopy and TPD it uses deterministic methods, i.e. the solution of ordinary differential equations, for estimating kinetic parameters. It selects a somewhat eclectic set of elementary reactions, and in particular the model... 

The kinetics of the coherent synchronous reactions of HP decomposition and oxidation of pyridine derivatives has been reported. Regioselective oxidation of the pyridine derivatives were studied and conditions have been optimized for the production of 4-vinylpyridine, 4-vinylpyridine oxide, 2,2 -dipyridyl, and pyridine. A probable synchronized reaction mechanism has been suggested for the decomposition of HP and the free radical chain oxidation of pyridine derivatives. It is suggested that the hydroperoxy radical (H02-radical) plays a key role in this reaction mechanism. The activation energy has been calculated for the elementary steps of the dehydrogenation of 4-ethylpyridine. Oxidation of formamidine disulfide with HP in acidic medium results in the formation... 

In a classical Bohr orbit, the electron makes a complete journey in 0.15 fs. In reactions, the chemical transformation involves the separation of nuclei at velocities much slower than that of the electron. For a velocity 105 cm/s and a distance change of 10 8 cm (1 A), the time scale is 100 fs. This is a key concept in the ability of femtochemistry to expose the elementary motions as they actually occur. The classical picture has been verified by quantum calculations. Furthermore, as the deBroglie wavelength is on the atomic scale, we can speak of the coherent motion of a single-molecule trajectory and not of an ensemble-averaged phenomenon. Unlike kinetics, studies of dynamics require such coherence, a concept we have been involved with for some time. 

With the advent of femtosecond lasers, it became possible to observe in real time the actual motion of nuclei and to study the elementary mechanisms pictured by Bodenstein in his description of gas-phase reactions. In all branches of femto-chemistry, this study of elementarity is basic and is due to the inherent resolution achieved in femtochemical studies. Since the velocity of atoms in reactions is 1 km/sec, with 10 fs resolution the distance scale reached is 0,1 A, the atomic scale of motion. As discussed below, this ability to create such localized, coherent wave packets with the atomic scale of distance resolution was part of the development of quantum mechanics as a theoretical construct, but was not an experimental reality until the development of the required time resolution of motion in atoms, molecules, and reactions. 

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