Atom-molecule reaction

The standard entropy change for the atom-molecule reactions is in the range 5-20 mole and the halogen molecule dissociation has an eiiU opy change of about 105 e.u. The halogen molecule dissociation energy decreases from chlorine to iodine, but the atom-molecule reactions become more endothermic from chlorine to iodine, and this latter effect probably influences the relative contributions to the mechanism from chain reaction and biinolecular reaction. 

When metal atoms condense on a surface, the recombination to form bulk metal will occur at a rate controlled only by diffusion even at 4 K. Thus, any desired atom-molecule reaction occurring on cocondensation must be very facile to compete with metal polymerization. 

The pressure dependence of the exchange reaction indicates that an atom-molecule reaction or possibly an atom-atom reaction on the surface is the... 

Atom-molecule reactions studied in flow systems the hydrogen halide system... 

Pechukas, P., Light, J.C., and Rankin, C. (1966). Statistical theory of chemical kinetics Application to neutral-atom-molecule reactions, J. Chem. Phys. 44, 794-805. 

Gas-phase reactions of some of the simplest Ge, Sn and Pb compounds have been the subject of a number of investigations. For example, the detailed mechanism responsible for the thermal and photochemical decomposition of germanes, as well as some of the simple radical- and atom-molecule reactions of germanes, have attracted considerable attention in recent years because of the interest in Ge deposition processes. In the case of Sn and Pb compounds, the main interest has been related to environmental problems. 

Within the probable reliability of the data we see that the frequency factors are in good agreement with the theoretical results to be expected for atom-molecule reactions (Table XII.2) and thus provide additional support for the theory. 

E.E. Nikitin, Theory of Elementary Atom-Molecule Reactions. Part 2. Processes. Novosibirsk, Novosibirsk University Press, 1974,220p. (in Russian). 

For a review of the use of hyperspherical harmonics as orbitals in quantum chemistry, (see [97]). Applications to bound state problems have mainly regarded nuclear physics, and are outside the scope of this article. The hyperquantization algorithm had been successfully applied to the prototype ion-molecule reaction He + IlJ HeH+ + H [98,99] and atom-molecule reaction F + H2 HF + H [100,101]. For the latter, resonances were characterized [102,103] and benchmark state-to-state differential cross sections and rate constants [104,105] were given. 

The study of quantum effects such as resonances In atom-molecule reactions has been largely confined to coupled-channel calculations for collisions constrained to colllnear geometries. Progress In quantum reactive scattering techniques Is reviewed periodically (1-4). A few 3D quantum calculations of simple reactions, some more approximate (5-17) than others (18-19), have been concerned with resonance features In the reaction dynamics, and with the Increasing sophistication and sensitivity of molecular beam experiments (20-23), It has become evident that the angular distribution of reaction products Is likely to be the most sensitive observable manifestation of resonant contributions to reaction mechanisms. 

Coupled channel methods for colllnear quantum reactive calculations are sufficiently well developed that calculations can be performed routinely. Unfortunately, colllnear calculations cannot provide any Insight Into the angular distribution of reaction products, because the Impact parameter dependence of reaction probabilities Is undefined. On the other hand, the best approximate 3D methods for atom-molecule reactions are computationally very Intensive, and for this reason. It Is Impractical to use most 3D approximate methods to make a systematic study of the effects of potential surfaces on resonances, and therefore the effects of surfaces on reactive angular distributions. For this reason, we have become Interested In an approximate model of reaction dynamics which was proposed many years ago by Child (24), Connor and Child (25), and Wyatt (26). They proposed the Rotating Linear Model (RLM), which Is In some sense a 3D theory of reactions, because the line upon which reaction occurs Is allowed to tumble freely In space. A full three-dimensional theory would treat motion of the six coordinates (In the center of mass) associated with the two... 

Atom-molecule reactions of hydrogen with COS, ° of carbon with CO, CS, and CS2, of argon with COS, and of barium with C02 have... 

The homogeneous gas phase exchange reactions of diatomic molecules are described by activation energies that are much lower than the decomposition activation energies. The finding is that isotopic equilibrium is reached under reaction conditions in which the contributions from three centre atom—molecule reactions are negligible. 

An atom-molecule reaction of this type has a very minute activation harrier. His analysis indicated that the lifetime of the activated complex formed (K. .. I... CH3) was 10 seconds, shorter than the lifetime of rotation or vibration of the complex. In 1963, Herschhach moved to Harvard and huilt a more sophisticated apparatus. He calculated that a reaction that breaks an ionic bond, rather than a covalent bond, to form an ionic bond should have a longer-lived (more persistent ) activated complex (A, B = alkali metals X = halogen) ... 

G. K. Ivanov and Yu. S. Sayasov, The theory of direct atom-molecule reactions, Part I, Theor. Exp. Chem. 3, 95-101 (1967). 

Fig. 8.5. Reaction cross section, Q E)y for three atom-molecule reactions as a function of collision energy. [Data for K + CH3I reaction from M. E. Gersh and R. B. Bernstein, J. Chem. Phys. 55, 4661 (1971). Data for T + Dg reactions from M. Karplus, R. N. Porter, and R. D. Sharma, J. Chem. Phys. 45, 3871 (1966).]...

Statistical thermodynamics can be used to explain the effect of isotopic substitution on equilibrium constants. Similarly the statistical theory of reaction rates provides a basis for understanding isotope effects in rate constants. Consider a prototype atom-molecule reaction... 

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