Reactions of halogen atoms

A considerable wealth of dynamical information has been obtained from studies of halogen atom reactions. The majority of these studies concentrate either on the reactions of fluorine atoms which tend to be faster and more exoergic than the other halogen atom reactions or those reactions which involve the production of a hydrogen halide molecule which may then be studied using infrared chemiluminescence methods. From a chemical point of view, this makes a review of this nature incomplete, but it does reflect the scope of the experimental studies conducted so far. Because of experimental difficulties in reagent preparation, the reduced reactivity and the inability of infrared methods 

F VvY (where X, Y are H or D). This exerts a torque on the newly formed molecule which is greatest when FX is furthest from the centre of mass of XY. Thus the greatest rotational excitation is seen for F + HD - HF + D. 

F + propene F + vinyl chloride F + vinyl bromide F + dichloroethylene F + trichloroethylene F + benzene F + toluene F 4- chlorobenzene F + bromobenzene 

F + toluene F + chlorobenzene F + bromobenzene F + iodobenzene F + dichlorobenzene F + chlorotoluene F + xylene 

Ab initio [515, 516] and semi-empirical calculations [517] of the reaction potential-energy surface show that the potential-energy barrier for reaction depends on the angle of the H—H—F transition state and is lowest for the collinear configuration, having a value 4 kJ mole-1. Thus, collisions involving a nearly collinear approach of F to H2 make the major contribution to reaction and give backward-scattered products. All the surfaces are of a repulsive type. 

Extensive use has been made of classical trajectory methods to investigate various forms of the potential-energy surface for the reaction F + H2. Muckerman [518] has recently presented a very thorough review of potential-energy surfaces and classical trajectory studies for F + H2. The calculations all correctly predict vibrational population inversion, the value of (Fy) and backward scattering of the products. Most calculations overestimate (Fr) and those giving the lowest values of Fr use a potential-energy surface that unrealistically has wells in the entrance and exit valleys [519]. 

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The application of chemiluminescence by Polanyi and his collaborators to the determination of the dissociation energies of sodium and potassium is an elegant but rather specialized study in the field. It was found that when sodium and halogen vapours react in a very dilute flame , intense chemiluminescence is produced, which can only be attributed to the reaction of halogen atoms with Na2 molecules ... 

DIFFERENTIAL CROSS SECTIONS FOR ABSTRACTION REACTIONS OF HALOGEN ATOMS WITH MOLECULAR HYDROGEN INCLUDING NONADIABATIC EFFECTS... 

A. Reactions of Halogen Atoms with Halogen Molecules.283... 

Reactions of Halogen Atoms, Free Radicals, and Excited States... 

Reactions with Ozone. Many reactions of atoms with endothermic compounds, such as ozone, OOO, NCI3, and the azides of chlorine and bromine, have been found to be excellent sources of radicals, often in a state of high vibrational excitation of product. The stratospherically important reactions of halogen atoms and ozone (see Section 5) have recently received wide attention in a number of laboratories. 

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