The Bromine Afterglow

Of these reactions, (i) has been extensively investigated, and quantitative data are also available " or (ii). Kinetic study of (iii), the bromine afterglow emission spectrum, flrst studied by Gibbs and Ogryzlo, is complicated by appreciable radiation from the B II(0J) state, as well as the A II(lu) state of Brj. Data on the chemiluminescent combination reaction (iv) of two S( P) atoms have also been published. The reactions O -j- O -b M and H -b H -b M do not combine into electronically excited states with allowed transitions to the ground states of O2 and Hs. 

The case of the bromine afterglow emission spectrum is another example of the usefulness of even low resolution spectra in investigating the energy levels of simple molecules. 

Recent work on the weak B-X bands in the bromine afterglow emission spectrum using improved spectral resolution indicates that the prominent transitions arise from vibrational levels, up to v = 9, of the B state of Br2. The energy of two P3/2 bromine atoms at 300 K lies just above = 1 of the B n(0+) excited state. The surprising observation of bands arising from v 9 is due to enhancement of the intensity of emission from these sparsely-populated levels at 300 K by the rapid increase in the Franck-Condon factors with increasing v in this spectral region. ... 

In the bromine afterglow, where emission is observed from levels of the B state above the dissociation limit, such a mechanism might be considered, since no perturbation of rotational energy levels is observed in the absorption spectrum of the B-X system. 

Two different techniques have been used to generate Br atoms and find their concentration. In the first method, Brg, diluted in He, is dissociated in a microwave discharge and the atoms are titrated with NOCl using the bromine afterglow as indicator. In the second method, one first obtains O atoms by dissociation of O2 and monitors their concentration by the familiar titration with NO2. Then a slight excess of Br2 is added to convert the atomic oxygen quantitatively to Br via the rapid reactions ... 

The combination of melamine with hydrated mineral fillers can improve the fire retardancy behavior of PP, eliminating at the same time the afterglow phenomenon associated with these fillers used in isolation.70 Similarly in EVA copolymer, antimony trioxide used in combination with metal hydroxides has been reported to reduce incandescence.56 Chlorinated and brominated flame retardants are sometimes used in combination with metal hydroxides to provide a balance of enhanced fire-retardant efficiency, lower smoke evolution, and lower overall filler levels. For example, in polyolefin wire and cable formulations, magnesium hydroxide in combination with chlorinated additives was reported to show synergism and reduced smoke emission.71... 

Afterglow Kinetics.—Introduction, Combination of atoms in their ground electronic states can lead to the formation of the corresponding diatomic molecule in an electronically excited state. Radiative transitions to a lower-lying state may then lead to chemiluminescent ranission, known as an after ow. Examples include the combination of two nitrogen atoms, a nitrogen atom with an oxygen atom, and two chlorine or bromine atoms ... 

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