Curves excimer dissociation

The purpose of this paper is to present a progress report describing a rather general technique for the study of such electronically excited, dissociative states of simple molecules. We have recently applied this technique to a study of the photolysis of Cs dimers and CsKr excimers in order to resolve two general questions (1) whether relatively broad dissociation bands exist in the spectra that might populate selected product states, and (2) whether such photolytic spectra could lead to useful estimates of the potential curves for the dissociative states involved. 

It is of interest to note that within the limit of acoiracy of these experiments, monomer decay curves (Fig. 22) were single exponential, whereas Sdieme 1 predicts dual exponentiality (Eq. 65). The results thus imply that in pdyslyrene reverse dissociation ( feedback ) of the excimer is not of importance. This point is amplified by time-resolved fluorescence spectra which show that late- ted >ecti a (see experimental section) are composed exclusively of excimer emission (Fig. 23). The same is true in poly(a-methylstyrene) In view of more recent work mi other vinyl aromatic ptdymers, it would be of interest to study pdy(styrene) further with more sophisticated techniques. 

This allows the shapes of the curves in Figs. 35 and 36 to be qualitatively explained. On going from low to high temperature the intensity of the excimer fluorescence first increases because the probability of excimer formation increases faster than the probability of radiationless deactivation. Above a certain temperature dissociation of the excimer becomes predominant and this results in a decrease of the intensity of excimer... 

The rare gas excimer lasers are based on bound-continuum transitions from an excited diatomic species to its dissociative ground state. The observed continuum emission is a superposition of the Franck-Condon factors from the vibrational levels of the upper state. Thus these molecular dissociation lasers display relatively broad fluorescence as a consequence of the steeply repulsive ground-state potential, and there is always a population inversion on such transitions. However, the net gain is significantly lower than that for a bound-bound transition because of the distribution of oscillator strength over the broad fluorescence band. Figure 1 illustrates schematic potential energy curves for such transitions in the excimer and exciplex lasers. 

Figure 13.5 Schematic of potential energy curves for a rare-gas monohalide exciplex laser based on KrF. KrF is formed via two reaction channels. It decays to the ground state via dissociation into Kr and F while emitting a photon at 248 nm. (Adapted with permission from Francis Taylor Group LLC. " ) The diatomic halogen excimer lasers based on F2 also have similar potential energy curves.

TTiese results were explained in Ref. 68 considering the crossings of the incoming Xe + IBr covalent curve with the ionic curves (1), Xe+ + IBr (X 2 +-), and (11), Xe+ + IBr(2ni/2)- The former (outer) crossing will lead to XeBr excimer formation, reaction (32b), because the IBr (X 2 ) ground state dissociates... 

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