Reaction Mechanisms in the Noble Gas Afterglows

Reaction Mechanisms in the Noble Gas Afleisfows.— The above survey of the electronic states of the noble gas molecules allows discussion of the kinetic data accumulated on the pure noble gas afterglows. These data comprise total quenching rate constants for excited atomic states, whidi are summarized in Table 3, and comparisons of the kinetics of atomic emissions with those of the first and second continua, from vdiich attempts have been made to elucidate the mechanisms for the formation of the emitting molecular states. 

For He, two-body removal of He(2 5) and three-body removal of He(2 iS) have been observed. Collisional deactivation of 2 5 to 2 5 (except by electrons ) has been ruled out, so that two-body radiative combination to He2(/4 j ) is probably the dominant mechanism. This has received support from Sando, whose calculations of the intensity of two-body He(2 S) -l- He(l S) emission closely match the observed quenching rate constant. The absence of two-body removal of He(2 iS) by He is consistent with the metastable nature of He2(a S+). As the kinetics of growth of a in the He afterglow match those of the decay of He(2 5), the three-body process can be assigned to recombination into the molecular state.  

For the heavier noble gases there are several complicating factors. Firstly, as yet no separation of the second continue arising from the and 

For Ne, Phelps has compared concentrations as well as decay rates of the atomic states in a pulsed afterglow and has identified the following two-body processes  

Two-body recombination reactions were concluded to be much slower than the above processes. For Ar, Futch and Grant have deduced, from the tonperatuie dependence of the P2 quenching rate constant, that excitation to Pi is no longer dominant, while, for Kr, a definite branching ratio has been obtained, on the basis of the observed rate of deactivation of Pi  

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