Comparison of mechanistic model with experimental observation: Part I. The argon(2p(2)) going to argon(1s(4)) emission signal in the pulse radiolysis of argon. Part II. An absorption study of the argon 1s species

In Part I, the temporal behavior of atomic and molecular ions and of several classes of neutral states lying above the Ar(1s) manifold has been mathematically modeled in a successful attempt to reproduce observed Ar(2p{dollar}sb2{dollar})-Ar(1s{dollar}sb4{dollar}) emission signals at 296K with Ar pressures in the 100-200 torr region. In addition, traces of SF{dollar}sb6{dollar} were added to remove the effects of the slow electron thermalization Hornbeck-Molnar cycle characteristic of pure Ar. The proposed model mechanism necessarily includes additional reaction steps introduced by the addition of SF{dollar}sb6{dollar}. Good agreement was obtained between observed and calculated emission profiles only after introduction of Ar{dollar}sbsp{lcub}2{rcub}{lcub}+{rcub}{dollar} as an important thermalizer of fast electrons in pure Ar. Previously published rate constant values for the various elementary steps assumed to comprise a simplest probable mechanism were found to be generally acceptable.; Part II of this work reconciles apparent discrepancies between low and high pressure regimes where earlier workers attempted to fit an AP{dollar}sp2{dollar} + BP parabolic form to Ar(1s) apparent decay constant versus pressure curves. The A parameter, in these earlier works, was equated to an elementary termolecular decay constant for the Ar(1s) species in question and the B parameter was equated to an elementary bimolecular decay constant. However, in the high pressure regime (100-1000 Torr), the A parameter is an order of magnitude smaller and the B parameter is an order of magnitude larger than the low pressure regime (0-50 Torr). The proposed mechanism in this work postulates a reversible termolecular excimer formation step from the correlated Ar(1s) state and multiple reversible vibrational relaxation steps for the excimer. It is then demonstrated analytically that the A and B parameters resulting from a reaction mechanism of this form have no direct mechanistic significance as assumed previously. This proposed mechanism reconciles the discrepancies of the high and low pressure results.