Dissociation of the H2O molecule by collisions with metastable argon (3P2) was shown a few years ago to lead to the excitation of the first vibrational levels of A 2Σ+ excited state of OH. The present work consists of a detailed kinetic study of an e-beam excited Ar–H2O mixture to evaluate the potential interest of that reaction scheme for laser applications. In this study, we have mainly shown that OH* (A 2Σ+) is populated by an Ar++H2O pathway too and we give an estimate for the OH* (A 2Σ+) and OH (X 2Π) formation branching ratios. We have also estimated that Ar*2+H2O is a minor OH* pathway. These results and measurements of main reaction rates permitted us to give a kinetic model where the predicted time dependence of population are in good agreement with the experimental result. The feasibility of a radical laser based on the collisional dissociation scheme of molecules is discussed.
Several new laser effects have been obtained by using electron beam pumped mixtures of a rare gas with another gas. Nevertheless, the laser action in those media appears to be very sensitive to the effect of a transient absorption which can be due to the rare gas itself. Also in this work we have made an experimental study of transient absorptions in the near UV (250–450 nm) for a high pressure of argon excited by relativistic electrons. Two different absorptions have been identified in the present work: (1) A ’’long time’’ absorption attributed to Ar2*(3Σu); the experimental value of its cross section has been found to be in satisfactory agreement with the theoretical one; (2) a ’’short time’’ absorption which exhibits a very broad spectral width, the origin of which is discussed.
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