IF(A,B) electronic excitation in F+I2F induced by the surface reaction F(ad)+I2(ad)

Wagemann, K.; Chen, X. R.; Wanner, J.
November 1991
Journal of Chemical Physics;11/15/1991, Vol. 95 Issue 10, p7348
Academic Journal
This paper reports on a dynamical study of the reaction of an effusive F atom beam with iodine molecules condensed on a temperature-controlled LiF(001) surface. The observation of IF ground state products by laser-induced fluorescence and of IF(A,B) excited species by visible chemiluminescence can be explained by means of a reaction scheme consisting of two channels. In the first channel IF (X 1Σ+) ground state molecules are formed on the surface and desorb into the gas phase above a threshold temperature of about 200 K, where they are probed by laser-induced fluorescence. The vibrational population ratio [N’(v=0)/N’(v=1)] shows equilibrium of the desorbing molecules with the surface. The population distribution of the IF(v=0) rotational manifold can be well-characterized by a rotational temperature which follows the surface temperature. Surface equilibration of products implies that, unlike in the gas phase reaction F+I2, the products have no memory of their exoergic formation, indicating a Langmuir–Hinshelwood mechanism. In a second reaction channel I2F, as the intermediate in the reaction of fluorine atoms with adsorbed iodine molecules, stabilizes at the surface and desorbs into the gas phase above a surface temperature of 300 K. There it reacts with F atoms according to the chemiluminescence process F+I2F→IF*+IF. This gas phase reaction is identified by the exoergicity limit of the IF (B 3Π) state vibrational population distribution, obtained from analysis of the B→X chemiluminescence. In comparison with Kahler and Lee’s molecular beam synthesis of I2F from I2 and F2 with subsequent secondary encounter with the product F atom, the above reaction scheme represents an alternative induction of the F+I2F reaction. It can explain visible IF chemiluminescence from fluorine–iodine systems under experimental conditions in which F atoms are present and I2 wall adsorption is possible. In this work, evidence...


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