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On the continuum emissions observed upon oxidation of aluminum and its compounds

1980; Elsevier BV; Volume: 37; Linguagem: Inglês

10.1016/0010-2180(80)90097-8

1556-2921

Steven B. Oblath, James L. Gole,

Atmospheric chemistry and aerosols

The reactions of aluminum with H2O, H2O2, N2O, and O3 have been studied under “single-collision” conditions. We have also examined the reactions of aluminum with moist laboratory air, water, ozone, nitric oxide, and hydrogen peroxide under “multiple-collision” rotationally relaxed conditions. Under multiple-collision conditions, the aluminum-ozone and aluminum-nitric oxide reactions are found to yield resolvable vibronic levels in the spectrum of AlO, whereas reactions with water and moist laboratory air yield a broad emission continuum that must be assigned to a polyatomic emitter. No emission is observed for aluminum oxidation with hydrogen peroxide, this result indicating the unlikely assignment of the continuum emitter to a metal monohydroxide. The combination of single- and multiple-collision studies is used to demonstrate that the continuous emission results from the formation of a metal hydrate. Mechanisms are proposed for this hydration. The current studies are correlated with recent matrix-isolation spectroscopic studies of metal atom-water interactions and theoretical studies of the binding of aluminum-water adducts, both of which corroborate the current analysis. Quenching of the continuous aluminum hydrate emission by H2O, CO2, and O2 has been examined and found to be efficient. It appears that the continuous aluminum hydrate emission may represent a portion of the optical signature of the nighttime and twilight glows observed when trimethyl aluminum is released or aluminum grenades are exploded into the upper atmosphere (90–200 km). This possibility is supported by comparison of upper-atmospheric chemiluminescent intensity distributions observed for the NO + O and aluminum oxidation systems.