Ultraviolet Photolysis of the ClO Dimer

Abstract

Photodissociation of the ClO dimer (ClOOCl) is studied in the ultraviolet regime (250 and 308 nm) under collision-free conditions. The primary photolysis products are probed by photoionization mass spectrometry. At both photolysis wavelengths, exclusively the formation of 2Cl + O 2 is observed, corresponding to a primary quantum yield γ Cl near unity. Considering the error limit of the experimental results one obtains γ Cl g 0.98 at 250 nm and γ Cl g 0.90 at 308 nm, respectively. At both photolysis wavelengths the pathway yielding ClO is not observed, corresponding to γ ClO e 0.02 at 250 nm and γ ClO e 0.10 at 308 nm. Sensitivity studies of these results with respect to ozone depletion in the stratosphere regarding photochemically induced ozone loss are discussed using model simulations. These simulations suggest that a change of γ Cl from 1.0 to 0.9 leads to a reduction of polar ozone loss of ∼5%.

Photoionization of the3s23p43Pand the3s2Barthel1, Flesch2, Rühl3 et al. 2015Phys. Rev. A201200View full textAdd to dashboardCite

“…Plasma radiation is dispersed by a gold coated spherical reflection grating (1200 lines/mm). The absolute number of VUV photons is estimated to be of the order of 10 8 photons per pulse, corresponding to 10 9 photons per second at 10 Hz operation of the lasers, which is similar to previous work [24,25,[42][43][44]. The typical bandwidth of the dispersed VUV photons is set to ∆λ ≈ 2.4 -5.9Å, depending on the spectral features to be resolved in the respective energy regime.…”

Evaluated kinetic and photochemical data for atmospheric chemistry: Volume III – gas phase reactions of inorganic halogens

“…Molina et al (1990) determined φ 2 = 1.03 ± 0.12 at 308 nm using resonance fluorescence detection of Cl. determined φ 2 = 0.9 ± 0.1 and φ 1 = 0.1 ± 0.1 at 248 and 308 nm in a molecular beam experiment, and Plenge et al (2004) determined φ 2 ≥ 0.9 at 308 nm, and φ 1 < 0.02 or φ 1 < 0.1 at 250 and at 308 nm, respectively. These results are also in agreement with the interpretation of the steady-state photolysis experiments of 220 968 275 1376 225 930 280 1136 230 908 285 890 235 883 290 642 240 904 295 435 245 989 300 288 250 1154 305 176 255 1352 310 107 260 1512 315 56 265 1594 320 36 270 1544…”

A re-evaluation of the ClO/Cl&lt;sub&gt;2&lt;/sub&gt;O&lt;sub&gt;2&lt;/sub&gt; equilibrium constant based on stratospheric in-situ observations

“…The temperature dependence implied by n=−2.29 is higher, although it still agrees within its uncertainty given by the fit. Another possible explanation for this effect is the formation of different isomers of Cl 2 O 2 , which has been suggested in numerous theoretical (Fangstrom et al, 1998;Han et al, 1998;Lee et al, 1992;Li and Ng, 1997;McGrath et al, 1990;Stanton et al, 1991;Zhu and Lin, 2003) and experimental (Jacobs et al, 1994;Müller and Willner, 1992;Plenge et al, 2004a;Schwell et al, 1996) studies on the stability of the three stable Cl 2 O 2 isomers, namely chlorine peroxide (ClOOCl), chloryl chloride (ClClO 2 ) and chlorine chlorite (ClOClO). Slanina and Uhlík have presented calculations showing that the relative stabilities of the Cl 2 O 2 isomers and hence the composition of the equilibrium isomeric mixture depends on temperature (Slanina and Uhlik, 1991b), and that this has direct effects on the temperature dependence of K EQ (Slanina, 1992;Slanina and Uhlik, 1991a).…”