The photofragmentation of methyl hydroperoxide CH3OOH at 193 and 248 nm in a cold molecular beam

Thelen, Marc; Felder, P.; Huber, J. Robert

doi:10.1016/0009-2614(93)85132-8

Cited by 36 publications

(40 citation statements)

References 22 publications

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“…Vaghjiani and Ravishankara (29) measured the quantum yields for OH production from the photodissociation of CH 3 OOH at 248 nm and showed that it is near unity. This finding was also confirmed under molecular beam conditions by the measurements of Thelen et al (30), who found that at 193 and 248 nm CH 3 O ϩ OH are exclusively produced. The dynamics of the UV photodissocition were further investigated by Novicki and Vasudev (31), who measured vector correlation associated with the OH fragment arising from the dissociation of CH 3 OOH at 266 nm.…”

supporting

confidence: 62%

“…Current tropospheric models include only the photochemistry associated with UV photodissociation of CH 3 OOH between 210 and 360 nm (26). Several laboratory studies (27,28) have shown that CH 3 OOH absorbs strongly over this wavelength region, resulting in excitation to a dissociative electronic excited state and the concomitant production of photofragments (29)(30)(31). Vaghjiani and Ravishankara (29) measured the quantum yields for OH production from the photodissociation of CH 3 OOH at 248 nm and showed that it is near unity.…”

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confidence: 99%

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The importance of weak absorption features in promoting tropospheric radical production

Matthews

Sinha

Francisco

2005

Proc. Natl. Acad. Sci. U.S.A.

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Atmospheric field measurement and modeling studies have long noted discrepancies between observation and predictions of OH and HO 2 concentrations in the atmosphere. Novel photochemical mechanisms have been proposed to explain these differences. Although inclusion of these additional sources improves agreement, they are unable to fully account for the observations. We report and demonstrate the importance of weak electronic absorption features, normally ignored or not measured, in contributing to significant OH radical production. Experiments on methyl hydroperoxide, a prototypical organic peroxide in large abundance in the troposphere, highlights how photochemistry in the neglected electronic absorption tail makes an important addition to the tropospheric OH budget. The present results underscore the need to measure absorption cross sections for atmospheric molecules over a wider dynamic range, especially over the wavelength regions where the solar flux is high, to fully quantitate their contributions to atmospheric photochemistry.absorption cross section ͉ atmospheric photochemistry ͉ electronic absorption ͉ methyl hydroperoxide ͉ photodissociation M ost gases emitted into the atmosphere by natural and anthropogenic activities are removed by their reaction with OH radicals (1-5). Indeed, OH radicals are often called the ''detergent'' of the atmosphere as reaction of trace gases with hydroxyl radicals leads to the oxidation of these volatile compounds and their ultimate removal from the atmosphere (1). Even though it exists in relatively small concentrations, Ϸ10 6 ͞ cm 3 , without the presence of OH radicals the composition of the atmosphere would be vastly different and potentially hazardous as the absence of this radical would lead to a large build-up of toxic atmospheric gases, many of which can also contribute to the greenhouse effect. Hence, accurate modeling of the oxidizing or cleansing capacity of the atmosphere requires knowledge of all significant sources of the hydroxyl radicals. Although several studies have suggested large changes in OH abundances in the atmosphere over the past decades, the direction of the change is apparently unclear. Studies by Krol et al. (6) show a significant global increase in OH, whereas those by Prinn et al. (7) show a decline in OH levels after 1988. Recent studies in the upper troposphere also have reported discrepancies between model predictions and measured HO x (where HO X ϵ OH ϩ HO 2 ) concentrations that strongly depend on solar zenith angles (8-11). These differences between predictions and observation not only highlight the difficulties associated with measuring atmospheric OH concentrations, but also potential variability arising from incomplete accounting of all significant sources and sinks of the OH radical. In this article we present experimental evidence that demonstrates that absorption from oftenneglected weak tails of electronic absorption bands can lead to significant amounts of photochemically generated OH radicals that, apparently, are currently una...

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supporting

confidence: 62%

mentioning

confidence: 99%

The importance of weak absorption features in promoting tropospheric radical production

Matthews

Sinha

Francisco

2005

Proc. Natl. Acad. Sci. U.S.A.

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“…Fifty percent of the photolysis simulations at λ = 300 nm (4.1 eV) resulted in the formation of CH 2 O and H 2 O. Although CH 3 O and OH are the major products of CH 3 OOH gas-phase photolysis (8,(18)(19)(20)(21)(22), the formation of CH 2 O and H 2 O is thermodynamically favored (ΔE = −55 kcal·mol −1 ). However, this process is inhibited by an energy barrier that is ≈3.4 kcal·mol −1 greater than the energy requirement for the formation of CH 3 O and OH in a direct O-O bond cleavage (8).…”

Section: Discussionmentioning

confidence: 99%

“…Fenton-like reactions involving CH 3 OOH and Fe(II) serve as an important source of aqueous HO 2 radicals (16). Finally, recent evidence suggests that reactions between peroxides and isoprene oxidation products lead to the formation of tetrols, thus contributing to the production of secondary organic aerosols (17).It is well established that gas-phase CH 3 OOH photolyzes under UV-visible excitation to form CH 3 O and OH with a quantum yield approaching unity (8,(18)(19)(20)(21)(22)(23). Because of the moderate solubility of CH 3 OOH, it is also likely to undergo condensed-phase photolysis after being taken up by aqueous particles and ice particles and contribute to the production of aqueous free radicals (24).…”

mentioning

confidence: 99%

“…It is well established that gas-phase CH 3 OOH photolyzes under UV-visible excitation to form CH 3 O and OH with a quantum yield approaching unity (8,(18)(19)(20)(21)(22)(23). Because of the moderate solubility of CH 3 OOH, it is also likely to undergo condensed-phase photolysis after being taken up by aqueous particles and ice particles and contribute to the production of aqueous free radicals (24).…”

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Ultrafast photochemistry of methyl hydroperoxide on ice particles

Kamboures

Nizkorodov

Gerber

2010

Proc. Natl. Acad. Sci. U.S.A.

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Simulations show that photodissociation of methyl hydroperoxide, CH 3 OOH, on water clusters produces a surprisingly wide range of products on a subpicosecond time scale, pointing to the possibility of complex photodegradation pathways for organic peroxides on aerosols and water droplets. Dynamics are computed at several excitation energies at 50 K using a semiempirical PM3 potential surface. CH 3 OOH is found to prefer the exterior of the cluster, with the CH 3 O group sticking out and the OH group immersed within the cluster. At atmospherically relevant photodissociation wavelengths the OH and CH 3 O photofragments remain at the surface of the cluster or embedded within it. However, none of the 25 completed trajectories carried out at the atmospherically relevant photodissociation energies led to recombination of OH and CH 3 O to form CH 3 OOH. Within the limited statistics of the available trajectories the predicted yield for the recombination is zero. Instead, various reactions involving the initial fragments and water promptly form a wide range of stable molecular products such as CH 2 O, H 2 O, H 2 , CO, CH 3 OH, and H 2 O 2 .air-water interface | molecular dynamics | peroxides | photodissociation P hotoinduced processes at surfaces of water or ice are of interest in atmospheric chemistry and other areas. However, molecular-level understanding of such processes is largely lacking, because the systems and the interactions involved are complex. In this article, we explore, as a fundamental prototype, the photodissociation of the simplest organoperoxide, CH 3 OOH, on an ice particle. A major motivation for studying this peroxide is its relevance to atmospheric chemistry, as discussed in refs. 1-11 and references therein. Methyl hydroperoxide is typically present in cloud water droplets in micromolar concentrations (7,12,13) and is also likely to occur in aerosols (4,14). The fate of CH 3 OOH in water droplets may influence its role as a reservoir for HO x because this peroxide is known to be a major source of OH at high tropospheric altitudes (10, 15). Fenton-like reactions involving CH 3 OOH and Fe(II) serve as an important source of aqueous HO 2 radicals (16). Finally, recent evidence suggests that reactions between peroxides and isoprene oxidation products lead to the formation of tetrols, thus contributing to the production of secondary organic aerosols (17).It is well established that gas-phase CH 3 OOH photolyzes under UV-visible excitation to form CH 3 O and OH with a quantum yield approaching unity (8,(18)(19)(20)(21)(22)(23). Because of the moderate solubility of CH 3 OOH, it is also likely to undergo condensed-phase photolysis after being taken up by aqueous particles and ice particles and contribute to the production of aqueous free radicals (24). To the best of our knowledge, only two prior experiments examined photolysis of CH 3 OOH in liquid water (9) and ice particles.† Each of these studies identified CH 2 O and H 2 O as major products, suggesting that the photochemistry of CH 3 OOH is conside...

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Photofragment Translational Spectroscopy of Fluorinated Halomethanes

Felder

Yang

Baum

et al. 1994

Israel Journal of Chemistry

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The primary and secondary dissociation processes of CF2Br2 and CF2BrI have been studied by photofragment translational spectroscopy in a pulsed molecular beam. The photolysis of CF2Br2 at 193 nm produces mainly the fragment pair CF2Br + Br and, in a competing primary process, CF2 + Br2. The CF2Br radicals are formed with sufficient internal energy to overcome the barrier of the unimolecular secondary dissociation to CF2+ Br. The photodissociation of CF2BrI at 248 nm also proceeds along two decay pathways involving the fission of the weak C‐I bond and the stronger C‐Br bond, respectively. The former reaction produces spin‐orbit excited iodine atoms I(2P1/2) and stable CF2Br radicals, whereas the latter reaction produces unstable CF2I radicals. The results of this study are compared with those of other workers, and an account of the ultraviolet photochemistry of fluorinated halomethanes is given.

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The photofragmentation of methyl hydroperoxide CH3OOH at 193 and 248 nm in a cold molecular beam

Cited by 36 publications

References 22 publications

The importance of weak absorption features in promoting tropospheric radical production

The importance of weak absorption features in promoting tropospheric radical production

Ultrafast photochemistry of methyl hydroperoxide on ice particles

Photofragment Translational Spectroscopy of Fluorinated Halomethanes

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