O−H Stretch Overtone Excitation in Methyl and Ethyl Hydroperoxides

Homitsky, Sarah C.; Dragulin, Sonia M.; Haynes, Laura M.; Hsieh, Shizuka

doi:10.1021/jp047455l

Cited by 28 publications

(44 citation statements)

References 34 publications

(87 reference statements)

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“…Our measured cross sections for the structured 5 OH band, indicated on the vertical axis of Fig. 2, are in good agreement with the results of Homitsky et al (33), who obtained their values by comparing absorption strengths of CH 3 OOH with known cross sections of overtone transitions in H 2 O, appearing in their photoacoustic spectrum roughly over the same spectral region. The action spectrum in Fig.…”

Section: Resultssupporting

confidence: 91%

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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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Section: Resultssupporting

confidence: 91%

“…The two strong central peaks in the spectrum shown in Fig. 2 agree fairly well with earlier results from the photoacoustic measurements of Homitsky et al (33) Fig. 2.…”

Section: Resultssupporting

confidence: 89%

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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“…Vaghjiani and Ravishankara have studied the photodissociation of MeOOH at wavelengths shorter than 365 nm, 1 and more recently Matthews et al assessed the atmospheric importance of absorption at longer UV wavelengths. 3 Determining absorption cross sections for MeOOH, which are necessary for determining any OH contribution from its direct overtone photolysis, provided the original motivation behind our previous work, 4 and in this work we extend our studies to ab initio calculations of absorption cross sections and to detection of OH radical photodissociation products. 3 Determining absorption cross sections for MeOOH, which are necessary for determining any OH contribution from its direct overtone photolysis, provided the original motivation behind our previous work, 4 and in this work we extend our studies to ab initio calculations of absorption cross sections and to detection of OH radical photodissociation products.…”

Section: Introductionmentioning

confidence: 89%

Effects of torsion on O–H stretch overtone spectra and direct overtone photolysis of methyl hydroperoxide

Haynes

Vogelhuber

Pippen

et al. 2005

The Journal of Chemical Physics

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We use laser photoacoustic spectroscopy to obtain overtone spectra at three through six quanta of O-H stretch excitation (3nu(OH)-6nu(OH)) for methyl hydroperoxide (MeOOH). Extending the spectral regions beyond our previous work reveals new features that can be attributed to transitions involving torsion about the O-O bond. Experimental spectral profiles (3nu(OH)-6nu(OH)) and cross sections (3nu(OH)-5nu(OH)) at room temperature show a good agreement with the simulated spectra that we obtain from ab initio calculations employing a vibration-torsion model at 298 K. A Birge-Sponer analysis yields experimental values for the O-H stretch frequency (omega=3773+/-15 cm(-1)) and anharmonicity (omegax=94+/-3 cm(-1)). We also detect OH radicals by laser-induced fluorescence and present photodissociation action spectra of MeOOH in the regions of 4nu(OH) and 5nu(OH). While the spectral profile at 5nu(OH) mimics the photoacoustic spectrum, the peak intensity for transitions to torsionally excited states is relatively more intense in the action spectrum at 4nu(OH), reflecting the fact that the 4nu(OH) excitation energy is below the literature dissociation energy (D0=42.6+/-1 kcal mol(-1)) so that features in the action spectrum come from thermally populated excited states. Finally, we use our calculations to assign contributions to individual peaks in the room-temperature spectra and relate our findings to a recent dynamics study in the literature.

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“…In the ground electronic state, vibrational overtone excitation may lead to unimolecular reactions through intramolecular vibrational energy redistribution [16][17][18]. Recently, the atmospheric reactions of several O-H containing molecules via direct overtone photodissociation have been studied [19][20][21][22][23][24] and these chromophores have been shown to photoreact. Studying the spectroscopy of a smaller chain perfluorinated carboxylic acid can provide important information about the fate of these compounds in the atmosphere.…”

Section: Introductionmentioning

confidence: 99%

Vibrational spectroscopy of perfluoropropionic acid in the region between 1000 and 11000cm−1

Rontu¹,

Vaida²

2006

Journal of Molecular Spectroscopy

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O−H Stretch Overtone Excitation in Methyl and Ethyl Hydroperoxides

Cited by 28 publications

References 34 publications

The importance of weak absorption features in promoting tropospheric radical production

The importance of weak absorption features in promoting tropospheric radical production

Effects of torsion on O–H stretch overtone spectra and direct overtone photolysis of methyl hydroperoxide

Vibrational spectroscopy of perfluoropropionic acid in the region between 1000 and 11000cm−1

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