Enhanced Organic Nitrate Formation from Peroxy Radicals in the Condensed Phase.

Organic alkoxy (RO) and peroxy (RO) radicals are key intermediates in multiphase atmospheric oxidation chemistry, though most of the study of their chemistry has focused on the gas phase. To better understand how radical chemistry may vary across different phases, we examine the chemistry of a model system, the 1-pentoxy radical, in three phases: the aqueous phase, the condensed organic phase, and the gas phase. In each phase, we generate the 1-pentoxy radical from the photolysis of -pentyl nitrite, run the chemistry under conditions in which RO radicals react with NO, and detect the products in real time using an ammonium chemical ionization mass spectrometer (NH CIMS).

Indoor Air Quality Implications of Germicidal 222 nm Light.

One strategy for mitigating the indoor transmission of airborne pathogens, including the SARS-CoV-2 virus, is irradiation by germicidal UV light (GUV). A particularly promising approach is 222 nm light from KrCl excimer lamps (GUV); this inactivates airborne pathogens and is thought to be relatively safe for human skin and eye exposure. However, the impact of GUV on the composition of indoor air has received little experimental study.

Chemistry of Functionalized Reactive Organic Intermediates in the Earth's Atmosphere: Impact, Challenges, and Progress.

The gas-phase oxidation of organic compounds is an important chemical process in the Earth's atmosphere. It governs oxidant levels and controls the production of key secondary pollutants, and hence has major implications for air quality and climate. Organic oxidation is largely controlled by the chemistry of a few reactive intermediates, namely, alkyl (R) radicals, alkoxy (RO) radicals, peroxy (RO) radicals, and carbonyl oxides (RRCOO), which may undergo a number of unimolecular and bimolecular reactions.

Screening for New Pathways in Atmospheric Oxidation Chemistry with Automated Mechanism Generation.

In the Earth's atmosphere, reactive organic carbon undergoes oxidation via a highly complex, multigeneration process, with implications for air quality and climate. Decades of experimental and theoretical studies, primarily on the reactions of hydrocarbons, have led to a canonical understanding of how gas-phase oxidation of organic compounds takes place. Recent research has brought to light a number of examples where the presence of certain functional groups opens up reaction pathways for key radical intermediates, including alkyl radicals, alkoxy radicals, and peroxy radicals, that are substantially different from traditional oxidation mechanisms.

Experimental and theoretical studies of the doubly substituted methyl-ethyl Criegee intermediate: Infrared action spectroscopy and unimolecular decay to OH radical products.

The infrared (IR) action spectrum of the doubly substituted methyl-ethyl Criegee intermediate (MECI) is observed in the CH stretch overtone region with detection of OH products. The MECI exhibits four conformers, all of which undergo unimolecular decay via a 1,4 H-atom transfer mechanism, followed by the rapid release of OH products. Conformers with different orientations of the carbonyl oxide group with respect to the methyl and ethyl substituents (i.

CH Stretch Activation of CHCHOO: Deep Tunneling to Hydroxyl Radical Products.

Alkene ozonolysis, an important source of hydroxyl (OH) radicals in the Earth's troposphere, proceeds through unimolecular decay of Criegee intermediates. In this work, infrared activation of the methyl-substituted Criegee intermediate, syn-CHCHOO, in the CH stretch fundamental region (2850-3150 cm) is shown to result in unimolecular decay to OH radical products. These excitation energies correspond to only half of the transition state barrier height, and thus the resultant 1,4 H atom transfer that leads to OH products occurs exclusively by quantum mechanical tunneling.

Four-Carbon Criegee Intermediate from Isoprene Ozonolysis: Methyl Vinyl Ketone Oxide Synthesis, Infrared Spectrum, and OH Production.

The reaction of ozone with isoprene, one of the most abundant volatile organic compounds in the atmosphere, produces three distinct carbonyl oxide species (RR'COO) known as Criegee intermediates: formaldehyde oxide (CHOO), methyl vinyl ketone oxide (MVK-OO), and methacrolein oxide (MACR-OO). The nature of the substituents (R,R' = H, CH, CH═CH) and conformations of the Criegee intermediates control their subsequent chemistry in the atmosphere. In particular, unimolecular decay of MVK-OO is predicted to be the major source of hydroxyl radicals (OH) in isoprene ozonolysis.

Selective deuteration illuminates the importance of tunneling in the unimolecular decay of Criegee intermediates to hydroxyl radical products.

Ozonolysis of alkenes, an important nonphotolytic source of hydroxyl (OH) radicals in the atmosphere, proceeds through unimolecular decay of Criegee intermediates. Here, we report a large kinetic isotope effect associated with the rate-limiting hydrogen-transfer step that releases OH radicals for a prototypical Criegee intermediate, CHCHOO. IR excitation of selectively deuterated -CDCHOO is shown to result in deuterium atom transfer and release OD radical products.

Tunneling effects in the unimolecular decay of (CH)COO Criegee intermediates to OH radical products.

Unimolecular decay of the dimethyl substituted Criegee intermediate (CH)COO is observed at energies significantly below the transition state barrier associated with hydrogen atom transfer [Y. Fang et al., J.

Deep tunneling in the unimolecular decay of CHCHOO Criegee intermediates to OH radical products.

Unimolecular decay of Criegee intermediates produced in alkene ozonolysis is known to be a significant source of OH radicals in the troposphere. In this work, unimolecular decay of the methyl-substituted Criegee intermediate, syn-CHCHOO, to OH products is shown to occur at energies significantly below the transition state barrier for a 1,4 hydrogen transfer that leads to these products [Y. Fang et al.

Communication: Real time observation of unimolecular decay of Criegee intermediates to OH radical products.

In the atmosphere, a dominant loss process for carbonyl oxide intermediates produced from alkene ozonolysis is also an important source of hydroxyl radicals. The rate of appearance of OH radicals is revealed through direct time-domain measurements following vibrational activation of prototypical methyl-substituted Criegee intermediates under collision-free conditions. Complementary theoretical calculations predict the unimolecular decay rate for the Criegee intermediates in the vicinity of the barrier for 1,4 hydrogen transfer that leads to OH products.

Jet-cooled fluorescence spectroscopy of a natural product: anethole.

The jet-cooled fluorescence spectroscopy of the natural product molecule anethole ((E)-1-methoxy-4-(1-propenyl)benzene) has been studied. Single vibronic level fluorescence spectroscopy was used to verify the existence of two rotamers, syn and anti, with electronic origins at 32,889 and 32,958 cm(-1), respectively. The excitation and emission spectra show characteristics similar to those of styrene and styrene derivatives, including Cs symmetry and low amplitude motions of the propenyl (vinyl) group.