“…The SSA of such an artificially made snow was determined using the VP photochemistry procedure, analogous to our preceding work . This method is based on the comparison of the Norrish type II reaction conversions obtained for different surface loadings under the same irradiation conditions. , When multiple layers of VP molecules are formed, the photoactive molecules in the outermost layer act as an internal optical filter for the remaining molecules, causing a decrease in the overall reaction efficiency. Differently contaminated snow grains (by VP vapors) were thus irradiated, and the reaction conversion was monitored in the melted samples by UV spectroscopy.…”
A combined experimental-computational approach was used to study the self-organization and microenvironment of 1-methylnaphthalene (1MN) deposited on the surface of artificial snow grains from vapors at 238 K. The specific surface area of this snow (1.1 × 10(4) cm(2) g(-1)), produced by spraying very fine droplets of pure water from a nebulizer into liquid nitrogen, was determined using valerophenone photochemistry to estimate the surface coverage by 1MN. Fluorescence spectroscopy at 77 K, in combination with molecular dynamics simulations, and density functional theory (DFT) and second-order coupled cluster (CC2) calculations, provided evidence for the occurrence of ground- and excited-state complexes (excimers) and other associates of 1MN on the snow grains' surface. Only weak excimer fluorescence was observed for a loading of 5 × 10(-6) mol kg(-1), which is ∼2-3 orders of magnitude below monolayer coverage. However, the results indicate that the formation of excimers is favored at higher surface loadings (>5 × 10(-5) mol kg(-1)), albeit still being below monolayer coverage. The calculations of excited states of monomer and associated moieties suggested that a parallel-displaced arrangement is responsible for the excimer emission observed experimentally, although some other associations, such as T-shape dimer structures, which do not provide excimer emission, can still be relatively abundant at this surface concentration. The hydrophobic 1MN molecules, deposited on the ice surface, which is covered by a relatively flexible quasi-liquid layer at 238 K, are then assumed to be capable of dynamic motion resulting in the formation of energetically preferred associations to some extent. The environmental implications of organic compounds' deposition on snow grains and ice are discussed.
“…The SSA of such an artificially made snow was determined using the VP photochemistry procedure, analogous to our preceding work . This method is based on the comparison of the Norrish type II reaction conversions obtained for different surface loadings under the same irradiation conditions. , When multiple layers of VP molecules are formed, the photoactive molecules in the outermost layer act as an internal optical filter for the remaining molecules, causing a decrease in the overall reaction efficiency. Differently contaminated snow grains (by VP vapors) were thus irradiated, and the reaction conversion was monitored in the melted samples by UV spectroscopy.…”
A combined experimental-computational approach was used to study the self-organization and microenvironment of 1-methylnaphthalene (1MN) deposited on the surface of artificial snow grains from vapors at 238 K. The specific surface area of this snow (1.1 × 10(4) cm(2) g(-1)), produced by spraying very fine droplets of pure water from a nebulizer into liquid nitrogen, was determined using valerophenone photochemistry to estimate the surface coverage by 1MN. Fluorescence spectroscopy at 77 K, in combination with molecular dynamics simulations, and density functional theory (DFT) and second-order coupled cluster (CC2) calculations, provided evidence for the occurrence of ground- and excited-state complexes (excimers) and other associates of 1MN on the snow grains' surface. Only weak excimer fluorescence was observed for a loading of 5 × 10(-6) mol kg(-1), which is ∼2-3 orders of magnitude below monolayer coverage. However, the results indicate that the formation of excimers is favored at higher surface loadings (>5 × 10(-5) mol kg(-1)), albeit still being below monolayer coverage. The calculations of excited states of monomer and associated moieties suggested that a parallel-displaced arrangement is responsible for the excimer emission observed experimentally, although some other associations, such as T-shape dimer structures, which do not provide excimer emission, can still be relatively abundant at this surface concentration. The hydrophobic 1MN molecules, deposited on the ice surface, which is covered by a relatively flexible quasi-liquid layer at 238 K, are then assumed to be capable of dynamic motion resulting in the formation of energetically preferred associations to some extent. The environmental implications of organic compounds' deposition on snow grains and ice are discussed.
“…30 It was shown that the kinetics and the product distribution may be altered significantly by medium properties. [31][32][33][34][35][36][37][38][39][40][41] High dielectric and polar solvents affect the relative energies of the 3 nπ* and 3 ππ* excited states. The H-bond interaction between solvent and the solute has a noticeable influence on the subsequent reactions of the biradical intermediate.…”
Section: Jocfeatured Articlementioning
confidence: 99%
“…Because of the conjugation interaction between the aromatic ring and the carbonyl group, aromatic alkyl ketones exhibit some unique photophysical and photochemical properties, which have been the subject of numerous experimental investigations over the past several decades. − It was well-established that the first singlet excited state (S 1 ) lifetime for aromatic ketones (ArCOR) is much shorter than that for aliphatic ketones in the gas and condensed phases. Aromatic carbonyl compounds are highly phosphorescent but only weakly fluorescent.…”
Norrish type reactions for valerophenone in aqueous solution have been investigated by using the combined methods of DFT, CASSCF, and CASPT2 with molecular mechanics. It was found that formation of the intermolecular hydrogen bond in the complex of valerophenone with water results in a blue shift of the n,pi* excited states, while the Coulomb interaction between valerophenone and the bulk surrounding water is mainly responsible for the red shift of the pi,pi* excited states. As a result, the (3)pi pi* state becomes the lowest triplet state and is responsible for the long triplet lifetime observed for aqueous valerophenone. The (1)n pi*, (3)pi pi*, and (3)n pi* states were found to intersect in the same structural region, which appears to be the main reason why the intersystem crossing from (1)n pi* to (3)n pi* is very efficient for aqueous valerophenone and why most aromatic ketones have unique photophysical features such as a short singlet lifetime, high phosphorescence, and weak fluorescence. The Coulomb interaction between valerophenone and the bulk surrounding water has a significant influence on the alpha-C-C cleavage and the 1,5-H shift reaction. The 1,5-H shift is predicted to have a very small barrier on the triplet pathway and the alpha-C-C bond cleavages are not in competition with the 1,5-H shift reaction. This is in good agreement with the experimental findings that Norrish type II quantum yield is close to unity upon photoexcitation of aqueous valerophenone in the wavelength region of 290-330 nm.
“…The values are independent at lower BaP surface loads (sub-monolayer), whereas decreasing values are observed at higher BaP surface loads (above monolayer). The Langmuir concentration = was estimated from the intersection point of two linear least-squares-fits with clearly different slopes 22 , 24 . Figure 2 Determination of Langmuir concentration from kinetic experimental data.…”
Section: Resultsmentioning
confidence: 99%
“…Therefore we termed it approximate specific surface area (ASSA). The ASSA of the soot particles was estimated to be 5 m 2 g −1 , using equation ( 1 ) 23 , 24 : …”
Substantial impacts on climate have been documented for soot‒sulfuric acid (H2SO4) interactions in terms of optical and hygroscopic properties of soot aerosols. However, the influence of H2SO4 on heterogeneous chemistry on soot remains unexplored. Additionally, oxidation rate coefficients for polycyclic aromatic hydrocarbons intrinsic to the atmospheric particles evaluated in laboratory experiments seem to overestimate their degradation in ambient atmosphere, possibly due to matrix effects which are hitherto not mimicked in laboratory experiments. For the first time, our kinetics study reports significant influence of H2SO4 coating on heterogeneous ozonation of benzo(a)pyrene (BaP) deposited on model soot, representative to atmospheric particles. The approximate specific surface area of model soot (5 m2g−1) was estimated as a measure of the availability of surface molecules to a typical gaseous atmospheric oxidant. Heterogeneous bimolecular reaction kinetics and Raman spectroscopy studies suggested plausible reasons for decreased BaP ozonation rate in presence of H2SO4: 1. decreased partitioning of O3 on soot surface and 2. shielding of BaP molecules to gaseous O3 by acid-BaP reaction or O3 oxidation products.
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