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The kinetics and absolute rate constants of the gas-phase reaction of the hydroxymethyl radical (C[H.sub.2]OH) with molecular oxygen were studied using laser photolysis/near-IR absorption spectroscopy. The results showed slight negative temperature dependence in the measured temperature region.

Thermal decomposition of disilane was investigated using time-of-flight(TOF) mass spectrometry coupled with vacuum ultraviolet single-photon ionization (VUV-SPI) at a temperature range of 675-740 K and total pressure of 20-40 Torr. Comparison between the experimental results and the kinetic simulation results suggested that about 70% of consumed disilane was converted to trisilane, which was observed as one of the main reaction products under the present experimental conditions.

The reactions of C1 atoms with XCH(sub 2)I (X=H, CH(sub 3), C1, Br, I) were studied using cavity ring-down spectroscopy in 25-125 Torr total pressure of N(sub 2) diluent at 250K. Absorption attributable to the formation of the XCH(sub 2)I-C1 adduct following the reaction of C1 atoms with XCH(sub 2)I (X=H, CH(sub 3), C1, Br, I) was measured as a function of temperature over the range 250-320 K.

The absolute absorption spectrum of the benzyl radical in the visible region measured by ring-down spectroscopy in the visible region measured by cavity ring-down spectroscopy is presented. The absorption cross sections reported would facilitate the quantification of the benzyl radical in future kinetic studies.

Cavity ring-down spectroscopy (CRDS) was used to calculate the electronic absorption spectrum of the allyl radical (CH2CHCH2) between 370 and 420 nm at 297 K. In conclusion, the absorption cross-section of the allyl radical at 402.9 nm was determined to be (2.0 plusmn 0.04) x 10(super -19) cm(super 2) molecule(super -1) through study of time-dependent absorption traces.

A deduction of the primary photodissociation mechanism of Si2H6 at 193 nm was made by photoproduct detection by laser-induced fluorescence (LIF) and time-resolved mass spectrometry techniques. Observation of the Si2H6 was conducted by the LIF method. No signal has been detected from SiH3, Si2H5, Si2H3 and Si2H4 in 193 nm photolysis. The importance of H2 elimination processes in Si2H6 produced in 193 nm photolysis was suggested by existing data combination.

A study of the reactions of Cl atoms with RI is conducted using cavity ring-down spectroscopy at a temperature of 233-313 K and at 100 Torr total pressure of N2 diluent. Visible absorption spectra of the RI-Cl adducts are recorded at 440-520 nm at 263 K.

Rate constants relevant to the thermal dissociation of Si(sub 2)H(sub 6) are calculated for the various multichannel unimolecular dissociations and chemical reactions. Quantum chemical calculations indicate that the energies of the saddlepoints for reactions R1 and R2 are lower than the energies of the product state.

Transient absorption spectra and decay profiles of hydroperoxy radical (HO2) are investigated using cw near-IR two-tone frequency modulation absorption spectroscopy at 297 K and 50 Torr in diluent of N2 in the presence of water. The results obtained suggest that the apparent rate of the HO2 self-reaction is enhanced by the formation of the HO2-H2O complex and its subsequent reaction.

The near-ultraviolet absorption spectrum of the phenoxyl radical (C6H5O(super .)) in 10-20 Torr of nitrogen diluent at 298 K is studied using cavity ring-down spectroscopy combined with pulsed laser photolysis. The absorption cross section of the phenoxyl radical was obtained by using a numerical fitting routine on the basis of a modeling of chemical reaction system.

Rate constants for the reactions of Si (3P, 1D, 1S) atoms with SiH4 are obtained using a combined laser photolysis/laser induced fluorescence technique. The results of the density functional theory calculations show that the reaction of Si(3P) atoms with SiH4 proceeds via a loose transition state.

Mid-infrared absorption spectroscopy has been applied to the detection of the hydroperoxyl (HO2) radical in pulsed laser photolysis combined with a laser absorption kinetics reactor. Transitions of the v3 vibrational band assigned to the O-O stretch mode were probed with a thermoelectrically cooled, continuous wave mid-infrared distributed feedback quantum cascade laser (QCL). The HO2 radicals were generated with the photolysis of Cl2/CH3OH/O2 mixtures at 355 nm. The absorption cross section at each pressure was determined by three methods at 1065.203 cm-1 for the F1, 131,13 ← 141,14 transition in the v3 band. From these values, the absolute absorption cross section at zero pressure was estimated. The relative line strengths of other absorptions in the feasible emitting frequency range of the QCL from 1061.17 to 1065.28 cm-1 were also measured, and agreed with values reproduced from the HITRAN database. The v3 band absorption strength was estimated from the analytically obtained absolute absorption cross section and the calculated relative intensity by spectrum simulation, to be 21.4 ± 4.2 km mol-1, which shows an agreement with results of quantum chemical calculations. [ABSTRACT FROM AUTHOR]

Cavity ring-down spectroscopy combined with pulsed laser photolysis has been used to study the near-ultraviolet absorption spectrum (375−410 nm, 2̃2B1 ← X̃2B1 transition) of the phenoxyl radical (C6H5O•) in 10−20 Torr of nitrogen diluent at 298 K. By using a numerical fitting routine on the basis of a modeling of chemical reaction system, the absorption cross section of the phenoxyl radical was obtained, σ = (7.7 ± 2.3) × 10-18 cm2 molecule-1 (base e) at 394.4 nm. A spectrum simulation was carried out using available Franck−Condon integrals with a 400 cm-1 Lorentzian line width, which suggests a short-lived excited state. Time-dependent density functional theory (TD-UB3LYP/aug-cc-pVTZ) calculations supported the interpretation of the absorption band for the phenoxyl radical. The rate constant of the phenoxyl radicals with methyl radicals was derived, k(C6H5O + CH3) = (6.2 ± 2.6) × 10-11 cm3 molecule-1 s-1, at 298 K in 20 Torr of nitrogen diluent. [ABSTRACT FROM AUTHOR]

We report the results of a mass spectrometric study of the effects of atmospherically relevant metal ions on the decomposition of α-hydroxyalkyl-hydroperoxides (α-HHs) derived from ozonolysis of α-terpineol in aqueous solutions. By direct mass spectrometric detection of chloride adducts of α-HHs, we assessed the temporal profiles of α-HHs and other products in the presence of metal ions. In addition, reactions between α-HHs and FeCl 2 in the presence of excess DMSO showed that the amount of hydroxyl radicals formed in a mixture of α-terpineol, O 3 , and FeCl 2 was 5.7 ± 0.8% of the amount formed in a mixture of H 2 O 2 and FeCl 2 . The first-order rate constants for the decay of α-HHs produced by ozonolysis of α-terpineol in the presence of 5 mM acetate buffer at a pH of 5.1 ± 0.1 were determined to be (4.5 ± 0.1) × 10 -4 s -1 (no metal ions), (4.7 ± 0.2) × 10 -4 s -1 (with 0.05 mM Fe 2+ ), (4.7 ± 0.1) × 10 -4 s -1 (with 0.05 mM Zn 2+ ), and (4.8 ± 0.2) × 10 -4 s -1 (with 0.05 mM Cu 2+ ). We propose that in acidic aqueous media, the reaction of α-HHs with Fe 2+ is outcompeted by H + -catalyzed decomposition of α-HHs, which produces the corresponding aldehydes and H 2 O 2 , which can in turn react with Fe 2+ to form hydroxyl radicals.

Ozonolysis of unsaturated organic species with water produces α-hydroxyalkyl-hydroperoxides (α-HHs), which are reactive intermediates that lead to the formation of H 2 O 2 and multifunctionalized species in atmospheric condensed phases. Here, we report temperature-dependent rate coefficients ( k ) for the aqueous-phase decomposition of α-terpineol α-HHs at 283-318 K and terpinen-4-ol α-HHs at 313-328 K. The temporal profiles of α-HH signals, detected as chloride adducts by negative-ion electrospray mass spectrometry, showed single-exponential decay, and the derived first-order k for α-HH decomposition increased as temperature increased, e.g., k (288 K) = (4.7 ± 0.2) × 10 -5 , k (298 K) = (1.5 ± 0.4) × 10 -4 , k (308 K) = (3.4 ± 0.9) × 10 -4 , k (318 K) = (1.0 ± 0.2) × 10 -3 s -1 for α-terpineol α-HHs at pH 6.1. Arrhenius plot analysis yielded activation energies of 17.9 ± 0.7 (pH 6.1) and 17.1 ± 0.2 kcal mol -1 (pH 6.2) for the decomposition of α-terpineol and terpinen-4-ol α-HHs, respectively. Activation energies of 18.6 ± 0.2 and 19.2 ± 0.5 kcal mol -1 were also obtained for the decomposition of α-terpineol α-HHs in acidified water at pH 5.3 and 4.5, respectively. Theoretical kinetic and thermodynamic calculations confirmed that both water-catalyzed and proton-catalyzed mechanisms play important roles in the decomposition of these α-HHs. The relatively strong temperature dependence of k suggests that the lifetime of these α-HHs in aqueous phases (e.g., aqueous aerosols, fog, cloud droplets, wet films) is controlled not only by the water content and pH but also by the temperature of these media.

A detailed inventory was taken of evaporative emissions from parked gasoline vehicles in the Kanto region of Japan, 2015, based on the theoretical model to evaluate the amount of evaporative emissions. The inventory showed that evaporative emissions were high in metropolitan and urban areas because of the large populations in these areas and the high vehicle parking frequency. Using the new inventory, the sensitivity of evaporative emissions to the concentration of tropospheric ozone and secondary organic aerosol was evaluated using the chemical transport modeling solver, the community multiscale air quality modeling system (CMAQ), coupled with the weather research and forecasting (WRF) model. The calculation results showed that the evaporative emissions from permeation through fuel related parts were more significant in the generation of the tropospheric ozone than those from fuel tank venting. This was because the permeation emissions included a high proportion of high maximum incremental reactivity value components, such as aromatics. Neither of the evaporative emission types were significant secondary organic aerosol generators. Whole reduction of the evaporative emissions contributed an approximate 3 ppb decrease in tropospheric ozone in urban areas during the daytime. This information will contribute to the volatile organic compound (VOC) management strategy employed by governments worldwide.

The α-hydroxyalkyl-hydroperoxides [R-(H)C(-OH)(-OOH), α-HH] produced in the ozonolysis of unsaturated organic compounds may contribute to secondary organic aerosol (SOA) aging. α-HHs' inherent instability, however, hampers their detection and a positive assessment of their actual role. Here we report, for the first time, the rates and products of the decomposition of the α-HHs generated in the ozonolysis of atmospherically important monoterpenes α-pinene (α-P), d -limonene ( d -L), γ-terpinene (γ-Tn), and α-terpineol (α-Tp) in water/acetonitrile (W/AN) mixtures. We detect α-HHs and multifunctional decomposition products as chloride adducts by online electrospray ionization mass spectrometry. Experiments involving D 2 O and H 2 18 O, instead of H 2 16 O, and an OH-radical scavenger show that α-HHs decompose into gem -diols + H 2 O 2 rather than free radicals. α-HHs decay mono- or biexponentially depending on molecular structure and solvent composition. e-Fold times, τ 1/e , in water-rich solvent mixtures range from τ 1/e = 15-45 min for monoterpene-derived α-HHs to τ 1/e > 10 3 min for the α-Tp-derived α-HH. All τ 1/e 's dramatically increase in <20% (v/v) water. Decay rates of the α-Tp-derived α-HH in pure water increase at lower pH (2.3 ≤ pH ≤ 3.3). The hydroperoxides detected in day-old SOA samples may reflect their increased stability in water-poor media and/or the slow decomposition of α-HHs from functionalized terpenes.

Acidity changes the physical properties of atmospheric aerosol particles and the mechanisms of reactions that occur therein and on the surface. Here, we used surface-sensitive pneumatic ionization mass spectrometry to investigate the effects of pH on the heterogeneous reactions of aqueous α-terpineol (C 10 H 17 OH), a representative monoterpene alcohol, with gaseous ozone. Rapid (≤10 μs) ozonolysis of α-terpineol produced Criegee intermediates (CIs, zwitterionic/diradical carbonyl oxides) on the surface of water microjets. We studied the effects of microjet bulk pH (1-11) on the formation of functionalized carboxylate and α-hydroxy-hydroperoxide chloride adduct (HH-Cl - ) products generated by isomerization and hydration of α-terpineol CIs, respectively. Compared with the signal at pH ≈ 6, the mass spectral signal of HH-Cl - was less intense under both basic and more acidic conditions, whereas the intensity of the functionalized carboxylate signal increased with increasing pH up to 4 and then remained constant. The decrease of HH-Cl - signals at bulk pH values of >6 is attributable to the accumulation of OH - at the air-water interface that suppresses the relative abundance of hydrophilic HH and Cl - . The present study suggests that α-terpineol in ambient aqueous organic aerosols will be converted into much lower volatile and potentially toxic organic hydroperoxides during the heterogeneous ozonolysis.

Gaseous I2 formation from the heterogeneous reaction of gaseous ozone with aqueous iodide in the presence of aqueous ferrous ion (Fe(2+)) was investigated by electron impact ionization mass spectrometry. Emission of gaseous I2 increased as a function of the aqueous FeCl2 concentration, and the maximum I2 formation with Fe(2+) was about 10 times more than without Fe(2+). This enhancement can be explained by the OH(-) scavenging by Fe(3+) formed from Fe(2+) ozonation to produce colloidal Fe(OH)3. This mechanism was confirmed by measurements of aqueous phase products using a UV-vis spectrometer and an electrospray ionization mass spectrometer. We infer that such a pH-buffering effect may play the key role in general halogen activations.

Mid-infrared absorption spectroscopy has been applied to the detection of the hydroperoxyl (HO(2)) radical in pulsed laser photolysis combined with a laser absorption kinetics reactor. Transitions of the ν(3) vibrational band assigned to the O-O stretch mode were probed with a thermoelectrically cooled, continuous wave mid-infrared distributed feedback quantum cascade laser (QCL). The HO(2) radicals were generated with the photolysis of Cl(2)/CH(3)OH/O(2) mixtures at 355 nm. The absorption cross section at each pressure was determined by three methods at 1065.203 cm(-1) for the F(1), 13(1,13) ← 14(1,14) transition in the ν(3) band. From these values, the absolute absorption cross section at zero pressure was estimated. The relative line strengths of other absorptions in the feasible emitting frequency range of the QCL from 1061.17 to 1065.28 cm(-1) were also measured, and agreed with values reproduced from the HITRAN database. The ν(3) band absorption strength was estimated from the analytically obtained absolute absorption cross section and the calculated relative intensity by spectrum simulation, to be 21.4 ± 4.2 km mol(-1), which shows an agreement with results of quantum chemical calculations.

The reactions of Cl atoms with XCH2I (X = H, CH3, Cl, Br, I) have been studied using cavity ring-down spectroscopy in 25-125 Torr total pressure of N2 diluent at 250 K. Formation of the XCH2I-Cl adduct is the dominant channel in all reactions. The visible absorption spectrum of the XCH2I-Cl adduct was recorded at 405-632 nm. Absorption cross-sections at 435 nm are as follows (in units of 10(-18) cm2 molecule(-1)): 12 for CH3I, 21 for CH3CH2I, 3.7 for CH2ICl, 7.1 for CH2IBr, and 3.7 for CH2I2. Rate constants for the reaction of Cl with CH3I were determined from rise profiles of the CH3I-Cl adduct. k(Cl + CH3I) increases from (0.4 +/- 0.1) x 10(-11) at 25 Torr to (2.0 +/- 0.3) x 10(-11) cm3 molecule(-1) s(-1) at 125 Torr of N2 diluent. There is no discernible reaction of the CH3I-Cl adduct with 5-10 Torr of O2. Evidence for the formation of an adduct following the reaction of Cl atoms with CF3I and CH3Br was sought but not found. Absorption attributable to the formation of the XCH2I-Cl adduct following the reaction of Cl atoms with XCH2I (X = H, CH3, Br, I) was measured as a function of temperature over the range 250-320 K.