Photolysis Of Acetone Research Articles

Direct Measurement of the Rate Constant for the CH2(X̃3B1) + CH3 Reaction at 300 K

The kinetics of the reaction of ground-state methylene radicals (X̃3B1, 3CH2) with methyl radicals (CH3) has been investigated. Both radicals were produced by the photolysis of acetone (CH3C(O)CH3) at 193 nm. Using time-resolved time-of-flight mass spectrometry, the temporal evolution of the concentration of reactants as well as products could be observed simultaneously. Rate coefficients at T = (300 ± 3) K with a bath gas (He) pressure of P = 133 Pa (1 Torr) for 3CH2 + CH3 (1) and CH3 + CH3 (2) have been determined to be: k1 = (2.1 ± 0.7) × 10-10 cm3 molecule-1 s-1 and k2 = (4.6 ± 1.0) × 10-11 cm3 molecule-1 s-1, respectively.

A Measurement of the Yield of Carbon Monoxide from the Reaction of Methyl Radicals and Oxygen Atoms

We have determined the branching fraction for the production of CO from the reaction of methyl radicals and O(3P) atoms at room temperature to be 0.18 ± 0.04 at T = 296 K. The measurement was made by determining the concentration of CO using tunable infrared diode laser absorption. Methyl radicals and O atoms were prepared by 193-nm excimer laser photolysis of acetone and SO2. CO produced directly from acetone photolysis was distinguished from that generated by the radical−radical reaction by using acetone labeled with 13C only on the methyl groups. The result is in excellent agreement with another determination of the CO branching fraction made using time-of-flight mass spectrometry.

Photochemistry of HOx in the upper troposphere at northern midlatitudes

The factors controlling the concentrations of HOx radicals (= OH + peroxy) in the upper troposphere (8–12 km) are examined using concurrent aircraft observations of OH, HO2, H2O2, CH3OOH, and CH2O made during the Subsonic Assessment Ozone and Nitrogen Oxide Experiment (SONEX) at northern midlatitudes in the fall. These observations, complemented by concurrent measurements of O3, H2O, NO, peroxyacetyl nitrate (PAN), HNO3, CH4, CO, acetone, hydrocarbons, actinic fluxes, and aerosols, allow a highly constrained mass balance analysis of HOx and of the larger chemical family HOy (= HOx + 2 H2O2 + 2 CH3OOH + HNO2 + HNO4). Observations of OH and HO2 are successfully simulated to within 40% by a diel steady state model constrained with observed H2O2 and CH3OOH. The model captures 85% of the observed HOx variance, which is driven mainly by the concentrations of NOx (= NO + NO2) and by the strength of the HOx primary sources. Exceptions to the good agreement between modeled and observed HOx are at sunrise and sunset, where the model is too low by factors of 2–5, and inside cirrus clouds, where the model is too high by factors of 1.2–2. Heterogeneous conversion of NO2 to HONO on aerosols (γNO2 = 10−3) during the night followed by photolysis of HONO could explain part of the discrepancy at sunrise. Heterogeneous loss of HO2 on ice crystals (γice_HO2 = 0.025) could explain the discrepancy in cirrus. Primary sources of HOx from O(1D)+H2O and acetone photolysis were of comparable magnitude during SONEX. The dominant sinks of HOy were OH+HO2 (NOx<50 parts per trillion by volume (pptv)) and OH+HNO4 (NOx>50 pptv). Observed H2O2 concentrations are reproduced by model calculations to within 50% if one allows in the model for heterogeneous conversion of HO2 to H2O2 on aerosols (γHO2 = 0.2). Observed CH3OOH concentrations are underestimated by a factor of 2 on average. Observed CH2O concentrations were usually below the 50 pptv detection limit, consistent with model results; however, frequent occurrences of high values in the observations (up to 350 pptv) are not captured by the model. These high values are correlated with high CH3OH and with cirrus clouds. Heterogeneous oxidation of CH3OH to CH2O on aerosols or ice crystals might provide an explanation (γice_CH3OH ∼ 0.01 would be needed).

Kinetic Study of CH3+ HBr and CH3+ Br Reactions by Laser Photolysis−Transient Absorption over 1−100 Bar Pressure Range

Reactions of methyl radicals with hydrogen bromide CH3 + HBr → CH4 + Br (1) and bromine atoms CH3 + Br → CH3Br (2) were studied using excimer laser photolysis−transient UV spectroscopy at 297 ± 3 K over the 1−100 bar buffer gas (He) pressure range. Methyl radicals were produced by 193 nm (ArF) laser photolysis of acetone, (CH3)2CO, and methyl bromide, CH3Br. Temporal profiles of methyl radicals were monitored by UV absorption at 216.51 nm (copper hollow cathode lamp with current boosting). The yield of acetyl radicals in photolysis of acetone at 193 nm was found to be less than 5% at 100 bar He based on the transient absorptions at 222.57 and 224.42 nm. The measured rate constants for reaction 1 are k1 = (2.9 ± 0.7) × 10-12, (3.8 ± 1.5) × 10-12, and (3.4 ± 1.3) × 10-12 cm3 molecule-1 s-1 at the buffer gas (He) pressures of 1.05, 11.2, and 101 bar, respectively. The rate data obtained in this study confirmed high values of the previous (low pressure) measurements and ruled out the possibility of interferen...

Effects of nonmethane hydrocarbons on lower stratospheric and upper tropospheric chemical climatology in a two‐dimensional zonal average model

The effect on the modeled chemical climatology of the upper troposphere and lower stratosphere of including a limited set of nonmethane hydrocarbons in a two‐dimensional (2‐D) zonal average model is presented. Recent measurements of nitrogenated and oxygenated hydrocarbons in the upper troposphere and lower stratosphere have revealed the possibility of significant perturbation of this region. A zonally averaged 2‐D chemical transport model enhanced to represent tropospheric processes was used to explore the extent of this perturbation on global and regional spatial scales and on seasonal and annual average timescales. Acetone was shown to cause a significant increase in the HOx budgets of the upper troposphere in the midlatitude Northern Hemisphere during the winter and early spring months, with acetone photolysis providing the most significant source of HOx radicals. The tropical upper troposphere has a uniform increase in HOx of up to 20% throughout the year because of acetone photolysis. Including the hydrocarbons caused a net increase in ozone of 5 ppbv in the lower and middle troposphere and 5–10 ppbv in the upper troposphere for global and annual averages. The effect of including the hydrocarbons on the calculated model ozone response for the case of doubled surface mixing ratios of atmospheric CH4 is also discussed. It is shown that including hydrocarbons in the model has a significant effect on the modeled ozone response to the methane increase.

Theoretical study on the vibrational state distribution of product CO in the photolysis of acetone $$CH_3 COCH_3 \underrightarrow {hv}2CH_3 + CO$$

The photolysis of acetone has been studied at 6-311G basis set using unrestricted Hartree-Fock method. The results show that ground state acetone (So) cannot easily dissociate. The electrons of acetone undergo n→II transition in laser, and excited acetone (T1) can easily dissociate:\(CH_3 COCH_3 (T_1 )\underrightarrow {hv}CH_3 + CH_3 CO(R_1 )\) and acetyl can further undergo themolytic dissociation: CH3CO→CH3+CO(R2). The dynamic information (ωk B KF V0(S)) of reaction R2 is obtained and the vibrational state distributions of product CO are calculated. The calculated value consists with the experimental value.

Measurements of acetone, acetic acid, and formic acid in the northern midlatitude upper troposphere and lower stratosphere

We have measured acetone, acetic acid, and formic acid concentrations in the upper troposphere and lower stratosphere over Germany. The measurements were performed by ion molecule reaction mass spectrometry using new kinetic data on ion molecule reactions of formic and acetic acids with negative ions obtained at our laboratory. Mean volume mixing ratios between 384 and 832 parts per trillion (pptv) for acetone, 110 and 357 pptv for acetic acid, and 59 and 215 pptv for formic acid were obtained. The correlation between formic acid and acetic acid was very poor (r2 = 0.14). A better correlation could be observed for acetone and acetic acid, with a correlation coefficient r2 = 0.46 and a slope (acetic acid/acetone) of 0.31. For acetic acid a maximum around 9 km was observed. A significant fraction of the acetic acid observed in the lower stratosphere may be due to in situ photochemical production by reactions of HO2 and CH3O2 with peroxy acetyl radicals produced by the photolysis of acetone. In the upper troposphere, vertical transport is much more efficient, and significant acetic acid production is only possible if HOx concentrations are elevated, making the production of acetic acid fast enough to compete with vertical transport.

Sources of HOx and production of ozone in the upper troposphere over the United States

The sources of HOx (OH+peroxy radicals) and the associated production of ozone at 8–12 km over the United States are examined by modeling observations of OH, HO2, NO, and other species during the SUCCESS aircraft campaign in April–May 1996. The HOx concentrations measured in SUCCESS are up to a factor of 3 higher than can be calculated from oxidation of water vapor and photolysis of acetone. The highest discrepancy was seen in the outflow of a convective storm. We show that convective injection of peroxides (CH3OOH and H2O2) and formaldehyde (CH2O) from the boundary layer to the upper troposphere could resolve this discrepancy. More generally, the data collected over the central United States during SUCCESS suggest that local convection was a major source of HOx and NOx to the upper troposphere. The OH and HO2 observations together with the observations of NO allow us to directly calculate the ozone production in the upper troposphere and its dependence on NOx. We find an average net ozone production of 2 ppbv day−1 between 8 and 12 km over the continental United States in the spring. Ozone production was NOx‐limited under essentially all the conditions encountered in SUCCESS. The high levels of HOx present in the upper troposphere stimulate ozone production and increase the sensitivity of ozone to NOx emissions from aircraft and other sources.

OH, HO2, and NO in two biomass burning plumes: Sources of HOx and implications for ozone production

The ER‐2 made two descents through upper tropospheric biomass burning plumes during ASHOE/MAESA. HOx (= OH + HO2) concentrations are largely self‐limited outside the plumes, but become progressively more limited by reactions with NOx (= NO + NO2) at the higher NOx concentrations inside the plumes. Sources of HOx in addition to H2O and CH4 oxidation are required to balance the known HOx sinks both in the plumes and in the background upper troposphere. HOx concentrations were consistently underestimated by a model constrained by observed NOx concentrations. The size of the model underestimate is reduced when acetone photolysis is included. Models which do not include the additional HOx sources required to balance the HOx budget are likely to underestimate ozone production rates.

Observed OH and HO2 in the upper troposphere suggest a major source from convective injection of peroxides

ER‐2 aircraft observations of OH and HO2 concentrations in the upper troposphere during the NASA/STRAT campaign are interpreted using a photochemical model constrained by local observations of O3, H2O, NO, CO, hydrocarbons, albedo and overhead ozone column. We find that the reaction Q(¹D) + H2O is minor compared to acetone photolysis as a primary source of HOx (= OH + peroxy radicals) in the upper troposphere. Calculations using a diel steady state model agree with observed HOx concentrations in the lower stratosphere and, for some flights, in the upper troposphere. However, for other flights in the upper troposphere, the steady state model underestimates observations by a factor of 2 or more. These model underestimates are found to be related to a recent (< 1 week) convective origin of the air. By conducting time‐dependent model calculations along air trajectories determined for the STRAT flights, we show that convective injection of CH3OOH and H2O2 from the boundary layer to the upper troposphere could resolve the discrepancy. These injections of HOx reservoirs cause large HOx increases in the tropical upper troposphere for over a week downwind of the convective activity. We propose that this mechanism provides a major source of HOx in the upper troposphere. Simultaneous measurements of peroxides, formaldehyde and acetone along with OH and HO2 are needed to test our hypothesis.

Temperature and Pressure Dependence of the Multichannel Rate Coefficients for the CH3 + OH System

Laser flash photolysis measurements on the kinetics of the title system in a He bath gas are reported for the temperatures 290, 473, and 700 K and a pressure range of 7.6−678 Torr. CH3 and OH radicals were generated simultaneously by 193 nm photolysis of acetone containing traces of water, with CH3 in large excess. The course of reaction was followed by monitoring the concentration of OH using laser-induced fluorescence (LIF), while CH3 was monitored by absorption at 216.4 nm. The experimental data were analyzed in the first instance by a simple model based on the decay of OH and CH3, which was verified by more comprehensive numerical simulations. Further analysis of the data, using a combined master equation/inverse Laplace transform/RRKM procedure, yielded estimates of the association rate coefficient of CH3 and OH ( = (8.0 ± 0.3) × 10-11 (T/300 K-0.79±0.09 cm3 molecule-1 s-1) and for the enthalpy change for the CH3 + OH → 1CH2 + H2O channel (Δ = 1.6 ± 2.0 kJ mol-1). Pressure-dependent rate coefficients...

Cross-relaxation mechanism for the formation of nuclear polarization: a quantitative time-resolved CIDNP study

The kinetics of the nuclear polarization formed during the photolysis of acetone in isopropanol- d 8 were analyzed quantitatively. Model calculations show that the spin-selective recombination of radicals gives rise to the electron polarization and, with regard to the electron-nuclear cross-relaxation, are adequate to describe the formation of the net nuclear polarization of the reaction products even if the solution contains only one type of radical. For the 2-hydroxy-2-propyl radicals at a magnetic field of 7 T, fitting the theoretical results to the experimental data gives the electron relaxation time T 1 e = 1.0 ± 0.2 μs and the cross-relaxation time T x = 92 ± 18 μs.

Studies of the 193 nm photolysis of diethyl ketone and acetone using time-resolved Fourier transform emission spectroscopy

We have observed the infrared emission from the products of the 193 nm photolysis of diethyl ketone (3-pentanone) in comparison with acetone (2-propanone) using time-resolved Fourier transform spectroscopy. In the photolysis of diethyl ketone, two bands are apparent: The first, spanning the region 1950 to 2250 cm−1, is assigned to CO rovibrational transitions; the other band, spanning the region 2800 to 3400 cm−1 and not exhibiting resolved line structure, is assigned to the ethyl radical. Spectral simulations of the CO bands under conditions of minimal, but not negligible, relaxation produce a lower bound for the nascent CO rotational temperature of ∼2100 K. The CO vibrational population distribution varies slowly over the ∼80 μs time spanned by our experiment. Both the rotational and vibrational energies of CO exceed statistical partitioning in the dissociation of acetone. In comparison to the case of acetone, absolute energies in CO vibration and rotation decrease only modestly for diethyl ketone, corresponding to a dramatic increase in the excess above the statistically partitioned energies. Several simple dissociation models are compared to these results. None is fully satisfactory.

Rotational dependence of the quenching of electronically excited CH(A 2Δ) and CH (B 2Σ −) produced by laser photolysis of acetone at 193 nm

Electronic relaxation rate constants for specific rotational levels of CH(A 2Δ and B 2Σ −) have been measured. In contrast to similar measurements made earlier for other hydrides, the results obtained in the present work show an increase in the quenching efficiency upon rotational excitation. The electronically excited CH states are produced by multiphoton excitation and fragmentation of acetone upon photolysis at 193 nm by means of an ArF excimer laser light. The CG fragments are produced rotationally hot and the time evolution of rotational levels with N′⩽21 for CH(A 2Δ, v′=0) and N′⩽15 for CH(B 2Σ −, v′=0) can be measured.

Molecular decomposition of acetone

The absence of a radical-scavenging effect by [ 2H 4]germane in ArF laser-induced photolysis of acetone at relatively high radiation fluences is consistent with molecular expulsion of ethane from acetone.

Acetone in the atmosphere: Distribution, sources, and sinks

Acetone (CH3COCH3) was found to be the dominant nonmethane organic species present in the atmosphere sampled primarily over eastern Canada (0–6 km, 35°–65°N) during ABLE3B (July to August 1990). A concentration range of 357 to 2310 ppt (= 10−12v/v) with a mean value of 1140±413 ppt was measured. Under extremely clean conditions, generally involving Arctic flows, lowest (background) mixing ratios of 550±100 ppt were present in much of the troposphere studied. Correlations between atmospheric mixing ratios of acetone and select species such as C2H2, CO, C3H8, C2C14and isoprene provided important clues to its possible sources and to the causes of its atmospheric variability. Biomass burning as a source of acetone has been identified for the first time. By using atmospheric data and three‐dimensional photochemical models, a global acetone source of 40–60 Tg (= 1012g)/yr is estimated to be present. Secondary formation from the atmospheric oxidation of precursor hydrocarbons (principally propane, isobutane, and isobutene) provides the single largest source (51%). The remainder is attributable to biomass burning (26%), direct biogenic emissions (21%), and primary anthropogenic emissions (3%). Atmospheric removal of acetone is estimated to be due to photolysis (64%), reaction with OH radicals (24%), and deposition (12%). Model calculations also suggest that acetone photolysis contributed significantly to PAN formation (100–200 ppt) in the middle and upper troposphere of the sampled region and may be important globally. While the source‐sink equation appears to be roughly balanced, much more atmospheric and source data, especially from the southern hemisphere, are needed to reliably quantify the atmospheric budget of acetone.

Internal excitation of methyl radicals produced in the photolysis of acetone at 193 nm and the collisional enhancement of the infrared emission intensity in the .nu.3 spectral region

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTInternal excitation of methyl radicals produced in the photolysis of acetone at 193 nm and the collisional enhancement of the infrared emission intensity in the .nu.3 spectral regionFida Mohammad, Vernon R. Morris, A. Clay Jones, and William M. JacksonCite this: J. Phys. Chem. 1993, 97, 27, 6974–6978Publication Date (Print):July 1, 1993Publication History Published online1 May 2002Published inissue 1 July 1993https://doi.org/10.1021/j100129a009RIGHTS & PERMISSIONSArticle Views48Altmetric-Citations7LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (698 KB) Get e-Alerts

Singlet- and triplet-state photodissociation of CO and CN bonds in aromatic acetones studied by 1H-CIDNP spectroscopy

The photolysis of (4-methoxyphenoxy)acetone ( 1a) and ( N-methylanilino)acetone ( 1b) in fluid solution was investigated by photo 1H chemically induced dynamic nuclear polarization (CIDNP) spectroscopy. The primary step is a dissociation of the CO or CN bond to give acetonyl and 4-methoxyphenoxy or N-methylanilino radicals respectively. For 1a the dissociative state is the singlet state on direct excitation while by triplet state in a separate reaction channel, acetone is formed. On direct excitation, 1b decomposes via both the singlet and the triplet states to the same primary radical pair. At temperatures below 290 K the triplet reaction dominates. With increasing temperature the singlet reaction becomes favoured and thus an unusual inversion of the CIDNP polarization sign is observed. These quite unexpected observations suggest that the photochemistry of these acetone derivatives should not be classified as those of a typical carbonyl compound. Rather, they show strong resemblance to the photo-Claisen reaction of unsatured ethers or the photo-Fries rearrangement of phenyl esters and anilides.

Synthesis of peroxyacetyl nitrate in air by acetone photolysis

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTSynthesis of peroxyacetyl nitrate in air by acetone photolysisPeter Warneck and Thomas ZerbachCite this: Environ. Sci. Technol. 1992, 26, 1, 74–79Publication Date (Print):January 1, 1992Publication History Published online1 May 2002Published inissue 1 January 1992https://doi.org/10.1021/es00025a005RIGHTS & PERMISSIONSArticle Views334Altmetric-Citations41LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (2 MB) Get e-Alerts Get e-Alerts

Wavelength dependence of the primary photodissociation processes in acetone photolysis

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTWavelength dependence of the primary photodissociation processes in acetone photolysisAbraham HorowitzCite this: J. Phys. Chem. 1991, 95, 26, 10816–10823Publication Date (Print):December 1, 1991Publication History Published online1 May 2002Published inissue 1 December 1991https://doi.org/10.1021/j100179a053RIGHTS & PERMISSIONSArticle Views139Altmetric-Citations26LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (973 KB) Get e-Alerts