Low-Pressure Photolysis of 2,3-Pentanedione in Air: Quantum Yields

Article pubs.acs.org/JPCA

Low-Pressure Photolysis of 2,3-Pentanedione in Air: Quantum Yields and Reaction Mechanism Hichem Bouzidi,†,‡ Mokhtar Djehiche,†,‡ Tomasz Gierczak,§ Pranay Morajkar,∥ Christa Fittschen,∥ Patrice Coddeville,†,‡ and Alexandre Tomas*,†,‡ †

Mines Douai, SAGE, 59508 Douai, France Université de Lille, 59000 Lille, France § Faculty of Chemistry, Warsaw University, ul. Pasteura 1, Poland ∥ Université de Lille 1, PC2A, UMR 8522 CNRS/Lille 1, 59655 Villeneuve d’Ascq, France ‡

S Supporting Information *

ABSTRACT: Dicarbonyls in the atmosphere mainly arise from secondary sources as reaction products in the degradation of a large number of volatile organic compounds (VOC). Because of their sensitivity to solar radiation, photodissociation of dicarbonyls can dominate the fate of these VOC and impact the atmospheric radical budget. The photolysis of 2,3-pentanedione (PTD) has been investigated for the first time as a function of pressure in a static reactor equipped with continuous wave cavity ring-down spectroscopy to measure the HO2 radical photostationary concentrations along with stable species. We showed that (i) Stern−Volmer plots are consistent with low OHradical formation yields in RCO + O2 reactions, (ii) the decrease of the photodissociation rate due to pressure increase from 26 to 1000 mbar is of about 30%, (iii) similarly to other dicarbonyls, the Stern−Volmer analysis shows a curvature at the lower pressure investigated, which may be assigned to the existence of excited singlet and triplet PTD states, (iv) PTD photolysis at 66 mbar leads to CO2, CH2O and CO with yields of (1.16 ± 0.04), (0.33 ± 0.02) and (0.070 ± 0.005), respectively, with CH2O yield independent of pressure up to 132 mbar and CO yield in agreement with that obtained at atmospheric pressure by Bouzidi et al. (2014), and (v) the PTD photolysis mechanism remains unchanged between atmospheric pressure and 66 mbar. As a part of this work, the O2 broadening coefficient for the absorption line of HO2 radicals at 6638.21 cm−1 has been determined (γO2 = 0.0289 cm−1 atm−1).

1. INTRODUCTION In the past decade, numerous field studies have encountered strong difficulties in their effort to model the HO x concentration levels observed as much in forested regions1 as in anthropogenic-influenced areas.2 More recently, these findings have been reinforced by total OH reactivity measurement campaigns, where the calculated OH reactivities often underestimate the measured ones.3,4 The chemistry of multifunctional oxygenated volatile organic compounds (VOCs) has been suggested as possibly responsible for the OH missing reactivity and the disagreement in the HOx (OH + HO2) budget.5−7 Dicarbonyls belong to the family of multifunctional VOCs, the main representatives being glyoxal and methyl glyoxal. They are present in the atmosphere at ppt- to ppb- concentration levels, originating mainly from the secondary sources as reaction products in the degradation of several different VOCs. As an example, Grosjean and Grosjean reported the formation of dicarbonyls in alkene ozonolysis reactions following the rearrangement of the Criegee biradical.8 Photochemistry of aromatic compounds is also well-known to generate dicarbonyl compounds, with increasing yields as the degree of ring alkylation increases.9,10 Recently, Crounse et al. proposed a new route for organic compound oxidation in the © 2015 American Chemical Society

atmosphere through the isomerization of peroxy radicals, leading to dicarbonyl species.11 The role of dicarbonyls may be crucial in atmospheric chemistry, especially because they are very sensitive to photolysis in the near-UV range and thus may photodissociate by solar irradiation and directly produce radicals, influencing the oxidative capacity of the atmosphere and the HOx budget. Yet, their gas-phase reactivity is still poorly understood and they are generally not taken into account in atmospheric chemistry models. In addition, although the lifetime of dicarbonyls in the atmosphere is rather short (of the order of a few hours),12 these compounds could reach lower-pressure tropospheric regions; there is thus a need to address also low-pressure photochemistry of dicarbonyls. In this paper, we used the recently developed environmental simulation chamber coupled to in situ continuous wave−cavity ring-down spectrometry (cw-CRDS)13 to study the lowpressure photolysis of 2,3-pentanedione (PTD: CH3C(O)C(O)CH2CH3) as a model compound of α-dicarbonyls. PTD is used as flavoring agent in many perfume and food industries. Ozonolysis of alkenes like 2-ethyl-but-1-ene has also been Received: September 28, 2015 Revised: November 23, 2015 Published: November 26, 2015 12781

DOI: 10.1021/acs.jpca.5b09448 J. Phys. Chem. A 2015, 119, 12781−12789

Article

The Journal of Physical Chemistry A shown to produce PTD.8 PTD has been detected during Indian festivals;14 yet, its atmospheric abundance is not known. Jackson and Yarwood first reported nondissociative emission processes following the UV irradiation of PTD with a total emission quantum yield of 2.2% at 18 mbar and 30 °C.15,16 Szabo et al. investigated the OH radical-initiated oxidation and UV photolysis of PTD at atmospheric pressure and suggested that atmospheric photolysis could be a significant loss process for PTD.17 The predominance of the photolysis channel over the OH radical initiated reaction has been recently confirmed and a photolysis reaction mechanism has been proposed.12 Global primary quantum yields of about 20% were estimated for 2,3-pentanedione and 2,3-hexanedione over the wavelength range 330−470 nm at 1 bar. However, the pressure effect was not evaluated, especially on the quantum yields where it could be significant due to quenching effects. The main aim of this work was to investigate the photolysis of PTD as a function of pressure by determining the product yields of CO, CO2 and CH2O and assessing the chemical mechanism through measurements of the HO2 photostationary concentrations. The present study represents the first lowpressure investigation of 2,3-pentanedione photolysis with direct measurements of both HO2 radicals and stable reactant and products and developing the chemical reaction mechanism.

measurements were only performed in the low pressure part of this work (6.6−105 mbar). CH2O concentration was determined at 6639.33 cm−1. The pressure-dependent absorption cross sections were calculated from the work of Morajkar et al.19 assuming a Voigt profile using a broadening coefficient obtained by Barry et al.20 (air broadening coefficient γ = 1.4 × 10−4 cm−1 Torr−1) and the theoretical Doppler value (νD‑CH2O = 7.44 × 10−3 cm−1). As has been recently reviewed by Ruth et al.,21 several recent publications with different experimental setups18,22−25 consistently indicated that the absorption cross sections reported earlier by Staak et al.26 are ca. a factor of 2 larger than the values measured by Morajkar et al. The absorption cross sections of CO and CO2 were determined in the present work at 66 mbar of air by using calibrated standards and absorption cross sections of 3.19 × 10−22 cm2 (6355.8 cm−1) and 6.38 × 10−22 cm2 (6355.92 cm−1) were found for CO and CO2, respectively. HO2 radicals have been quantified at the strongest absorption line at 6638.21 cm−1. O2 broadening has never been determined for this line, and therefore the O2 broadening of this absorption line has been measured in the frame of this work in independent experiments using laser photolysis coupled to cw-CRDS. Details and results are described further down in the next section. Methanol (99.8%) and PTD (97%) were from Sigma-Aldrich and used as received; Cl2 (10% in N2) was bought from Air Products.

2. EXPERIMENTAL SECTION Experiments have been performed in a quartz photoreactor of cylindrical shape and 116 L volume. A detailed description of the photoreactor could be found in Djehiche et al.13,18 UV lamps emitting in the near UV range (Philips Sylvania, 350− 410 nm, emission spectrum given in Supporting Information Figure S1) surround the reactor and initiated the reactions. Experiment duration lasted from 1 to 3 h. The reactants (either methanol and Cl2 or 2,3-pentanedione) are introduced in the reactor at low pressure (around 1 mbar) followed by addition of synthetic air to reach a total pressure of (6.6−1000) mbar. Initial concentrations of the reactants varied as [CH3OH]0 = (0.67−1.4) × 1015 molecules cm−3, [Cl2]0 = (0.93−2.8) × 1014 molecules cm−3, [PTD]0 = (2.0−3.0) × 1015 molecules cm−3. Because of strong absorption of the OH-scavengers in the near IR region, leading to decrease in the ring-down time and with this a decrease in sensitivity, no OH radical scavenger was used in the PTD photolysis experiments. The first set of experiments employing chlorine photolysis in the presence of methanol aimed at (i) assessing the consistency of the formaldehyde absorption cross sections and (ii) checking the relevance of the present experimental setup to investigate reaction mechanisms of species of atmospheric interest. For these experiments, a chlorine/methanol mixture in air was photolyzed at low pressure and the absorption features of HO2 and CH2O have been determined simultaneously. This wellknown chemical system generates HO2 radicals as the main peroxy radical intermediate and CH2O as the major stable product, both products being quantified by cw-CRDS. In subsequent experiments, both species together with CO and CO2 have been monitored by cw-CRDS during the photolysis of PTD: 2,3-pentanedione was detected and quantified by online mass spectrometry at m/z = 100 Da (Pfeiffer quad-MS) after calibration of the instrument. CH2O, CO, CO2, and HO2 are measured by in situ cwCRDS at 6639.33, 6355.8, 6355.92, and 6638.21 cm−1, respectively. Because line broadening with increasing pressure leads to a decreased sensitivity and selectivity, cw-CRDS

3. RESULTS AND DISCUSSION 3.1. Determination of the O2-Broadening Coefficient for the HO2 Absorption Line at 6638.21 cm−1. The HO2 spectrum has been recorded by Thiébaud et al.27 between 6600 and 6700 cm−1 and exhibits the strongest line at 6638.21 cm−1, twice as big as all other lines and thus very likely being the convolution of two lines. The O2/N2 pressure broadening for several absorption lines of HO2 radicals has been measured,28 however the strongest line, used in this work, was not included at that time. Only recently a pressure broadening of that line29 has been measured in helium. In that experiment, a very weak broadening coefficient (γHe = 3.12*10−5 cm−1 Torr−1) has been obtained combined with a line width extrapolated to zero pressure larger than the theoretical Doppler width (7.088 × 10−3 cm−1 HWHM; represented as a black dot in Figure 2). This result was not unexpected given that the line at 6638.21 cm−1 is probably composed of two nearly perfectly superimposed individual lines. In the frame of this work, we have determined the O2 pressure broadening for this line by determining the line shape at three different O2 pressures (20, 99, and 131 mbar), shown in Figure 1. Laser photolysis coupled to time-resolved cw-CRDS has been employed and details of the experimental setup have been published earlier.30,31 Briefly, HO2 radicals have been generated by 248 nm photolysis of oxalyl chloride, (COCl)2, in the presence of excess CH3OH and O2. Under these conditions, HO2 radicals are rapidly formed and decayed subsequently through self-reaction and diffusion. The two HO2 absorption lines at 6638.21 and 6638.11 cm−1 have been measured with a resolution of 0.002 cm−1 (Figure 1). For this purpose, timeresolved ring-down events have been accumulated over several photolysis pulses until enough ring-down events had occurred to allow a reliable description of the HO2 decay profile at that 12782


Article

The Journal of Physical Chemistry A

agreement with the result obtained for the helium broadening,29 while the broadening coefficient for the weaker line (open squares) equals 8.3 × 10−5 cm−1 Torr−1 and is at the lower end of the earlier published values.28 Using the absolute absorption cross section determined for the line at 6638.21 cm−1 by Thiébaud et al. in 66 mbar of He (2.72 × 10−19 cm2,27), a line strength of S = 7.09 × 10−21 cm−1 can be calculated using the He-broadening coefficient (γHe = 0.024 cm−1/atm) and the zero-pressure line width determined by Morajkar et al.29 (10.72 × 10−3 cm−1 HWHM). Using this line strength as well as the O2-pressure broadening coefficient determined in this work enables calculating the peak absorption cross sections of HO2 in air at the pressures of the experiments for the line at 6638.21 cm−1 (Table 1). Figure 1. Absorption lines at 6638.21 and 6638.11 cm−1 at three different O2 pressures in arbitrary units. The full lines represent the fit to a Voigt profile. Signals have been normalized for each pressure to the surface area of the line at 6638.21 cm−1 such as obtained by the fitting program (HO2 concentrations were not identical for all pressures) and have finally been divided by a constant value so as to reach a maximum value of 1 at the lowest pressure.

Table 1. Pressure Dependent HO2 (6638.21 cm−1) and CH2O (6639.33 cm−1) Absorption Cross Sectionsa

wavelength. Thereafter, the wavelength of the Distributed FeedBack (DFB) laser has been automatically incremented by around 0.002 cm−1 to obtain the time-resolved HO2 profile at the next wavelength. The absorption at time zero after the photolysis pulse is then extracted by fitting the HO2 decay profiles to the second order kinetics and extrapolating to time zero and with this, each time-resolved HO2 decay leads to one data point in Figure 1. More details on the principle of this method can be found in earlier papers.27,32 Measurements have been carried out in pure O2 at three different pressures (20, 99, and 131 mbar). The lines have been fitted to a Voigt profile using the free Fityk software,33 and the obtained line widths (HWHM) for both lines are plotted in Figure 2 as a function of the pressure.

pressure (mbar)

σHO2 (10−19 cm2)

σCH2O (10−22 cm2)

0 6.6 24 66 105

3.24 3.19 3.05 2.74 2.50

4.63 4.24 3.45 2.29 1.70

σHO2 are from the present work while σCH2O are calculated using a line strength of 7.3 × 10−24 cm−1 and an air-broadening coefficient of 1.4 × 10−4 cm−1 Torr−1.19,20. a

3.2. Chlorine/Methanol/Air Mixtures Photolysis. The purpose of these experiments was to assess the consistency of the formaldehyde absorption cross sections and to check the relevance of the present experimental setup to further investigate reaction mechanisms of species of atmospheric interest. Experiments were done at low pressure (6.6−30 mbar) by monitoring CH2O and HO2 absorptions as a function of reaction time. The photolysis of Cl2/CH3OH/air mixtures initiates the oxidation of methanol through CH3OH + Cl reaction followed by the chemical mechanism reported in Table 2. Formaldehyde is the main stable organic product formed in the reaction system while HO2 is the major peroxy radical intermediate. Note that CH2O loss through photolysis was limited to 2% per hour and was thus neglected. As shown by Djehiche et al.,13 the diffusion and loss of HO2 to the reactor walls may be non-negligible at low pressure and has thus been taken into account in the reaction mechanism, based on the recent results of Ivanov et al. 34 The CH 2 O and HO 2 concentrations (noted [X]) were calculated using [X ] =

⎛1 1 1⎞ ⎜ − ⎟ τ0 ⎠ c × σX , P(λ) ⎝ τ

(1)

with c as the speed of light, σX,P(λ) is the absorption cross section of X at pressure P and wavelength λ, and τ and τ0 are the ring-down times at the peak wavelength and at a wavelength just off the absorption peak, respectively. Numerical simulations of the reaction mechanism were performed using CH3OH and Cl2 concentrations as starting conditions and adjusting the Cl2 photolysis frequency to achieve the best agreement with the experimental data. Figure 3 presents typical time profiles of CH2O and HO2 following the irradiation of [CH3OH]0 = 1.4 × 1015 molecules cm−3 and [Cl2]0 = 2.8 × 1014 molecules cm−3 in 24 mbar of air. Both CH2O and HO2 plots displayed very nice agreement between experimental and

Figure 2. Line-width (HWHM) for both lines from Figure 1 as obtained by fitting to a Voigt profile for three pressures.

As it can be seen from Figure 2, the extrapolation to zero pressure for the weaker line (open squares) is in excellent agreement with the expected theoretical Doppler line width (see a black dot), while the extrapolation for the stronger line results in a higher value (10.26 × 10−3 cm−1). The pressure broadening coefficient for the stronger line (open circles) γO2 = 3.8 × 10−5 cm−1 Torr−1 is very small, which is in very good 12783


Article

The Journal of Physical Chemistry A Table 2. Reaction Mechanism Used for the Simulations of the CH2O− and HO2− Experimental Time Profiles chemical reactions

rate coefficients (298 K, 24 mbar air) (cm3 molecule‑1 s‑1)

Cl2 + hν → 2 Cl CH3OH + Cl (+ O2) → HO2 + CH2O + HCl HO2 + HO2 → H2O2 + O2

a 5.5 × 10−11

HO2 + wall → products

0.075b

HO2 + CH2O → HOCH2O2 HOCH2O2 → HO2 + CH2O HO2 + HOCH2O2 → HCOOH + O2 + H2O HO2 + HOCH2O2 → HOCH2O2H + O2 CH2O + Cl (+ O2) → HO2 + CO + HCl Cl + HCOOH (+ O2) → HO2 + HCl + CO2

3.3 × 10−14

1.7 × 10−12

reference this work Atkinson et al, 200635 Atkinson et al, 200436 Ivanov et al., 200734 Morajkar et al., 201323

55b 4.8 × 10−12

Atkinson et al, 200635

7.2 × 10−12 7.3 × 10−11

Figure 4. Experimental and simulated temporal profiles for PTD photolysis. ●, [PTD] (left scale); ▲, [HO2] (right scale); ■, [CH2O] (left scale). The lines correspond to the numerical simulations: solid lines are for conditions 2 (YOH = 0.06) while dotted lines are for conditions 1 (YOH = 0.19). Experimental conditions: [PTD]0 = 2.4 × 1015 molecules cm−3; total pressure = 66 mbar.

1.9 × 10−13

Varies from 3.0 × 10−4 to 8.5 × 10−4 s−1 depending on the number of lamps switched on. bUnits: s−1.

a

CH3C(O)C(O)C2H5 + hν → CH3C(O) + C2H5C(O) (R1)

The corresponding photolysis threshold for R1 is around 400 nm.12,17 At atmospheric pressure, only a small contribution (∼2%) was observed from channel R2 for which the thermodynamic threshold is around 346 nm17 CH3C(O)C(O)C2H5 + hν → CH3C(O) + C2H5 + CO (R2)

OH radicals are formed during the 2,3-pentanedione photolysis in air mostly from RC(O)O2 + HO2 reactions where R = CH3 or C2H5 with branching ratios of ca. 0.4.37,38 It is also well-known that RCO + O2 reaction releases OH radicals from the excited RC(O)O2 adduct at low pressure. Yet, fairly large discrepancies exist in the literature on the OH formation yield: studies of Carr et al. from the Leeds group suggest high OH formation yields for both the CH3CO + O2 and C2H5CO + O2 reactions39−43 while other investigations propose much lower values44−47 including a very recent one48 (see Table 3). No OH-scavenger has been used in these experiments, and therefore the OH-yield will influence the PTD photolysis constant returned by the model calculations (kPTD) through the reaction of OH with PTD: a higher OHyield from reaction RCO + O2 will result in a lower kPTD. Therefore, in order to test the effect of the OH formation yield on the PTD photolysis and CH2O and HO2 kinetic profiles we performed two sets of numerical simulations based on the whole reaction mechanism reported in Table 4: (i) assuming high OH formation yields (conditions 1 see Table 3) and (ii) following the low OH-yield values (conditions 2 see Table 3). Because of absence of data for the C2H5CO + O2 reaction in air and taking into account the only slightly higher values for OHyields obtained in He compared to N2 for CH3CO + O2,40,42,43 we used the same OH formation yields for CH3CO + O2 and C2H5CO + O2 in our simulations. Coproducts of OH in RCO + O2 reactions are assumed to be lactones whose fate is presently unclear; yet, no evidence has been found for lactone decomposition into CO and CH2O

Figure 3. Concentration−time profiles of CH2O (■, right scale) and HO2 (▲, left scale). The lines represent the simulation fits using the reaction mechanism reported in Table 2.

simulated concentrations. Global uncertainties in CH2O and HO2 experimental concentrations, including errors on cross sections and ring-down times τ and τ0, range between 20 and 30%. 3.3. 2,3-Pentanedione Photolysis. Photolysis experiments of 2,3-pentanedione have been carried out between 26 and 1000 mbar of synthetic air to evaluate the pressure effect on the photolysis frequencies and on the yields of the endproducts. Figure 4 presents the obtained PTD, CH2O, and HO2 concentrations versus reaction time for two experiments performed at 66 mbar. PTD absorption spectrum displays two broad bands after 200 nm, one centered at 270 nm, the other at 415 nm.17 With the irradiation system used in the present study, PTD has been shown to fragment mainly into two acyl radicals12 12784


Article


Table 3. OH Radical Yields (YOH) from Carr et al.40 (conditions 1) and Gross et al.44 (conditions 2), PTD Photolysis Constants (kPTD ± 1σ) and PTD Primary Quantum Yields (ΦPTD ± 1σ) Obtained in the Present Work conditions 1 P (mbar)

YOH (%)

26 66 105 132 460 1000

37 19 13 10 3 1

kPTD (h−1) 0.122 0.137 0.133 0.162 0.153 0.142

± ± ± ± ± ±

0.011 0.007 0.011 0.011 0.007 0.007

conditions 2 ΦPTD

YOH (%)

± ± ± ± ± ±

14 6 4 3 1 0

0.17 0.19 0.19 0.23 0.21 0.20

0.02 0.01 0.02 0.02 0.01 0.01

kPTD (h−1) 0.202 0.182 0.176 0.180 0.157 0.140

± ± ± ± ± ±

0.014 0.009 0.011 0.011 0.007 0.007

ΦPTD 0.28 0.26 0.25 0.25 0.22 0.20

± ± ± ± ± ±

0.02 0.02 0.02 0.02 0.02 0.01

Table 4. Chemical Mechanism for 2,3-Pentanedione Photolysis rate constanta

reaction 1 2

CH3C(O)C(O)C2H5 + hν CH3CO + O2

3

C2H5CO + O2

4 5 6 7a 7b 8a 8b 9a 9b 10a 10b 11 12 13a 13b 13c 14a 14b 14c 15 16 17 −17 18 19 20 21 22 23 24 25 26

CH3C(O)O2 + CH3C(O)O2 C2H5C(O)O2 + C2H5C(O)O2 CH3C(O)O2 + C2H5C(O)O2 CH3C(O)O2 + CH3O2 C2H5C(O)O2 + CH3O2 CH3C(O)O2 + C2H5O2 C2H5C(O)O2 + C2H5O2 CH3O + O2 C2H5O + O2 CH3C(O)O2 + HO2

C2H5C(O)O2 + HO2

CH3O2 + HO2 C2H5O2 + HO2 CH2O + HO2 OHCH2O2 OH + CH3C(O)C(O)C2H5 OH + CH2O OH + CH3CHO CH2O + hν HO2 + HO2 + M CH2O + wall PTDO2 + HO2 PTDO2 + CH3C(O)O2 PTDO2 + C2H5C(O)O2

→ → → → → → → → → → → → → → → → → → → → → → → → → → → → → → → → → → → → →

CH3CO + C2H5CO CH3C(O)O2 OH + c-CH2C(O)O C2H5C(O)O2 OH + c-CH2(CH3)C(O)O 2CH3O2 + 2CO2 + O2 2C2H5O2 + 2CO2 + O2 CH3O2 + C2H5O2 + 2CO2 + O2 CH3O2 + CH3O + CO2 + O2 CH3C(O)OH + CH2O + O2 C2H5O2 + CH3O + CO2 + O2 C2H5C(O)OH + CH2O + O2 CH3O2 + C2H5O + CO2 + O2 CH3C(O)OH + CH3CHO + O2 C2H5O2 + C2H5O + CO2 + O2 C2H5C(O)OH + CH3CHO + O2 CH2O + HO2 CH3CHO + HO2 OH + CH3O2 + CO2 CH3C(O)OOH + O2 CH3C(O)OH + O3 OH + C2H5O2 + CO2 C2H5C(O)OOH + O2 C2H5C(O)OH + O3 CH3OOH + O2 C2H5OOH + O2 OHCH2O2 CH2O + HO2 PTDO2 + H2O HO2 + CO + H2O CH3C(O)O2 + H2O H2 + CO H2O2 + O2 + M PTDOOH + O2 CH3O2 + CO2 + CH3CHO + CH3CO C2H5O2 + CO2 + CH3CHO + CH3CO

b 3.3 × 10−12 c 3.3 × 10−12d c 1.5 × 10−11 1.7 × 10−11 1.5 × 10−11d 1.1 × 10−11 α7 = 0.9 1.1 × 10−11d α8 = 0.9b 1 × 10−11 α9 = 0.82 1.2 × 10−11 α10 = 0.82 1.9 × 10−15 1 × 10−14 1.4 × 10−11 α13 = 0.4 β13 = 0.2 1.4 × 10−11 α14 = 0.4d β14 = 0.2 5.2 × 10−12 8 × 10−12 3.3 × 10−14 55e 2.09 × 10−12 8.5 × 10−12 1.5 × 10−11 6 × 10−6e 1.5 × 10−12 2.4 × 10−6e 8 × 10−12d 1.1 × 10−11d,f 1.1 × 10−11d,f

reference Carr et al.40 See text Carr et al.40 See text Sander et al.53 Le Crâne et al.54 Tomas and Lesclaux55 Sander et al.53

Lesclaux56 Le Crâne et al.54 Sander et al.53 Tomas et al.57 Dillon and Crowley38 Tomas et al.57 Le Crâne et al.54 Dillon and Crowley38 Le Crâne et al.54 Sander et al.53 Morajkar et al.23 Szabo et al.17 Sander et al.53 this work Sander et this work Sander et Sander et Sander et

al.53 al.53 al.53 al.53

αi = kia/ki; βi = kic/ki; rate constants in cm3 molecule−1 s−1. bAdjusted to fit the PTD concentrations (varies between 3.7 × 10−5 to 5.1 × 10−5 s−1). See Table 3. dRate constants unavailable in the literature, which were replaced by the rate constants of the corresponding acetyl- or methyl-peroxy radicals reactions. C2H5O2 was used as analogue for PTDO2. eIn s−1. fThe PTDO radical (CH3C(O)C(O)CH(O)CH3) is supposed to decompose instantaneously into CH3CHO and CH3CO. a c

PTD photolysis constants were thus retrieved from numerical simulations undertaken for conditions 1 and 2. For conditions 1, kPTD varies between (0.122 ± 0.011) and (0.162 ± 0.011) h−1 in the pressure range 26−1000 mbar; for conditions 2, kPTD decreases from (0.202 ± 0.009) h−1 at 26 mbar to (0.140 ± 0.007) h−1 at 1000 mbar (see Table 3). The

(respectively CO and CH3CHO) in CH3CO + O2 (respectively C2H5CO + O2).43,45,49 Numerical simulation input data included only the initial PTD concentration; the photolysis constant kPTD was the only parameter adjusted to fit the PTD concentrations and to find the best agreement between modeled and experimental PTD concentrations. 12785


Article

The Journal of Physical Chemistry A uncertainties on kPTD reflect the error (1σ) on the simulation fit of [PTD] versus time. Aiming at determining PTD primary quantum yields (ΦPTD) as a function of pressure, NO2 was selected as actinometer and its photolysis constant (kNO2) was retrieved in the same experimental conditions as PTD using the method developed by Holmes et al.50 An NO2 photolysis rate of (9.8 ± 0.5) h−1 was determined, independent of pressure. Using the known PTD and NO2 UV absorption cross calc sections17,36 the photolysis rate constant ratio of kcalc PTD/kNO2 was calculated according the following equation kicalc =

∫λ Φi(λ)σi(λ)F(λ)dλ

yields for PTD photolysis obtained under conditions 1 and 2 is striking; whereas no clear pressure effect is visible for high OH yield conditions (conditions 1), a measurable effect is observed for low OH yield conditions (conditions 2). As observed for other carbonyls irradiated at wavelengths near 400 nm,52 a nonlinear SV behavior is observed in Figure 5 for conditions 2 with a large slope for the lower part of the pressure range investigated and a strong reduction at high pressures. This behavior has been assigned to the existence of two excited PTD states (singlet and triplet) from which photodissociation occurred, though internal conversion and ro-vibrational relaxation from the singlet state may also be invoked. Because of the relatively narrow emission band of the lamps interacting with only the near-UV broad PTD absorption band, it is expected that only one electronic singlet state is concerned in the photochemical process. Therefore, we concluded that OH formation from RCO + O2 reactions most likely follows data obtained by Gross et al.44 and recently by Papadimitriou et al.48 The zero pressure value (corresponding to the intercept of the SV plot) is difficult to extract from the present data. Jackson and Yarwood reported nondissociative emission processes (fluorescence and phosphorescence) following the UV irradiation of PTD.15,16 Total emission (mainly phosphorescence) quantum yields of only 0.022 at 18 mbar and 30 °C upon excitation at 405 and 436 nm were obtained, dropping to 0.011 at 365 nm.15,16 A pressure-dependent glyoxal photolysis study at long wavelengths indicated the existence of multiple states,52 which may be also the case for PTD, explaining the curved SV plot obtained. To the best of our knowledge, this is the first study of pressure effect on the photodissociation kinetics of 2,3-pentanedione. Three reaction products CO2, CH2O, and CO have been detected and quantified by cw-CRDS for the experiments carried out at 66 mbar. CH2O was also quantified in the experiments at 105 and 132 mbar. Product yields were obtained by plotting the product concentration versus [PTD]reacted, where [PTD]reacted represents the difference between initial [PTD] and [PTD] at time t. CH2O concentrations have been corrected for wall loss and photolysis, representing a loss of about 15% CH2O at the end of the experiment. As shown in Figure 6, CO2, CH2O, and CO plots are linear giving yields of 1.16 ± 0.04, 0.33 ± 0.02, and 0.070 ± 0.005, respectively. No pressure effect on the CH2O yield has been observed between 66 and 132 mbar. Note that these yields do not correspond exactly to the PTD photolysis yields, as the unscavenged OH radicals reacting with PTD may also in consequence produce CO2, CH2O, and CO. Quoted uncertainties represent precision on the linear regression fits. Systematic errors can arise from uncertainties in CO2, CH2O, and CO absorption cross sections and in PTD concentrations. Using the propagation of errors enabled estimating global uncertainties of 20, 29, and 33% on CO2, CO, and CH2O yields, respectively. The CO yield obtained at 66 mbar (0.070) is in excellent agreement with that resulting from the numerical simulations (0.065) and with that obtained by Bouzidi et al. at 1 bar in the absence of OH radical scavenger (0.076).12 One of the main sources of CO is probably the photolysis of formaldehyde. In the case of CH2O, the yield (0.33) determined from experiments at 66, 105, and 132 mbar is somewhat lower than that obtained at 1 bar (0.41).12 This may be due to the additional CH2O loss by reaction with OH radicals coming from RCO + O2 at low pressure, as exemplified by the lower CH2O yield obtained by Bouzidi et al. at 1 bar when the OH

(2)

F(λ) represents the relative actinic flux intensity and was recorded using a spectroradiometer (SolaTell, spectral resolution of 0.5 nm). σi(λ) represent the wavelengthdependent absorption cross sections of PTD or NO217,36 and Φi(λ) represent the PTD or NO2 quantum yields. PTD photolysis quantum yield was set to unity and ΦNO2(λ) were from Atkinson et al.36 Then, ΦPTD were calculated as a function of total pressure for conditions 1 and 2 according to the following equation12,51 ΦPTD =

kPTD k NO2 calc kPTD calc k NO 2

(3)

The quantum yield data are summarized in Table 3 for all experiments carried out at total pressures of 26, 66, 105, 132, 460, and 1000 mbar and are shown in the form of Stern− Volmer (SV) plots in Figure 5. Displayed uncertainties (±1σ) are calculated using the error propagation method and took into account estimated uncertainties on kPTD and kNO2. The primary quantum yield obtained at 1 bar of 0.20 is in excellent agreement with that of 0.19 reported by Bouzidi et al.12 from a Teflon smog chamber study. The difference between quantum

Figure 5. Stern−Volmer plot for 2,3-pentanedione photolysis between 350 and 410 nm reporting the reciprocal of the primary quantum yield as a function of total pressure. □: ΦPTD are calculated from simulations under conditions 1 (high OH yield values). △: ΦPTD are calculated from simulations under conditions 2 (low OH yield values); the values are fitted to a log-normal law. Error bars represent 1σ. 12786


Article


It can be concluded that photolysis is by far the major degradation pathway of 2,3-pentanedione. Finally, the time-resolved measurement of HO2 photostationary concentrations using cw-CRDS and combined with the reaction mechanism modeling has allowed assessing the photolysis reaction mechanism of 2,3-pentanedione and demonstrates the interest of measuring both radicals and stable compounds in atmospheric simulation experiments.58

■

ASSOCIATED CONTENT

S Supporting Information *

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.jpca.5b09448. PTD and NO2 absorption spectra as well as the lamp emission spectrum are given in Figure S1. (PDF)

■

AUTHOR INFORMATION

Corresponding Author

Figure 6. Product yield plots of CO2 (●, 66 mbar), CH2O (*, 66 mbar, ▼, 105 mbar, ▲, 132 mbar), and CO (⧫, 66 mbar). The CO concentrations have been multiplied by 2 for clarity. The lines correspond to linear regression fits on the values at 66 mbar.

*E-mail: [email protected]. Tel.: 00.33.3.27.71.26.51. Fax: 00.33.3.27.71.29.14. Present Addresses

(M.D.) University M’Sila, Faculty of Sciences, M’Sila, Algeria. (P.M.) Goa University, Department of Chemistry, Taleigao 403206, Goa, India.

radicals were not scavenged. Carbon dioxide mainly comes from the rapid decomposition of acyloxy RC(O)O radicals produced in the reactions of acylperoxy radicals, RC(O)O2, with alkyl- and acyl-peroxy radicals. In addition to stable products, HO2 photostationary concentrations were also recorded, starting with levels of ∼4 × 1010 radical cm−3, and slightly decreasing with reaction time (about 5−10%). Using the same methodology as Bouzidi et al. to simulate the reaction mechanism displayed in Table 4 CH2O and HO2 radical concentrations were simulated and compared to the measured ones (Figure 4). Overall, the better agreement appears for simulations performed using low OH formation yields, especially on HO2 concentrations, as illustrated by Figure 4. This confirms the results obtained by Stern−Volmer analysis and also indicates that the reaction mechanism used for the numerical simulations is satisfactory in terms of chemical reactions used and rate coefficients associated with them.

Notes

The authors declare no competing financial interest.

■

ACKNOWLEDGMENTS The present work takes place in the Labex CaPPA (Chemical and Physical Properties of the Atmosphere) funded by the French National Research Agency (ANR) through the PIA (Programme d’Investissements d’Avenir) under contract ANR11-LABX-005-01 and by the Regional Council “Nord-Pas de Calais” and the European Funds for Regional Economic Development (FEDER). It is also supported by the Lefe-Chat program from INSU-CNRS. IRENI program is also acknowledged for financial support. H.B. is grateful for a Ph.D. scholarship from the Nord-Pas de Calais Regional Council and Mines Douai. T.G. is grateful for a 1 month invited-professor Grant at Mines Douai. The authors are grateful to D. Petitprez from PC2A for lending the mass spectrometer.

4. CONCLUSIONS The photolysis of 2,3-pentanedione (between 350 and 410 nm) has been investigated for the first time as a function of pressure in a static reactor equipped with cw-CRDS. As at atmospheric pressure, the low-pressure photolysis mechanism initially proceeds by the carbonyl−carbonyl bond scission. Analysis of the pressure effect on PTD photolysis primary quantum yields using Stern−Volmer analysis as well as CH2O and HO2 time profile numerical simulations revealed inconsistencies when using high OH formation yields from RCO + O2 reactions. Thus, the present work clearly favors low OH formation yields determined by several groups. The photolysis rate of PTD has been shown to be only slightly pressure-dependent with quantum yields increasing from 0.20 to more than 0.28 from atmospheric to zero pressure and between 350 and 410 nm. The estimated photodecomposition lifetime of PTD is about 1 h in the low troposphere and somewhat shorter at higher altitudes. Compared to the lifetime due to the reaction with OH radicals, PTD atmospheric lifetime is of the order of 5 days (for an atmospheric OH concentration of ca. 1 × 106 molecules cm−3).

■

REFERENCES

(1) Lelieveld, J.; Butler, T. M.; Crowley, J. N.; Dillon, T. J.; Fischer, H.; Ganzeveld, L.; Harder, H.; Lawrence, M. G.; Martinez, M.; Taraborrelli, D.; et al. Atmospheric oxidation capacity sustained by a tropical forest. Nature 2008, 452, 737−740. (2) Hofzumahaus, A.; Rohrer, F.; Lu, K.; Bohn, B.; Brauers, T.; Chang, C.-C.; Fuchs, H.; Holland, F.; Kita, K.; Kondo, Y.; et al. Amplified trace gas removal in the troposphere. Science 2009, 324, 1702−1704. (3) Nölscher, A. C.; Williams, J.; Sinha, V.; Custer, T.; Song, W.; Johnson, A. M.; Axinte, R.; Bozem, H.; Fischer, H.; Pouvesle, N.; et al. Summertime total OH reactivity measurements from boreal forest during HUMPPA-COPEC 2010. Atmos. Chem. Phys. 2012, 12, 8257− 8270. (4) Dolgorouky, C.; Gros, V.; Sarda-Esteve, R.; Sinha, V.; Williams, J.; Marchand, N.; Sauvage, S.; Poulain, L.; Sciare, J.; Bonsang, B. Total OH reactivity measurements in Paris during the 2010 MEGAPOLI winter campaign. Atmos. Chem. Phys. 2012, 12, 9593−9612. (5) Hens, K.; Novelli, A.; Martinez, M.; Auld, J.; Axinte, R.; Bohn, B.; Fischer, H.; Keronen, P.; Kubistin, D.; Nölscher, A. C.; et al.

12787


Article

The Journal of Physical Chemistry A Observation and modelling of HOx radicals in a boreal forest. Atmos. Chem. Phys. 2013, 14, 8723−8747. (6) Nakashima, Y.; Kato, S.; Greenberg, J.; Harley, P.; Karl, T.; Turnipseed, A.; Apel, E.; Guenther, A.; Smith, J.; Kajii, Y. Total OH reactivity measurements in ambient air in a southern Rocky mountain ponderosa pine forest during BEACHON-SRM08 summer campaign. Atmos. Environ. 2014, 85, 1−8. (7) Lou, S.; Holland, F.; Rohrer, F.; Lu, K.; Bohn, B.; Brauers, T.; Chang, C. C.; Fuchs, H.; Häseler, R.; Kita, K.; et al. Atmospheric OH reactivities in the Pearl River Delta − China in summer 2006: measurement and model results. Atmos. Chem. Phys. 2010, 10, 11243− 11260. (8) Grosjean, E.; Grosjean, D. The gas-phase reaction of alkenes with ozone: formation yields of carbonyls from biradicals in ozone-alkenecyclohexane experiments. Atmos. Environ. 1998, 32, 3393−3402. (9) Gery, M. W.; Fox, D. L.; Kamens, R. M.; Stockburger, L. Investigation of hydroxyl radical reactions with o-xylene and m-xylene in a continuous stirred tank reactor. Environ. Sci. Technol. 1987, 21, 339−348. (10) Calvert, J. G.; Atkinson, R.; Becker, K. H.; Kamens, R. M.; Seinfeld, J. H.; Wallington, T. J.; Yarwood, G. The Mechanisms of Atmospheric Oxidation of Aromatic Hydrocarbons; Oxford University Press: New York, 2002. (11) Crounse, J. D.; Nielsen, L. B.; Jorgensen, S.; Kjaergaard, H. G.; Wennberg, P. O. Autoxidation of organic compounds in the atmosphere. J. Phys. Chem. Lett. 2013, 4, 3513−3520. (12) Bouzidi, H.; Fittschen, C.; Coddeville, P.; Tomas, A. Photolysis of 2,3-pentanedione and 2,3-hexanedione: kinetics, quantum yields, and product study in a simulation chamber. Atmos. Environ. 2014, 82, 250−257. (13) Djehiche, M.; Tomas, A.; Fittschen, C.; Coddeville, P. First cavity ring-down spectroscopy HO2 measurements in a large photoreactor. Z. Phys. Chem. 2011, 225, 983−992. (14) Nishanth, T.; Praseed, K. M.; Rathnakaran, K.; Satheesh Kumar, M. K.; Ravi Krishna, R.; Valsaraj, K. T. Atmospheric pollution in a semi-urban, coastal region in India following festival seasons. Atmos. Environ. 2012, 47, 295−306. (15) Jackson, A. W.; Yarwood, A. J. Radiation and radiationless processes in 2,3-pentanedione; Phosphorescence lifetime in the gas phase. Can. J. Chem. 1971, 49, 987−993. (16) Jackson, A. W.; Yarwood, A. J. Fluorescence and phosphorescence of 2,3-pentanedione. Can. J. Chem. 1972, 50, 1331−1337. (17) Szabo, E.; Djehiche, M.; Riva, M.; Fittschen, C.; Coddeville, P.; Sarzynski, D.; Tomas, A.; Dobé, S. Atmospheric chemistry of 2,3pentanedione: Photolysis and reaction with OH radicals. J. Phys. Chem. A 2011, 115, 9160−9168. (18) Djehiche, M.; Tomas, A.; Fittschen, C.; Coddeville, P. First direct detection of HONO in the reaction of methylnitrite (CH3ONO) with OH radicals. Environ. Sci. Technol. 2011, 45, 608− 614. (19) Morajkar, P.; Schoemaecker, C.; Fittschen, F. Absolute absorption cross sections for two selected lines of formaldehyde around 6625 cm−1. J. Mol. Spectrosc. 2012, 281, 18−23. (20) Barry, H. R.; Corner, L.; Hancock, G.; Peverall, R.; Ranson, T. L.; Ritchie, G. A. D. Measurements of pressure broadening coefficients of selected transitions in the 2ν5 band of formaldehyde. Phys. Chem. Chem. Phys. 2003, 5, 3106−3112. (21) Ruth, A. A.; Heitmann, U.; Heinecke, E.; Fittschen, F. The rotationally-resolved absorption spectrum of formaldehyde from 6547 to 7051 cm−1. Z. Phys. Chem. 2015, 229, 1609−1624. (22) Djehiche, M.; Le Tan, N. L.; Jain, C.; Dayma, G.; Dagaut, P.; Chauveau, C.; Pillier, L.; Tomas, A. Quantitative measurements of HO2 and other products of n-butane oxidation (H2O2,H2O, CH2O, and C2H4) at elevated temperatures by direct coupling of a jet-stirred reactor with sampling nozzle and cavity ring-down spectroscopy (cwCRDS). J. Am. Chem. Soc. 2014, 136, 16689−16694. (23) Morajkar, P.; Schoemaecker, C.; Okumura, M.; Fittschen, C. Direct measurement of the equilibrium constants of the reaction of

formaldehyde and acetaldehyde with HO2 radicals. Int. J. Chem. Kinet. 2014, 46, 245. (24) Bahrini, C.; Herbinet, O.; Glaude, P.-A.; Schoemaecker, C.; Fittschen, C.; Battin-Leclerc, F. Detection of some stable species during the oxidation of methane by coupling a jet-stirred reactor (JSR) to cw-CRDS. Chem. Phys. Lett. 2012, 534, 1−7. (25) Bahrini, C.; Morajkar, P.; Schoemaecker, C.; Frottier, O.; Herbinet, O.; Glaude, P.-A.; Battin-Leclerc, F.; Fittschen, C. Experimental and modeling study of the oxidation of n-butane in a jet stirred reactor using cw-CRDS measurements. Phys. Chem. Chem. Phys. 2013, 15, 19686. (26) Staak, M.; Gash, E. W.; Venables, D. S.; Ruth, A. A. The rotationally-resolved absorption spectrum of formaldehyde from 6547 to 6804 cm−1. J. Mol. Spectrosc. 2005, 229, 115−121. (27) Thiébaud, J.; Crunaire, S.; Fittschen, C. Measurements of line strengths in the 2ν1 band of the HO2 radical using laser photolysis/ continuous wave cavity ring-down spectroscopy (cw-CRDS). J. Phys. Chem. A 2007, 111, 6959−6966. (28) Ibrahim, N.; Thiébaud, J.; Orphal, J.; Fittschen, C. Airbroadening coefficients of the HO2 radical in the 2ν1 band measured using cw-CRDS. J. Mol. Spectrosc. 2007, 242, 64−69. (29) Morajkar, P.; Bossolasco, A.; Schoemaecker, C.; Fittschen, C. Photolysis of CH3CHO at 248 nm: Evidence of triple fragmentation from primary quantum yield of CH3 and HCO radicals and H atoms. J. Chem. Phys. 2014, 140, 214308. (30) Parker, A.; Jain, C.; Schoemaecker, C.; Szriftgiser, P.; Votava, O.; Fittschen, C. Simultaneous, time-resolved measurements of OH and HO2 radicals by coupling of high repetition rate LIF and cw-CRDS techniques to a laser photolysis reactor and its application to the photolysis of H2O2. Appl. Phys. B: Lasers Opt. 2011, 103, 725. (31) Votava, O.; Masat, M.; Parker, A. E.; Jain, C.; Fittschen, F. Microcontroller based resonance tracking unit for time resolved continuous wave cavity-ringdown spectroscopy measurements. Rev. Sci. Instrum. 2012, 83, 043110. (32) Farago, E. P.; Viskolcz, B.; Schoemaecker, C.; Fittschen, F. Absorption spectrum and absolute absorption cross sections of CH3O2 radicals and CH3I molecules in the wavelength range 7473−7497 cm−1. J. Phys. Chem. A 2013, 117, 12802. (33) Wojdyr, M. Fityk: a general-purpose peak fitting program. J. Appl. Crystallogr. 2010, 43, 1126−1128. (34) Ivanov, A. V.; Trakhtenberg, S.; Bertram, A. K.; Gershenzon, Y. M.; Molina, M. J. OH, HO2, and ozone gaseous diffusion coefficients. J. Phys. Chem. A 2007, 111, 1632−1637. (35) Atkinson, R.; Baulch, D. L.; Cox, R. A.; Crowley, J. N.; Hampson, R. F.; Hynes, R. G.; Jenkin, M. E.; Rossi, M. J.; Troe, J. Evaluated kinetic and photochemical data for atmospheric chemistry: Volume II. Gas phase reactions of organic species. Atmos. Chem. Phys. 2006, 6, 3625−4055. (36) Atkinson, R.; Baulch, D. L.; Cox, R. A.; Crowley, J. N.; Hampson, R. F.; Hynes, R. G.; Jenkin, M. E.; Rossi, M. J.; Troe, J. Evaluated kinetic and photochemical data for atmospheric chemistry: Volume I - gas phase reactions of Ox, HOx, NOx and SOx species. Atmos. Chem. Phys. 2004, 4, 1461−1738. (37) Jenkin, M. E.; Hurley, M. D.; Wallington, T. J. Investigation of the radical product channel of the CH3C(O)O2 + HO2 reaction in the gas phase. Phys. Chem. Chem. Phys. 2007, 9, 3149−3162. (38) Dillon, T. J.; Crowley, J. N. Direct detection of OH formation in the reactions of HO2 with CH3C(O)O2 and other substituted peroxy radicals. Atmos. Chem. Phys. 2008, 8, 4877−4889. (39) Blitz, M. A.; Heard, D. E.; Pilling, M. J. OH formation from CH3CO + O2: a convenient experimental marker for the acetyl radical. Chem. Phys. Lett. 2002, 365, 374−379. (40) Carr, S. A.; Glowacki, D. R.; Liang, C.-H.; Baeza Romero, M. T.; Blitz, M. A.; Pilling, M. J.; Seakins, P. W. Experimental and modeling studies of the pressure and temperature dependences of the kinetics and the OH yields in the acetyl + O2 reaction. J. Phys. Chem. A 2011, 115, 1069−1085. (41) Carr, S. A.; Baeza Romero, M. T.; Blitz, M. A.; Pilling, M. J.; Heard, D. E.; Seakins, P. W. OH yields from the CH3CO + O2 12788


Article

The Journal of Physical Chemistry A reaction using an internal standard. Chem. Phys. Lett. 2007, 445, 108− 112. (42) Baeza Romero, M. T.; Blitz, M. A.; Heard, D. E.; Pilling, M. J.; Price, B.; Seakins, P. W. OH formation from the C2H5CO + O2 reaction: An experimental marker for the propionyl radical. Chem. Phys. Lett. 2005, 408, 232−236. (43) Baeza Romero, M. T.; Blitz, M. A.; Heard, D. E.; Pilling, M. J.; Price, B.; Seakins, P. W.; Wang, L. Photolysis of methylethyl, diethyl and methylvinyl ketones and their role in the atmospheric HOx budget. Faraday Discuss. 2005, 130, 73−88. (44) Gross, C. B. M.; Dillon, T. J.; Crowley, J. N. Pressure dependent OH yields in the reactions of CH3CO and HOCH2CO with O2. Phys. Chem. Chem. Phys. 2014, 16, 10990−10998. (45) Tyndall, G. S.; Orlando, J. J.; Wallington, T. J.; Hurley, M. D. Pressure dependence of the rate coefficients and product yields for the reaction of CH3CO radicals with O2. Int. J. Chem. Kinet. 1997, 29, 655−663. (46) Kovacs, G.; Zador, J.; Farkas, E.; Nadasdi, R.; Szilagyi, I.; Dobe, S.; Berces, T.; Marta, F.; Lendvay, G. Kinetics and mechanism of the reactions of CH3CO and CH3C(O)CH2 radicals with O2. Lowpressure discharge flow experiments and quantum chemical computations. Phys. Chem. Chem. Phys. 2007, 9, 4142−4154. (47) Zügner, G. L.; Szilagyi, I.; Zador, J.; Szabo, E.; Dobé, S.; Song, X.; Wang, B. OH yields for C2H5CO + O2 at low pressure: Experiment and theory. Chem. Phys. Lett. 2010, 495, 179−181. (48) Papadimitriou, V. C.; Karafas, E. S.; Gierczak, T.; Burkholder, J. B. CH3CO + O2 + M (M = He, N2) reaction rate coefficient measurements and implications for the OH radical product yield. J. Phys. Chem. A 2015, 119, 7481. (49) Devolder, P.; Dusanter, S.; Lemoine, B.; Fittschen, C. About the co-product of the OH radical in the reaction of acetyl with O2 below atmospheric pressure. Chem. Phys. Lett. 2006, 417, 154−158. (50) Holmes, J. R.; O’Brien, R. J.; Crabtree, J. H.; Hecht, T. A.; Seinfeld, J. H. Measurement of ultraviolet radiation intensity in photochemical smog studies. Environ. Sci. Technol. 1973, 7, 519−523. (51) Plum, C. N.; Sanhueza, E.; Atkinson, R.; Carter, W. P. L.; Pitts, J. N. OH radical rate constants and photolysis rates of α-dicarbonyls. Environ. Sci. Technol. 1983, 17, 479−484. (52) Salter, R. J.; Blitz, M. A.; Heard, D. E.; Pilling, M. J.; Seakins, P. W. Pressure and temperature dependent photolysis of glyoxal in the 355−414 nm region: evidence for dissociation from multiple states. Phys. Chem. Chem. Phys. 2013, 15, 6516−6526. (53) Sander, S. P.; Abbatt, J. P. D.; Barker, J. R.; Burkholder, J. B.; Friedl, R. R.; Golden, D. M.; Huie, R. E.; Kolb, C. E.; Kurylo, M. J.; Moortgat, G. K., et al. Chemical kinetics and photochemical data for use in atmospheric studies, Evaluation No. 17; Jet Propulsion Laboratory: Pasadena, 2011; http://jpldataeval.jpl.nasa.gov. (54) Le Crâne, J.-P.; Villenave, E.; Hurley, M. D.; Wallington, T. J.; Ball, J. C. Atmospheric chemistry of propionaldehyde: Kinetics and mechanisms of reactions with OH radicals and Cl atoms, UV spectrum, and self-reaction kinetics of CH3CH2C(O)O2 radicals at 298 K. J. Phys. Chem. A 2005, 109, 11837−11850. (55) Tomas, A.; Lesclaux, R. Self-reaction kinetics of the (CH3)2CHC(O)O2 and (CH3)3CC(O)O2 acylperoxy radicals between 275 and 363 K. Chem. Phys. Lett. 2000, 319, 521−528. (56) Lesclaux, R., Combination of peroxyl radicals in the gas phase. In Peroxyl Radicals; Alfassi, Z. B., Ed.; John Wiley & Sons Ltd.: New York, 1997; pp 81−112. (57) Tomas, A.; Villenave, E.; Lesclaux, R. Reactions of the HO2 radical with CH3CHO and CH3C(O)O2 in the gas phase. J. Phys. Chem. A 2001, 105, 3505−3514. (58) Klotz, B.; Graedler, F.; Sorensen, S.; Barnes, I.; Becker, K. H. A kinetic study of the atmospheric photolysis of α-dicarbonyls. Int. J. Chem. Kinet. 2001, 33, 9−20.

12789


Low-Pressure Photolysis of 2,3-Pentanedione in Air: Quantum Yields

Recommend Documents