Photolysis Of Methyl Nitrite Research Articles

Conformer-specific geminate recombination following methyl nitrite photolysis in solution

The dynamics of the ultraviolet (UV) photoexcitation of methyl nitrite in weakly interacting perfluoromethylcyclohexane solution are investigated using transient absorption spectroscopy. UV excitation in the structured S1←S0 absorption band induces dissociation, with geminate recombination and vibrational cooling of syn and anti-conformers of methyl nitrate on a timescale of ∼56ps. Solvent-induced vibrational cooling favours relaxation to the higher-energy anti-conformer on entropic grounds, and subsequent inter-conversion to the lower-energy syn-conformer is prevented by a 3500cm–1 barrier. UV excitation to the S2 state produces a transient electronic absorption band resembling the absorption spectrum of NO2.

Gas-phase products and secondary organic aerosol formation from the ozonolysis and photooxidation of myrcene

In this study, the ozone and OH-radical reactions of myrcene were investigated in an aerosol chamber (at 292–295 K and 50% relative humidity) to examine the gas-phase oxidation products and secondary organic aerosol (SOA) formation. The ozone reaction studies were performed in the presence and absence of CO, which serves as an OH radical scavenger. In the photooxidation experiments OH radicals were generated by photolysis of methyl nitrite. The ozonolysis of myrcene in the presence of CO resulted in a substantial yield of 4-vinyl-4-pentenal (55.3%), measured as m/z 111 plus m/z 93 using proton transfer reaction-mass spectrometry (PTR-MS) and confirmed unambiguously as C7H10O by denuder measurements and HPLC/ESI-TOFMS analysis of its 2,4-dinitrophenylhydrazine (DNPH) derivative. Additionally, the formation of two different organic dicarbonyls with m/z 113 and a molecular formula of C6H8O2 were observed (2.1%). The yields of these dicarbonyls were higher in the ozonolysis experiments without an OH scavenger (5.4%) and even higher (13.8%) in the myrcene OH radical reaction. The formation of hydroxyacetone as a direct product of the myrcene reaction with ozone with a molar yield of 17.6% was also observed. The particle size distribution and volume concentrations were monitored and facilitated the calculation of SOA yields, which ranged from 0 to 0.01 (ozonolysis in the presence of CO) to 0.39 (myrcene OH radical reaction). Terpenylic acid was found in the SOA samples collected from the ozonolysis of myrcene in the absence of an OH scavenger and the OH radical-initiated reaction of myrcene but not in samples collected from the ozonolysis in the presence of CO as an OH radical scavenger, suggesting that terpenylic acid formation involves the reaction of myrcene with an OH radical. A reaction mechanism describing the formation of terpenylic acid is proposed.

First Direct Detection of HONO in the Reaction of Methylnitrite (CH3ONO) with OH Radicals

We report on the development of a new environmental simulation chamber coupled with an in situ continuous wave cavity ring-down spectrometer operating in the near IR (∼1.5 μm). The first application reported in this paper dealt with the chemical mechanism of UV photolysis of methyl nitrite (CH(3)ONO) in air. HONO has been detected for the first time and shown to be formed in the OH + CH(3)ONO reaction. A dense spectrum of cis-HONO absorption lines has been observed near 1.5 μm, in agreement with a previous study (Guilmot et al.). CH(2)O has been measured as primary product with good sensitivity and time resolution. In contrast to Zhao et al., we did not detect any NO(2) absorption features in this wavelength range. Calibration experiments provided very low NO(2) absorption cross sections in this region (∼10(-25) cm(2)), leading to conclude that NO(2) cannot be observed in this wavelength range in the presence of equal amounts of CH(2)O.

ChemInform Abstract: The Photooxidation of Methyl Tertiary Butyl Ether.

Methyl tertiary butyl ether (MTBE) has been proposed and is being used as an additive to increase the octane of gasoline without the use of tetraethyl lead and alkylbenzenes. The present experiments have been performed to examine the kinetics and mechanisms of the atmospheric removal of MTBE. The kinetics of the reaction of OH with MTBE was examined by using a relative rate technique in which photolysis of methyl nitrite was used as the source of OH. With n-butane as the reference compound a value of (2.99 ± 0.12) × 10−12 cm3 molecule−1 s−1 at a temperature of 298 K was obtained for the rate constant. The products (and product yields) for the OH reaction with MTBE in the presence of NOx were also determined and found to be t-butyl formate (0.68 ± 0.05), methyl acetate (0.14 ± 0.02), acetone (0.026 ± 0.003), t-butanol (0.062 ± 0.009), and formaldehyde (0.48 ± 0.05) in mols/mol MTBE converted. The OH rate constant for the major product formed, t-butyl formate was also measured and found to be (7.37 ± 0.05) × 10−13 cm3 molecule−1 s−1. Mechanisms to rationalize the formation of the products are presented.

ChemInform Abstract: Relative Rate Constant Measurements for the Gas-Phase Reactions of Hydroxyl Radicals with 4-Methyl-2-pentanone, trans-4-Octene, and trans- 2-Heptene

The relative OH reaction rates from the simulated atmospheric oxidation of 4-methyl-2-pentanone, trans-4-octene, and trans-2-heptene have been measured. Reactions were carried out at 297 ± 2 K in 100-liter FEP Teflon®-film bags. The OH radicals were produced from the photolysis of methyl nitrite. The measured rate constants (×1011 cm3 molecule−1 s−1) were as follows: 6.77 ± 0.50 for trans-4-octene, 1.40 ± 0.07 for 4-methyl-2-pentanone, and 6.70 ± 0.23 for trans-2-heptene using an absolute rate constant of 2.63 × 1011 cm3 molecule−1 s−1 for the reaction of OH with propene; the principal reference organic. © John Wiley & Sons, Inc.

Photodissociation Dynamics of Alkyl Nitrites at 266 and 355 nm: The OH Product Channel

Photodissociation of methyl nitrite and n-butyl nitrite at 266 and 355 nm has been investigated in the gas phase at room temperature. OH photoproducts were observed, and their internal state distributions were measured by the one-photon laser-induced fluorescence (LIF) technique. It was found that the nascent OH from the 266 nm photolysis of methyl nitrite was vibrationally cold, and its rotational state distribution conformed to a Boltzmann behavior with a rotational temperature of T(rot) = 2200 +/- 150 K. In contrast, the nascent OH from the 266 nm photolysis of n-butyl nitrite was found to be vibrationally excited, and the measured relative population of v'' = 0:1 was 0.78:0.22. The rotational state distribution of the OH v'' = 1 state conformed to Boltzmann behavior, with a rotational temperature of T(rot) = 1462 +/- 120 K. However, a simple Boltzmann distribution was not found for the OH v'' = 0 state. In the photolysis of n-butyl nitrite at 355 nm, the OH fragment was found to be vibrationally cold and its rotational state distribution showed non-Boltzmann behavior. A photodissociation mechanism involving an intramolecular hydrogen atom transfer process is proposed for the OH product pathway for methyl nitrite, which has been compared with the potential energy surfaces obtained from density functional theory (DFT) calculations. A photodissociation mechanism of n-butyl nitrite is also proposed for the OH product pathway, which differs from that of methyl nitrite due to the effects of the different alkoxy substituents.

Measurement and calculation of the rate constant for the reaction of isopropyl isocyanate with hydroxyl radical

AbstractThe rate constant for the gas‐phase reaction of hydroxyl radical with isopropyl isocyanate (IIC) has been measured, relative to toluene, in the T = 287–321 K range at atmospheric pressure in air. Ultraviolet photolysis of methyl nitrite served as the source of hydroxyl radical. The experimental Arrhenius expression obtained for this reaction is 7.09 × 10−13 × exp[(307 ± 263)/T] cm3 molecule−1 s−1, where the indicated error is one least‐squares standard deviation and does not include the uncertainty in the rate constant for toluene. Multilevel ab initio calculations, performed at the MP‐SAC2 level, indicate that hydrogen atom transfer from the tertiary carbon atom occurs without an energy barrier, in agreement with the experimentally observed slight negative temperature dependence of the rate constant. The calculations indicate that hydrogen‐bonded complexes of IIC and OH form in the reactant entrance channels along the minimum‐energy paths. Use of conventional transition state theory and MP‐SAC2 scaled transition state relative energies, with an asymmetric Eckart tunneling model for transfer of a hydrogen atom from a methyl group, yields a theoretical rate constant of 1.81 × 10−18 × T2 × exp(744/T) cm3 molecule−1 s−1 in the T = 200–350 K range. From the rate constant data, an estimated upper limit for the tropospheric lifetime of IIC is determined as 6.0 days at 15°C, based on the global weighted‐average OH concentration of 9.4 × 105 molecules cm−3 determined by Prinn et al. (Science 2001, 292, 1882–1888). © 2008 Wiley Periodicals, Inc. Int J Chem Kinet 41: 187–197, 2009

Atmospheric Reaction of OH Radicals with 1,3-Butadiene and 4-Hydroxy-2-butenal

The gas-phase reaction of OH radicals with 1,3-butadiene and 4-hydroxy-2-butenal in the presence of NO has been studied in a flow tube operated at 295 +/- 2 K and pressures of 950 mbar of synthetic air or 100 mbar of an O(2)/He mixture. OH radicals were generated using three different experimental approaches, namely, ozonolysis of tetramethylethylene (dark reaction), photolysis of methyl nitrite, or via the reaction of HO(2) with NO (HO(2) from the reaction of H-atoms with O(2)). Products of the reaction of OH radicals with 1,3-butadiene were HCHO (0.64 +/- 0.08), acrolein (0.59 +/- 0.06), 4-hydroxy-2-butenal (0.23 +/- 0.10), furan (0.046 +/- 0.014), and organic nitrates (0.06 +/- 0.02) accounting for more than 90% of the reacted carbon. There was no significant dependence of product yields on experimental conditions which were varied in a wide range. The formation of the 1,4-addition product 4-hydroxy-2-butenal was confirmed unambiguously for the first time. The rate coefficient k(OH + 4-hydroxy-2-butenal) = (5.1 +/- 0.8) x 10(-11) cm(3) molecule(-1) s(-1) was determined using a relative rate technique (p = 100 mbar, T = 295 +/- 2 K). Products of the reaction of OH radicals with 4-hydroxy-2-butenal were glycolaldehyde (0.40 +/- 0.06), glyoxal (0.17 +/- 0.04), trans-butenedial (0.093 +/- 0.033), and organic nitrates (0.043 +/- 0.015) as well as further carbonylic substances remaining unidentified so far. Corresponding reaction mechanisms describing the formation of the detected products are proposed, and the relevance of these data for atmospheric conditions is discussed.

Use of integrated cavity output spectroscopy for studying gas phase chemistry in a smog chamber: Characterizing the photolysis of methyl nitrite (CH 3ONO)

We report on the first demonstration of the study of photo-induced reaction products in a smog chamber by means of wavelength modulated off-axis integrated cavity output spectroscopy (WM-OA-ICOS) at 1.511 μm. The preliminary results of the photolysis of methyl nitrite (CH 3ONO) are presented which demonstrates the ability of our system for the degradation mechanisms studies of atmospheric relevant organic compounds.

Formation of phenol and carbonyls from the atmospheric reaction of OH radicals with benzene

The gas-phase reaction of OH radicals with benzene has been studied in a flow tube operated at 295 +/- 2 K and 950 mbar of synthetic air or O2. Ozonolysis of tetramethylethylene (dark reaction) with a measured OH radical yield of 0.92 +/- 0.08 or photolysis of methyl nitrite in the presence of NO served as the OH sources. For investigations in the presence of NOx, the conditions were chosen so that more than 95% of the OH/benzene adduct reacted with O2 even for the highest NO2 concentration occurring in the experiment. In the absence of NOx, a phenol yield from the reaction of OH radicals with benzene of 0.61 +/- 0.07 was measured by means of long-path FT-IR and UV spectroscopy over a wide range of experimental conditions. This yield was confirmed by measurements performed in the presence of NOx. Detected carbonyls were glyoxal, cis-butenedial and trans-butenedial with formation yields of 0.29 +/- 0.10, 0.08 +/- 0.03 and 0.023 +/- 0.007, respectively, measured in synthetic air and in the presence of NOx. There was no significant difference in the product yields applying both experimental approaches for OH generation (dark reaction or photolysis). Nitrobenzene and o-nitrophenol were detected in traces. The yield of nitrobenzene increased with increasing NOx resulting in a maximum formation yield of 0.007. The detected products in the presence of NOx account for approximately 78% of the reacted carbon. Butenedial yields from benzene degradation are reported for the first time. In the absence of NOx, glyoxal, cis-butenedial and trans-butenedial were also detected, but with distinctly lower yields compared to the experiments with NOx.

Rate Constant for the Reaction of OH Radicals with Isoprene at 298±2 K

Abstract Using the relative-rate technique, the rate constant for the reaction of OH radicals with isoprene was determined in one atmosphere of air at 298±2 K. Methyl nitrite photolysis in air was used as a source of OH radicals. Ozone and O-atom reactions with isoprene were confirmed to have a negligible contribution on the loss of isoprene. The rate constant relative to three reference compounds yielded (10.4±0.4)×10−11 cm3 molecule−1 s−1 (the uncertainty is 2σ).

Kinetics of the reactions of OH with 3‐methyl‐2‐cyclohexen‐1‐one and 3,5,5‐trimethyl‐2‐cyclohexen‐1‐one under simulated atmospheric conditions

AbstractRelative rate coefficients for the reactions of OH with 3‐methyl‐2‐cyclohexen‐1‐one and 3,5,5‐trimethyl‐2‐cyclohexen‐1‐one have been determined at 298 K and atmospheric pressure by the relative rate technique. OH radicals were generated by the photolysis of methyl nitrite in synthetic air mixtures containing ppm levels of nitric oxide together with the test and reference substrates. The concentrations of the test and reference substrates were followed by gas chromatography. Based on the value k(OH + cyclohexene) = (6.77 ± 1.35) × 10−11 cm3 molecule−1 s−1, rate coefficients for k(OH + 3‐methyl‐2‐cyclohexen‐1‐one) = (3.1 ± 1.0) × 10−11 and k(OH + 3,5,5‐trimethyl‐2‐cyclohexen‐1‐one) = (2.4 ± 0.7) × 10−11 cm3 molecule−1 s−1 were determined. To test the system we also measured k(OH + isoprene) = (1.11 ± 0.23) × 10−10 cm3 molecule−1 s−1, relative to the value k(OH + (E)‐2‐butene) = (6.4 ± 1.28) × 10−11 cm3 molecule−1 s−1. The results are discussed in terms of structure–activity relationships, and the reactivities of cyclic ketones formed in the photo‐oxidation of monoterpene are estimated. © 2001 John Wiley & Sons, Inc. Int J Chem Kinet 34: 7–11, 2002

Kinetics and mechanism of the atmospheric oxidation of tertiary amyl methyl ether

AbstractTertiary‐amyl methyl ether (TAME) is proposed for use as an additive to increase the oxygen content of gasoline as stipulated in the 1990 Clean Air Amendments. The present experiments have been performed to examine the kinetics and mechanisms of the atmospheric removal of TAME. The kinetics of the reaction of OH with TAME was examined by using a relative rate technique in which photolysis of methyl nitrite or nitrous acid was used as the source of OH. The OH rate constant for TAME and two major products (t‐amyl formate and methyl acetate) were measured and yields for ten products were determined as primary products from the reaction.Values determined for the rate constants for the reaction with OH were 5.48 × 10−12 (TAME), 1.75 × 10−12 (t‐amyl formate), and 3.85 × 10−13 cm3 molec−1 s−1 (methyl acetate) at 298 ± 2 K. The primary products (with corrected yields where required) from the OH + TAME that have been observed include (1) t‐amyl formate (0.366), methyl acetate (0.349), acetaldehyde (0.43, corrected), acetone (0.036), formaldehyde (0.549), t‐amyl alcohol (0.026), 3‐methyoxy‐3‐methyl‐butanal (0.044, corrected), t‐amyloxy methyl nitrate (0.029), 3‐methyoxy‐3‐methyl‐2‐butyl nitrate (0.010), and 2‐methoxy‐2‐methyl butyl nitrate (0.004). Mechanisms leading to these products involve OH abstraction from each of the four different hydrogen atoms of TAME. © 1995 John Wiley & Sons, Inc.

Kinetics of the reactions of OH radicals with selected acetates and other esters under simulated atmospheric conditions

AbstractThe relative hydroxyl radical reaction rate constants from the simulated atmospheric oxidation of selected acetates and other esters have been measured. Reactions were carried out at 297 ± 2 K in 100‐liter FEP Teflon®‐film bags. The OH radicals were generated from the photolysis of methyl nitrite in pure air. Using a rate constant of 2.63 × 10−11 cm3 molecule−1 s−1 for the reaction of OH radicals with propene, the principal reference organic compound, the rate constants (×1012 cm3 molecule−1 s−1) obtained for the acetates and esters used in this study are: n–propyl acetate 3.42 ± 0.87 n–butyl acetate 5.71 ± 0.94 n–pentyl acetate 7.53 ± 0.48 2–ethoxyethyl acetate 10.56 ± 1.31 2–ethoxyethyl isobutyrate 13.56 ± 2.32 2–ethoxyethyl methacrylate 27.22 ± 2.06 4–pentene‐1‐yl acetate 43.40 ± 3.85 3–Ethoxyacrylic acid ethyl ester 33.30 ± 1.22 Error limits represent 2σ from linear least‐squares analysis of data.A linear correlation was observed for a plot of the measured relative rate constants vs. the number of CH2 groups per molecule of the following acetates: methyl acetate, ethyl acetate, n‐propyl acetate, butyl acetate, and pentyl acetate. © 1993 John Wiley & Sons, Inc.

Rate constants and atmospheric lifetimes for the reactions of OH radicals and Cl atoms with haloalkanes

AbstractRate constants for the reactions of Cl atoms and OH radicals with haloalkanes were measured using the relative rate technique. From these values the atmospheric lifetimes of the organics with respect to Cl atoms and OH radicals were calculated. Cl atoms were produced by the photolysis of chlorine gas, and photolysis of methyl nitrite was the source of OH radicals. The rate constants were measured for a series of brominated and chlorinated alkanes for which measurements have not yet been reported excepting: k(Cl + 1‐chloropropane) and k(OH + 1‐chloropropane, 2‐chloropropane, and bromoethane). The organics studied were 1‐chloropropane, 2‐chloropropane, 1,3 dichloropropane, 2‐chloro 2methylpropane, bromoethane, 1‐bromopropane, 2‐bromopropane, 1‐bromobutane, 1‐bromopentane, and 1‐bromohexane. Cl atom reactions were measured at 298 K, the OH radical reactions were measured at temperatures between 298–308 K. © 1993 John Wiley & Sons, Inc.

Relative rate constant measurements for the gas‐phase reactions of hydroxyl radicals with 4‐methyl‐2‐pentanone, trans‐4‐octene, and trans‐2‐heptene

AbstractThe relative OH reaction rates from the simulated atmospheric oxidation of 4‐methyl‐2‐pentanone, trans‐4‐octene, and trans‐2‐heptene have been measured. Reactions were carried out at 297 ± 2 K in 100‐liter FEP Teflon®‐film bags. The OH radicals were produced from the photolysis of methyl nitrite. The measured rate constants (×1011 cm3 molecule−1 s−1) were as follows: 6.77 ± 0.50 for trans‐4‐octene, 1.40 ± 0.07 for 4‐methyl‐2‐pentanone, and 6.70 ± 0.23 for trans‐2‐heptene using an absolute rate constant of 2.63 × 1011 cm3 molecule−1 s−1 for the reaction of OH with propene; the principal reference organic. © John Wiley & Sons, Inc.

Kinetics and mechanism of the atmospheric oxidation of Ethyl tertiary butyl ether

AbstractEthyl tertiary butyl ether (ETBE) is being proposed as an additive for use in reformulated gasolines. In this study, experiments were performed to examine the kinetics and mechanism of the atmospheric removal of ETBE. The kinetics of the reaction of ETBE with OH radicals were examined by using a relative rate technique with the photolysis of methyl nitrite to generate OH radicals. With n‐hexane as the reference compound, a value of (9.73 ± 0.33) × 10−12 cm3 molecule−1 s−1 was obtained for the rate constant. The OH rate constant for t‐butyl acetate, a product of the oxidation of ETBE, was (4.4 ± 0.4) × 10−13 cm3 molecule−1 s−1 at 298 K.The primary products and molar yields for the OH reaction with ETBE in the presence of NOx were t‐butyl formate (0.64 ± 0.03), t‐butyl acetate (0.13 ± 0.01), ethyl acetate (0.043 ± 0.003), acetaldehyde (0.16 ± 0.01), acetone (0.019 ± 0.002), and formaldehyde (0.53 ± 0.04). Under the described reaction conditions, the formation of t‐butyl nitrite was also observed. From these molar yields, approximately 98% of the reacted ETBE could be accounted for by paths leading to these products. Chemical mechanisms to explain the formation of these products are presented.

Atmospheric photooxidation of isoprene part I: The hydroxyl radical and ground state atomic oxygen reactions

AbstractThe OH reaction with isoprene is studied. Methyl nitrite photolysis experiments were carried out in an outdoor smog chamber in an attempt to identify as completely as possible OH‐isoprene product distribution. Emphasis was placed on identification and quantification of oxygenated products. A Tenax‐based cryo‐trap thermal desorber used to trap, concentrate, and dry chamber samples for identification on a GC/MS is described. Analysis of the products revealed that O(3P) can form in reaction systems designed to study OH reactions that include high concentrations of NO, and consequently NO2, hence, this reaction is also examined. The yields of methacrolein and methyl vinyl ketone are determined as 25 ± 3 and 35.5 ± 4%, respectively, with an additional 4 ± 2% as 3‐methyl furan, totaling 65 ± 4%. These results, combined with those of previous studies allow 80% of isoprene's products to be explicitly identified, and the general structure of the remaining products to be ascertained. The O(3P) reaction produces 84 ± 8% epoxides, and 8 ± 3% species which result in production of HO2, and subsequently, OH. A heretofore unidentified product of the O(3P) reaction, 2‐methyl 2‐butenal, is identified. The rate constant of the NO2‐isoprene reaction is measured.

The photooxidation of methyl tertiary butyl ether

AbstractMethyl tertiary butyl ether (MTBE) has been proposed and is being used as an additive to increase the octane of gasoline without the use of tetraethyl lead and alkylbenzenes. The present experiments have been performed to examine the kinetics and mechanisms of the atmospheric removal of MTBE. The kinetics of the reaction of OH with MTBE was examined by using a relative rate technique in which photolysis of methyl nitrite was used as the source of OH. With n‐butane as the reference compound a value of (2.99 ± 0.12) × 10−12 cm3 molecule−1 s−1 at a temperature of 298 K was obtained for the rate constant. The products (and product yields) for the OH reaction with MTBE in the presence of NOx were also determined and found to be t‐butyl formate (0.68 ± 0.05), methyl acetate (0.14 ± 0.02), acetone (0.026 ± 0.003), t‐butanol (0.062 ± 0.009), and formaldehyde (0.48 ± 0.05) in mols/mol MTBE converted. The OH rate constant for the major product formed, t‐butyl formate was also measured and found to be (7.37 ± 0.05) × 10−13 cm3 molecule−1 s−1. Mechanisms to rationalize the formation of the products are presented.

Kinetics of the reactions of hydroxyl radicals with aliphatic ethers studied under simulated atmospheric conditions: Temperature dependences of the rate coefficients

Rate coefficients have been measured for the reactions of hydroxyl radicals with five aliphatic ethers over the temperature range 242–328 K. Competitive studies were carried out in an atmospheric flow reactor in which the hydroxyl radicals were generated by the photolysis of methyl nitrite in the presence of air containing nitric oxide. The reaction of OH with 2,3-dimethyl-butane was used as the reference reaction and the following Arrhenius parameters have been obtained for the reactions: OH+ROR→products: