Reaction of Oxygen Atoms, O(3P), with Ethylene in Liquid Nitrogen Solution

1973 ◽  
Vol 51 (3) ◽  
pp. 373-381 ◽  
Author(s):  
Shun-Ichi Hirokami ◽  
R. J. Cvetanović
Keyword(s):  
Quantum Yield ◽  
Ethylene Oxide ◽  
Molecular Oxygen ◽  
Liquid Nitrogen ◽  
Rate Constant ◽  
Ground State ◽  
Relative Rate ◽  
Quantum Yields ◽  
Relative Rate Constant ◽  
Oxygen Atoms

The reaction of ground-state oxygen atoms, O(3P), with ethylene and ethylene-d4 in liquid nitrogen solution at 77° K has been studied. The major and perhaps the exclusive products are ethylene oxide and acetaldehyde. The ratio of acetaldehyde to ethylene oxide is 1.2 ± 0.1 for ethylene and 0.91 ± 0.09 for ethylene-d4. Much smaller amounts of formaldehyde and trace quantities of cyclopropane are also observed.The effect of the concentration of ethylene on the quantum yields of addition products was measured. A limiting quantum yield of oxygen atoms scavenged by ethylene to form the addition products was 0.12 + 0.01. The low quantum yield suggests an appreciable cage recombination of the ground-state oxygen atoms with the trace amounts of molecular oxygen present. The effect of the concentration of added oxygen on the product yields and the relative rate constant for the addition of O(3P) to molecular oxygen and to ethylene were determined. The ratio [Formula: see text] is 6.0 ± 1.0 and the relative rate constant for the addition of O(3P) to ethylene and to ethylene-d4, [Formula: see text], is 2.0 ± 0.1.The type of products formed and the isotope effects observed are discussed in terms of the mechanism of addition of O(3P) atoms to ethylene.

The Reaction of S(3P) Atoms with Molecular Oxygen

1971 ◽  
Vol 49 (10) ◽  
pp. 1659-1664 ◽  
Author(s):  
R. W. Fair ◽  
A. Van Roodselaar ◽  
O. P. Strausz
Keyword(s):  
Molecular Oxygen ◽  
Rate Constant ◽  
Ground State ◽  
Vacuum Ultraviolet ◽  
Flash Photolysis ◽  
Ultraviolet Region ◽  
Kinetic Spectroscopy ◽  
Vacuum Ultraviolet Region

The rate constant of the reaction of ground state S(3P) atoms with molecular oxygen, S(3P) + O2(X3Σg−) → SO(X3Σ−) + O(3P), has been determined as (1.7 ± 0.2) × 1012 cm3 mol−s− at 298 °K by means of kinetic spectroscopy in the vacuum ultraviolet region. The source of S(3P) atoms was the isothermal flash photolysis of COS in the presence of Ar or CO2.

Collisional deactivation of singlet methylene in the photolysis of ketene

1969 ◽  
Vol 47 (18) ◽  
pp. 3345-3353 ◽  
Author(s):  
R. A. Cox ◽  
K. F. Preston
Keyword(s):  
Carbon Monoxide ◽  
Quantum Yield ◽  
Ground State ◽  
Inert Gases ◽  
Inert Gas ◽  
Quantum Yields ◽  
Electronic Relaxation ◽  
Excited Singlet ◽  
State Formula ◽  
Singlet Methylene

An investigation has been made into the effect of inert gas additions on product quantum yields for the photolysis at 2800 and 2490 Å of mixtures of ketene and oxygen and for the photolysis at 2800 Å of mixtures of ketene and carbon monoxide. Concentration ratios of O2 (or CO) to CH2CO were chosen so that the reaction of CH2(3Σg−) with CH2CO could be ignored and C2H4 formation could be attributed entirely to the reaction[Formula: see text]Quenching of the C2H4 quantum yield by inert gases was interpreted in terms of collisional deactivation of CH2(1A1) to the ground state[Formula: see text]and rate constant ratios k2/k1 have been determined for a number of gases: He (0.018), Ar (0.014), Kr (0.033), Xe (0.074), N2 (0.052), N2O (0.10), CF4 (0.047), C2F6 (0.11), and SF6 (0.045). It has been assumed that collision-induced intersystem crossover in excited singlet ketene makes an insignificant contribution to the observed quenching effects, but it has not been possible to verify this assumption experimentally. The mechanism of collision-induced electronic relaxation of singlet methylene is discussed in the light of the results.

THE SECONDARY HYDROGEN ISOTOPE EFFECTS IN THE PYROLYSIS OF ETHYL-d5 ACETATE AND ETHYL ACETATE-d3

1960 ◽  
Vol 38 (9) ◽  
pp. 1407-1411 ◽  
Author(s):  
Arthur T. Blades ◽  
P. W. Gilderson
Keyword(s):  
Ethyl Acetate ◽  
Rate Constant ◽  
Hydrogen Isotope ◽  
Experimental Error ◽  
Relative Rate ◽  
Isotope Effects ◽  
Relative Rate Constant ◽  
Temperature Ranges ◽  
Relative Rate Constants ◽  
Constant Expression

Rate constant expressions have been obtained for ethyl acetate and ethyl-d5 acetate in the temperature ranges 500–603 °C and 501–614 °C.[Formula: see text]By measuring the relative rate of production of C2H4 and C2D4 from identical mixtures of the two esters at the temperatures 387 and 490 °C, it has been possible to determine the temperature coefficient of the relative rate constant more accurately. This, coupled with the relative rate constants at 500 °C derived from the above equations, gives the relative rate constant expression.[Formula: see text]These data are compared with the intramolecular isotope effect in the decomposition of ethyl-1,1,2,2-d4 acetate, and the differences attributed to secondary isotope effects.The rate of decomposition of ethyl acetate-d3 was found to be identical within experimental error with that of the normal acetate.

scholarly journals Evidence of the water-cage effect on the photolysis of NO<sub>3</sub><sup>-</sup> and FeOH<sup>2+</sup>, and its implications for the photochemistry at the air-water interface of atmospheric droplets

2009 ◽  
Vol 9 (3) ◽  
pp. 13123-13153
Author(s):  
P. Nissenson ◽  
D. Dabdub ◽  
R. Das ◽  
V. Maurino ◽  
C. Minero ◽  
...  
Keyword(s):  
Surface Layer ◽  
Quantum Yield ◽  
Rate Constant ◽  
Large Fraction ◽  
Quantum Yields ◽  
Yield Data ◽  
Photolysis Rate ◽  
Air Water Interface ◽  
Reduced Water ◽  
Rate Constant Distribution

Abstract. Experiments are conducted to determine the photolysis quantum yields of nitrate, FeOH2+, and H2O2 in the bulk and at the surface layer of water. Results show that the quantum yields of nitrate and FeOH2+ are enhanced at the surface compared to the bulk due to a reduced water-cage surrounding the photo-fragments (•OH+•NO2 and Fe2++•OH, respectively). However, no evidence is found for an enhanced quantum yield for H2O2 at the surface. The photolysis rate constant distribution within nitrate, FeOH2+, and H2O2 aerosols is calculated by combining the quantum yield data with Mie theory calculations of light intensity. Values for the photolysis rate constant of nitrate and FeOH2+ are significantly higher at the surface than in the bulk due to enhanced quantum yields at the surface. The results concerning the rates of photolysis of these photoactive species are applied to the assessment of the reaction between benzene and •OH in the presence of •OH scavengers in an atmospherically relevant scenario. For a droplet of 1μm radius, a large fraction of the total •OH-benzene reaction (15% for H2O2, 20% for nitrate, and 35% for FeOH2+) occurs in the surface layer, which accounts for just 0.15% of the droplet volume. By neglecting the surface effects on photochemistry, the rate of the important reactions could be underestimated by a considerable amount.

Solvent effect on the reactivity of monosubstituted phenols towards singlet molecular oxygen (O2(1Δg)) in alkaline media

1993 ◽  
Vol 71 (8) ◽  
pp. 1247-1252 ◽  
Author(s):  
Marta Luiz ◽  
María I. Gutiérrez ◽  
Graciela Bocco ◽  
Norman A. García
Keyword(s):  
Molecular Oxygen ◽  
Rate Constant ◽  
Reaction Pathway ◽  
Aqueous Media ◽  
Solvent Polarity ◽  
Alkaline Media ◽  
Quantum Yields ◽  
Quenching Rate ◽  
Singlet Molecular Oxygen ◽  
Quenching Rate Constant

The influence of solvent polarity on the dye-sensitized photooxidation (singlet molecular oxygen (O2(1Δg)) mediated) of a series of para-substituted phenolates was studied. Kinetic evidence obtained shows that the overall and the pure chemical interactions, phenolate–O2(1Δg), depend on the solvent polarity in a different way. This is clearly reflected in the efficiency of O2(1Δg) photooxidation of the substrates: surprisingly, the photooxidation quantum yield increases as the overall quenching rate constant decreases. The substrate photooxidation quantum yields obtained ranged from 0.05 to 0.15, the upper limit corresponding to a moderately polar medium (a benzene–methanol mixture) and the lower to an aqueous medium. We conclude that a high solvent polarity favours only the obtainment of the encounter complex (O2(1Δg)–phenolate), whereas the reactive step is affected in much the same way as those processes where charges are neutralized along the reaction pathway. The results obtained are discussed in terms of a partly polar excited state complex between O2(1Δg) and the phenolates. The rate constant for the reactive pathway in both organic and aqueous media is correlated with the Hammet-type substituent constant R−.

scholarly journals Notable Substituent Effects on the Rate Constant of Thermal Denitrogenation of Cyclic Azoalkanes: Strong Evidence for a Stepwise Denitrogenation Mechanism

2010 ◽  
Vol 63 (12) ◽  
pp. 1615 ◽  
Author(s):  
Chizuko Ishihara ◽  
Manabu Abe
Keyword(s):  
Rate Constant ◽  
Linear Correlation ◽  
Strong Evidence ◽  
Bond Cleavage ◽  
Relative Rate ◽  
Substituent Effects ◽  
Relative Rate Constant ◽  
Rate Determining Step ◽  
Singlet Diradicals ◽  
Type Radical

The thermal denitrogenation rates (k) of a series of 7,7-dimethoxy-1,4-diaryl-2,3-diazabicyclo[2.2.1]hept-2-ene derivatives 2 with a variety of aryl groups (p-CNC6H4, C6H5, p-MeC6H4, p-MeOC6H4) were determined to investigate the denitrogenation mechanism. A linear correlation (r = 0.988) between the relative rate-constant (log krel) of the denitrogenation reaction and Arnold’s σα• parameter for benzylic-type radical-stabilization was observed. However, the relative rate-constant was not correlated with the substituent effect on the lifetime of the resulting singlet diradicals DR2. These results indicate that the rate-determining step of denitrogenation of 7,7-dimethoxy-2,3-diazabicyclo[2.2.1]hept-2-ene derivatives involves stepwise C–N bond cleavage.

scholarly journals Atmospheric isoprene ozonolysis: impacts of stabilized Criegee intermediate reactions with SO<sub>2</sub>, H<sub>2</sub>O and dimethyl sulfide

2015 ◽  
Vol 15 (6) ◽  
pp. 8839-8881 ◽  
Author(s):  
M. J. Newland ◽  
A. R. Rickard ◽  
L. Vereecken ◽  
A. Muñoz ◽  
M. Ródenas ◽  
...  
Keyword(s):  
Rate Constant ◽  
Dimethyl Sulfide ◽  
Relative Rate ◽  
Full Range ◽  
Substantial Contribution ◽  
Sulfide Concentration ◽  
Relative Rate Constant ◽  
So2 Oxidation ◽  
Experimental Conditions ◽  
So2 Removal

Abstract. Isoprene is the dominant global biogenic volatile organic compound (VOC) emission. Reactions of isoprene with ozone are known to form stabilised Criegee intermediates (SCIs), which have recently been shown to be potentially important oxidants for SO2 and NO2 in the atmosphere; however the significance of this chemistry for SO2 processing (affecting sulfate aerosol) and NO2 processing (affecting NOx levels) depends critically upon the fate of the SCI with respect to reaction with water and decomposition. Here, we have investigated the removal of SO2 in the presence of isoprene and ozone, as a function of humidity, under atmospheric boundary layer conditions. The SO2 removal displays a clear dependence on relative humidity, confirming a significant reaction for isoprene derived SCI with H2O. Under excess SO2 conditions, the total isoprene ozonolysis SCI yield was calculated to be 0.56 (±0.03). The observed SO2 removal kinetics are consistent with a relative rate constant, k(SCI + H2O)/k(SCI + SO2), of 5.4 (±0.8) × 10−5 for isoprene derived SCI. The relative rate constant for k(SCI decomposition)/k(SCI + SO2) is 8.4 (±5.0) × 1010 cm−3. Uncertainties are ±2σ and represent combined systematic and precision components. These kinetic parameters are based on the simplification that a single SCI species is formed in isoprene ozonolysis, an approximation which describes the results well across the full range of experimental conditions. Our data indicate that isoprene-derived SCIs are unlikely to make a substantial contribution to gas-phase SO2 oxidation in the troposphere. We also present results from an analogous set of experiments, which show a clear dependence of SO2 removal in the isoprene-ozone system as a function of dimethyl sulfide concentration. We propose that this behaviour arises from a rapid reaction between isoprene-derived SCI and DMS; the observed SO2 removal kinetics are consistent with a relative rate constant, k(SCI + DMS)/k(SCI + SO2), of 4.1 (±2.2). This result suggests that SCIs may contribute to the oxidation of DMS in the atmosphere and that this process could therefore influence new particle formation in regions impacted by emissions of unsaturated hydrocarbons and DMS.

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