THE REACTION OF ETHANOL VAPOR WITH Hg 6(3P1) ATOMS

1961 ◽  
Vol 39 (12) ◽  
pp. 2466-2473 ◽  
Author(s):  
Arthur R. Knight ◽  
Harry E. Gunning
Keyword(s):  
Dark Period ◽  
Hydrogen Abstraction ◽  
Ethanol Vapor ◽  
Continuous Illumination ◽  
Quantum Yields ◽  
Maximum Value ◽  
Volatile Products ◽  
Intermittent Illumination ◽  
Heavy Product ◽  
Static Conditions

The reaction of ethanol vapor with Hg 6(3P1) atoms has been investigated under static conditions at 25 °C. To determine the nature and efficiency of the primary process, the reaction has been studied in the presence of nitric oxide, and also under conditions of inter mittent illumination. For the pure substrate the volatile products were H2 (0.53), CH3CHO (0.08), CO (0.025), C2H6 (0.006), and CH4 (0.002), with the bracketed numbers representing the quantum yields at zero exposure time. The heavy product was a mixture of butanediols containing 90% 2,3-, 8% 1,3-, and 2% 1,4-butanediol. With 20% added NO, the products were EtONO (0.25), N2O (0.14), H2O, and H2 (0.017). Under intermittent illumination, the quantum yield (Φ) of H2 formation for pure substrate was measured as a function of the light period (tL) and the dark period (tD). For maximum values of Φ(H2), it was found that tD had to exceed ca. 120 msec. Under these conditions, Φ(H2) rose linearly with decreasing log tL, to a maximum value of 0.96 at tL less than 0.4 msec.From the study it is concluded that ethanol reacts with Hg 6(3P1) atoms to form ethoxy radicals and H atoms with at least 96% efficiency. The primary ethoxy radicals disappear by hydrogen abstraction from the substrate to form mainly CH3CHOH radicals. Under continuous illumination the low value (0.53) for Φ(H2) is caused principally by the addition of H atoms to the CH3CHOH radicals.

THE REACTION OF ISOPROPANOL VAPOR WITH Hg 6 (3P1) ATOMS: PART I. PURE SUBSTRATE

1962 ◽  
Vol 40 (6) ◽  
pp. 1134-1139 ◽  
Author(s):  
Arthur R. Knight ◽  
Harry E. Gunning
Keyword(s):  
Quantum Yield ◽  
Hydrogen Production ◽  
Exposure Time ◽  
Resonance Line ◽  
Light Period ◽  
Inert Gas ◽  
Quantum Yields ◽  
Volatile Product ◽  
Intermittent Illumination ◽  
Static Conditions

The reaction of isopropanol vapor with Hg 6(3P1) atoms has been investigated under static conditions at 25 °C under continuous and intermittent illumination. The effect of added inert gas and isolation of the 2537 Å Hg resonance line were also studied.The products of the reaction are H2 (0.72), CH3COCH3 (0.25), CO, CH4, C2H6, CH3CHO, and H2O, with the numbers in parentheses representing the quantum yields at zero exposure time. The non-volatile product remaining in the cell was a mixture of C6-glycols, containing 98.6% pinacol, 1.2% 2-methyl-2,4-pentanediol, and ca. 0.2% or less of 2,5-hexanediol.Under intermittent illumination, the quantum yield of hydrogen production, measured as a function of light period, tL, rose linearly with log tL, and had a constant value of unity for tL < 0.45 msec. A mechanism is proposed involving the primary formation with perfect efficiency of isopropoxy radicals and H atoms.

THE REACTION OF t-BUTYL ALCOHOL VAPOR WITH Hg 6(3P1) ATOMS

1963 ◽  
Vol 41 (11) ◽  
pp. 2849-2860 ◽  
Author(s):  
Arthur R. Knight ◽  
Harry E. Gunning
Keyword(s):  
Nitric Oxide ◽  
Butyl Alcohol ◽  
Continuous Illumination ◽  
Quantum Yields ◽  
Static System ◽  
Reaction Products ◽  
Subsequent Reaction ◽  
Alcohol Vapor ◽  
Intermittent Illumination ◽  
In Parenthesis

The nature of the decomposition of t-butyl alcohol vapor, photosensitized by Hg 6(3P1) atoms in a static system at room temperature, has been examined under a variety of conditions of continuous and intermittent illumination. The inhibiting effect of nitric oxide has also been studied, as well as the influence of added inert gas.In the decomposition of pure substrate, the reaction products, with the initial quantum yields, Φ°, under continuous illumination in parenthesis, were: H2 (0.045), Me2CO (0.090), CO (0), CH4 (0.015), C2H6 (0.030) together with lesser amounts of C3H8, Me3CH, Me3CMe, and Me3COMe. On addition of nitric oxide, Me3CONO, Me2CO, N2O, N2, H2O, and trace quantities of H2 and CO were the only products observed.The reaction[Formula: see text]is proposed as the primary process in the decomposition and kinetic evidence is presented that the initially formed t-butoxy radicals possess excess energy and that their principal subsequent reaction is unimolecular cleavage into acetone and methyl. The results furthermore indicate that the substrate itself is quite inert to abstractive attack by the primary radicals.

Photolysis (λ =185 nm) of Liquid Pivalaldehyde Dimethyl Aceta

1977 ◽  
Vol 32 (2) ◽  
pp. 209-212 ◽  
Author(s):  
Peter Naderwitz ◽  
Heinz-Peter Schuchmann ◽  
Clemens Von Sonntag
Keyword(s):  
Methyl Formate ◽  
Hydrogen Abstraction ◽  
Dimethyl Acetal ◽  
Quantum Yields ◽  
Formaldehyde Dimethyl Acetal

Deoxygenated liquid pivalaldehyde dimethyl acetal was photolyzed at λ = 185 nm, and 28 products have been determined. The major ones and their quantum yields are: methyl formate (0.47), isobutene (0.39), methane (0.28), neopentane (0.16), isobutane (0.13), formaldehyde dimethyl acetal (0.13), formaldehyde (0.09), methyl neopentyl ether (0.09), methanol (0.07), and methyl pivalate (0.04). The predominant primary photoprocesses are suggested to be the scission of the O–CH3 bond (homolytic, 0.51; molecular, 0.04) and the C-tBu bond (homolytic and molecular, 0.16). Minor processes are the scission of the C–OCH3 (molecular, 0.09; homolytic, 0.03), C–H (0.006), and C–CH3 bonds (&lt; 0.01). The radical (A) eliminates with ease t-butyl (reaction (i)). This process is at least 10 times more efficient than methoxy elimination or hydrogen abstraction from the substrate.[xxx]

scholarly journals Edge stabilization in reduced-dimensional perovskites

2020 ◽  
Vol 11 (1) ◽  
Author(s):  
Li Na Quan ◽  
Dongxin Ma ◽  
Yongbiao Zhao ◽  
Oleksandr Voznyy ◽  
Haifeng Yuan ◽  
...  
Keyword(s):  
Structural Diversity ◽  
Continuous Illumination ◽  
Quantum Yields ◽  
Color Purity ◽  
Phosphine Oxides ◽  
Maximum Luminance ◽  
Light Emitting ◽  
Tunable Bandgap ◽  
Luminescence Color ◽  
Oxidative Attack

AbstractReduced-dimensional perovskites are attractive light-emitting materials due to their efficient luminescence, color purity, tunable bandgap, and structural diversity. A major limitation in perovskite light-emitting diodes is their limited operational stability. Here we demonstrate that rapid photodegradation arises from edge-initiated photooxidation, wherein oxidative attack is powered by photogenerated and electrically-injected carriers that diffuse to the nanoplatelet edges and produce superoxide. We report an edge-stabilization strategy wherein phosphine oxides passivate unsaturated lead sites during perovskite crystallization. With this approach, we synthesize reduced-dimensional perovskites that exhibit 97 ± 3% photoluminescence quantum yields and stabilities that exceed 300 h upon continuous illumination in an air ambient. We achieve green-emitting devices with a peak external quantum efficiency (EQE) of 14% at 1000 cd m−2; their maximum luminance is 4.5 × 104 cd m−2 (corresponding to an EQE of 5%); and, at 4000 cd m−2, they achieve an operational half-lifetime of 3.5 h.

scholarly journals Specific Light-Emitting Diodes Can Suppress Sporulation of Podosphaera pannosa on Greenhouse Roses

Plant Disease ◽  
2010 ◽  
Vol 94 (9) ◽  
pp. 1105-1110 ◽  
Author(s):  
A. Suthaparan ◽  
S. Torre ◽  
A. Stensvand ◽  
M. L. Herrero ◽  
R. I. Pettersen ◽  
...  
Keyword(s):  
Wind Tunnel ◽  
White Light ◽  
Light Emitting Diodes ◽  
Dark Period ◽  
Red Light ◽  
Suppressive Effect ◽  
Continuous Illumination ◽  
Light Emitting ◽  
Dark Interval ◽  
Red Leds

When rose plants bearing colonies of Podosphaera pannosa were placed in a wind tunnel, the number of conidia trapped was directly proportional to intensity of daylight-balanced (white) light from 5 to 150 μmol m–2 s–1. Illumination of samples using blue (420 to 520 nm) light-emitting diodes (LEDs) increased the number of conidia trapped by a factor of approximately 2.7 over white light but germination of conidia under blue light was reduced by approximately 16.5% compared with conidia germination under white light. The number of conidia trapped under far-red (>685 nm) LEDs was approximately 4.7 times higher than in white light, and 13.3 times higher than under red (575 to 675 nm) LEDs, and germination was not induced compared with white light. When mildewed plants were exposed to cycles of 18 h of white light followed by 6 h of blue, red, far-red light, or darkness, light from the red LEDs reduced the number of conidia trapped by approximately 88% compared with darkness or far-red light. Interrupting the above dark period with 1 h of light from red LEDs also reduced the number of conidia trapped, while a 1-h period of light from far-red following the 1 h of light from red LEDs nullified the suppressive effect of red light. Our results indicate that brief exposure to red light during the dark interval may be as effective as continuous illumination in suppressing powdery mildew in greenhouse rose plant (Rosa × hybrida).

scholarly journals Modelling of quantum yields in photocatalytic membrane reactors immobilising titanium dioxide

2006 ◽  
Vol 2006 ◽  
pp. 1-8 ◽  
Author(s):  
Ignazio Renato Bellobono ◽  
Giulia de Martini ◽  
Paola Maria Tozzi ◽  
Carmen Canevali ◽  
Franca Morazzoni ◽  
...  
Keyword(s):  
Hydroxyl Radicals ◽  
Membrane Reactors ◽  
Quantum Yields ◽  
Peroxide Formation ◽  
Initial Concentration ◽  
A Value ◽  
Maximum Value ◽  
Radiant Power ◽  
Hydrogen Peroxide Formation ◽  
Kinetics Of

For some model molecules (methanoic and ethanoic acids, methane, and phenol), systematic investigations of quantum yields were carried out in the present paper, as a function of concentration and of absorbed radiant power. Quantum yieldsΦ∞, calculated from rates, followed an apparently Langmuirian function of initial concentrationC0, by whichΦ∞values at “infinite” concentration could be obtained. By having thus established that quantum yields of photomineralisationΦ∞are independent of radiation wavelength, within the absorption range of semiconductor, but depend on radiant power, such a dependency was experimentally investigated. For all the investigated molecules, the maximum allowable values reached in the low radiant power range clearly appeared as a plateau. On the contrary, at high radiant power values, another plateau, at a value of about 1/4-1/5 with respect to the maximum value, was evident. This was interpreted on the basis of a competition kinetics of hydroxyl radicals with themselves, leading to hydrogen peroxide formation, other than with substrate or intermediate molecules leading to full mineralisation. Modelling of quantum yields as a function of concentration and radiant power thus allows a fully consistent and trustworthy design of photoreactors.

Effect of benzimidazole and kinetin on the nicotinamide nucleotide content of senescing wheat leaves

1968 ◽  
Vol 46 (2) ◽  
pp. 167-178 ◽  
Author(s):  
D. Mishra ◽  
E. R. Waygood
Keyword(s):  
Dark Period ◽  
Mean Value ◽  
Continuous Illumination ◽  
Nad Kinase ◽  
Nonaqueous Media ◽  
Nucleotide Content ◽  
Significant Difference ◽  
Detached Leaves ◽  
Wheat Leaves ◽  
Photosynthetic Electron Transfer

Assays of nicotinamide nucleotides were made on detached leaves of wheat, Triticum dicoccum var. Khapli, immediately after excision and at the end of a 16-h photoperiod and 8-h dark period at 1, 3, and 5 days on leaves floated on water, and on benzimidazole, kinetin, or both. The total nicotinamide nucleotide content of 25 nmoles per gram fresh weight was increased by treatments with these kinins. A diurnal rhythm was observed in all treatments involving an increase of NADP(H) and a decrease of NAD(H) during the photoperiod, whereas the opposite was the case in darkness. The ratio NAD(H)/NADP(H) was about equimolar after excision and decreased to a mean value of 0.4 in all treatments after the first photoperiod. Thereafter, despite fluctuations in light and darkness and increased synthesis of NADPH in the treatments, the ratio increased to a mean value of 1.5 after 5 days, with no significant difference between treatments. The transformations in light can be explained by the combined operation of NAD kinase, NADH transhydrogenase, photosynthetic electron transfer forming NADPH, and biosynthetic reductive reactions restoring NADP.Assays were also made on chloroplasts isolated in nonaqueous media from leaves treated similarly but under continuous illumination. The NAD content of chloroplasts was 11.2 nmoles per μmole chlorophyll as compared to 3.14 for NADP. The oxidized nucleotides predominated in chloroplasts. Chloroplasts from leaves floated on water had lost all their NADP after 6 days, whereas those treated with benzimidazole or kinetin increased or maintained their level of NADP. The evidence is discussed with reference to the mechanism of action of benzimidazole and kinetin in delaying the onset of visible and metabolic changes that occur during the senescence of wheat leaves.

scholarly journals Structural Causes of Singlet/triplet Preferences of Norrish Type II Reactions in Carbonyls

2020 ◽  
Author(s):  
Keiran Rowell ◽  
Scott Kable ◽  
Meredith J. T. Jordan
Keyword(s):  
Hydrogen Abstraction ◽  
Conical Intersection ◽  
Quantum Yields ◽  
Type Ii ◽  
Structure Activity ◽  
Abstraction Reaction ◽  
Norrish Type ◽  
Close Proximity ◽  
Unsaturated Carbonyls ◽  
Hydrogen Abstraction Reaction

Photolysis thresholds are calculated for the Norrish Type II (NTII) intramolecular γ-hydrogen abstraction reaction in 22 structurally informative carbonyl species. The B2GP-PLYP excited state <i>S</i><sub>1</sub> and <i>T</i><sub>1</sub> thresholds agree well with triplet quenching experiments. However, many linear-response methods deliver poor <i>S</i><sub>1</sub> energetics, which is explained by a <i>S</i><sub>1</sub>/<i>S</i><sub>0</sub> conical intersection in close proximity to the <i>S</i><sub>1 </sub>transition state. Multiconfigurational CASSCF calculations confirm a conical intersection features across all carbonyl classes. <div><br></div><div>Structure–activity relationships are determined that could be used in atmospheric carbonyl photochemsitry modelling. This is exemplified for butanal, whose NTII quantum yields are too low when used as a ‘surrogate’ for larger carbonyls, since butanal lacks the γ-substitution that stabilises the 1,4- biradical. Reaction on <i>T</i><sub>1</sub> dominates only in species where the <i>S</i><sub>1</sub> thresholds are high — typically ketones. The α, β-unsaturated carbonyls cannot cleave the α–β bond, causing them to photoisomerise. A concerted <i>S</i><sub>0</sub> NTII mechanism is calculated to be viable and may explain the recent detection of NTII photoproducts in the photolysis of pentan-2-one below the <i>T</i><sub>1</sub> threshold.</div>

scholarly journals Structural Causes of Singlet/triplet Preferences of Norrish Type II Reactions in Carbonyls

2020 ◽  
Author(s):  
Keiran Rowell ◽  
Scott Kable ◽  
Meredith J. T. Jordan
Keyword(s):  
Hydrogen Abstraction ◽  
Conical Intersection ◽  
Quantum Yields ◽  
Type Ii ◽  
Structure Activity ◽  
Abstraction Reaction ◽  
Norrish Type ◽  
Close Proximity ◽  
Unsaturated Carbonyls ◽  
Hydrogen Abstraction Reaction

Photolysis thresholds are calculated for the Norrish Type II (NTII) intramolecular γ-hydrogen abstraction reaction in 22 structurally informative carbonyl species. The B2GP-PLYP excited state <i>S</i><sub>1</sub> and <i>T</i><sub>1</sub> thresholds agree well with triplet quenching experiments. However, many linear-response methods deliver poor <i>S</i><sub>1</sub> energetics, which is explained by a <i>S</i><sub>1</sub>/<i>S</i><sub>0</sub> conical intersection in close proximity to the <i>S</i><sub>1 </sub>transition state. Multiconfigurational CASSCF calculations confirm a conical intersection features across all carbonyl classes. <div><br></div><div>Structure–activity relationships are determined that could be used in atmospheric carbonyl photochemsitry modelling. This is exemplified for butanal, whose NTII quantum yields are too low when used as a ‘surrogate’ for larger carbonyls, since butanal lacks the γ-substitution that stabilises the 1,4- biradical. Reaction on <i>T</i><sub>1</sub> dominates only in species where the <i>S</i><sub>1</sub> thresholds are high — typically ketones. The α, β-unsaturated carbonyls cannot cleave the α–β bond, causing them to photoisomerise. A concerted <i>S</i><sub>0</sub> NTII mechanism is calculated to be viable and may explain the recent detection of NTII photoproducts in the photolysis of pentan-2-one below the <i>T</i><sub>1</sub> threshold.</div>

Direct Photolysis of 2-Propanol Vapor

1972 ◽  
Vol 50 (14) ◽  
pp. 2217-2223 ◽  
Author(s):  
O. S. Herasymowych ◽  
A. R. Knight
Keyword(s):  
Quantum Yield ◽  
Wavelength Range ◽  
Exposure Time ◽  
Yield Enhancement ◽  
Quantum Yields ◽  
Unimolecular Decomposition ◽  
Direct Photolysis ◽  
Volatile Products ◽  
Temperature And Pressure

The photolysis of 2-propanol vapor in the 1800–2000 Å wavelength range has been investigated. The volatile products of the reaction and their quantum yields at 80 °C and 200 Torr substrate pressure are H2 (0.64), CH3COCH3 (0.34), CH4 (0.39), CH3CHO (0.29), CO (0.15), and C2H6 (0.08). A mechanism is proposed that accounts for the observed rate variations with substrate pressure, exposure time, temperature, and pressure of inert addend. Acetone and acetaldehyde undergo significant secondary decomposition and this is the source of CO, CH4, and C2H6. Acetaldehyde is formed in the unimolecular decomposition of C3H7O radicals produced in the primary process.The effects of CO2 and CF4 as inert addends have been examined and it has been established that the quantum yield enhancement through collision induced predissociation that has been reported to occur in methanol is not a characteristic of the 2-propanol photolysis.

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