scholarly journals PRIMARY QUANTUM EFFICIENCIES IN THE REACTION OF CYCLOPENTANE WITH MERCURY 6(3P1) ATOMS

1960 ◽  
Vol 38 (12) ◽  
pp. 2295-2302 ◽  
Author(s):  
Richard L. Stock ◽  
Harry E. Gunning
Keyword(s):  
Nitric Oxide ◽  
Steady State ◽  
Quantum Yield ◽  
Prolonged Exposure ◽  
Product Formation ◽  
Quantum Yields ◽  
Gas Liquid Chromatography ◽  
Low Light ◽  
Yield Data ◽  
Static Conditions

An investigation has been made of the reaction of cyclopentane with Hg 6(3P1) atoms at a substrate pressure of 107 mm, under static conditions at 24 °C. Low light intensities were used in order to minimize secondary reactions.The products of the reaction, for small extents of decomposition, have been shown to be exclusively hydrogen, bicyclopentyl, and cyclopentene. With increasing duration of exposure, the cyclopentene-to-cyclopentane ratio achieves a steady-state value of 5.7 × 10−3. Furthermore, it has been found that the same ratio is ultimately reached, upon prolonged exposure of a substrate initially containing cyclopentene at a concentration higher than the steady-state value. In the runs with added cyclopentene, a fourth product appeared in measurable quantities. Its molecular weight corresponded to the formula, C10H16, and it was assumed to be a cyclopentyl cyclopentene. The same compound appears in extensive decomposition of the pure substrate.The addition of small amounts of nitric oxide was found to have a marked inhibiting effect on the reaction. Bicyclopentyl formation was completely suppressed when 0.7 mole% of nitric oxide was present; and the cyclopentene yield was reduced to one-fifth of its value for the pure substrate, by adding 0.98 mole% of nitric oxide.In order to obtain primary quantum yields for the reaction, a series of runs were performed of 1 to 33 minutes in duration, with a cyclopentane which had been purified by gas–liquid chromatography. By a short extrapolation of the mean quantum yields of product formation to zero extent of reaction, it was found that the primary quantum yields for hydrogen, bicyclopentyl, and cyclopentene were respectively 0.8, 0.4, and 0.4.On the basis of a simple four-step paraffinic mechanism, taken in conjunction with the primary quantum yield data, it is concluded that the reaction has a primary quantum yield of substrate decomposition of 0.8, and that cyclopentyl radicals have the same rates for disproportionation and recombination at 24 °C.

Terminology, relative photonic efficiencies and quantum yields in heterogeneous photocatalysis. Part II: Experimental determination of quantum yields

1999 ◽  
Vol 71 (2) ◽  
pp. 321-335 ◽  
Author(s):  
Angela Salinaro ◽  
Alexei V. Emeline ◽  
Jincai Zhao ◽  
Hisao Hidaka ◽  
Vladimir K. Ryabchuk ◽  
...  
Keyword(s):  
Quantum Yield ◽  
Visible Region ◽  
Heterogeneous Photocatalysis ◽  
Quantum Yields ◽  
Yield Data ◽  
Normal Absorption ◽  
The One ◽  
Solid Liquid ◽  
Photonic Efficiency

In the preceding article [Serpone and Salinaro, Pure Appl. Chem., 71(2), 303-320 (1999)] we examined two principal features of heterogeneous photocatalysis that demanded scrutiny: (i) description of photocatalysis and (ii) description of process efficiencies. For the latter we proposed a protocol relative photonic efficiency which could subsequently be converted to quantum yields. A difficulty in expressing a quantum yield in heterogeneous photochemistry is the very nature of the system, either solid/liquid or solid/gas, which places severe restrictions on measurement of the photon flow absorbed by the light harvesting component, herein the photocatalyst TiO2, owing to non-negligible scattering by the particulates. It was imperative therefore to examine the extent of this problem. Extinction and absorption spectra of TiO2 dispersions were determined at low titania loadings by normal absorption spectroscopy and by an integrated sphere method, respectively, to assess the extent of light scattering. The method is compared to the one reported by Grela et al. [J. Phys. Chem., 100, 16940 (1996)] who used a polynomial extrapolation of the light scattered in the visible region into the UV region where TiO2 absorbs significantly. This extrapolation underestimates the scattering component present in the extinction spectra, and will no doubt affect the accuracy of the quantum yield data. Further, we report additional details in assessing limiting photonic efficiencies and quantum yields in heterogeneous photocatalysis.

Absorption and utilization of radiant energy by light- and shade-adapted colonies of the hermatypic coral Stylophora pistillata

1984 ◽  
Vol 222 (1227) ◽  
pp. 203-214 ◽  
Keyword(s):  
Quantum Yield ◽  
Absorption Coefficient ◽  
Red Sea ◽  
Radiant Energy ◽  
Quantum Yields ◽  
Hermatypic Coral ◽  
Specific Absorption Coefficient ◽  
Low Light ◽  
Stylophora Pistillata ◽  
Photosynthetic Rates

The specific absorption coefficient for chlorophyll a ( k c ) was measured in zooxanthellae from light- and shade-adapted colonies of the hermatypic coral, Stylophora pistillata from the Red Sea. These data, together with measurements of photosynthetic rates and irradiance, were used to compare the quantum yields of photosynthesis in these corals. Quantum yields varied from 0.10 CO 2 per quantum at low light to less than 0.001 CO 2 per quantum at maximal irradiances. Shade-adapted corals had higher pigment content, which allowed them to have twice as much light harvesting capability as light-adapted corals. In all cases, however, the quantum yield of the light-adapted corals was higher by a factor of about 1.5.

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 Hg 6(3P1)-PHOTOSENSITIZED DECOMPOSITION OF NITRIC OXIDE

1961 ◽  
Vol 39 (12) ◽  
pp. 2549-2555 ◽  
Author(s):  
Otto P. Strausz ◽  
Harry E. Gunning
Keyword(s):  
Nitric Oxide ◽  
Quantum Yield ◽  
Ground State ◽  
Pressure Range ◽  
Oxides Of Nitrogen ◽  
Total Rate ◽  
A Value ◽  
Electronically Excited ◽  
Static Conditions ◽  
Observed Behavior

The reaction of NO with Hg 6(3P1) atoms has been studied under static conditions at 30°, over the pressure range 1–286 mm. The products were found to be N2, N2O, and higher oxides of nitrogen. At NO pressures exceeding 4 mm, the total rate of formation of N2+N2O was constant, while the ratio N2O/N2 increased linearly with the substrate pressure. The rate was found to vary directly with the first power of the intensity at 2537 Å, and a value of 1.9 × 10−3 moles/einstein was established for the quantum yield of N2 + N2O production. In the proposed mechanism, reaction is attributed to the decomposition of an energy-rich dimer, (NO)2*, which is formed by the collision of electronically excited (4II) NO molecules with those in the ground state. The (NO)2* species is assumed to decompose by the steps: (NO)2* → N2 + O2 and (NO)2* + NO → N2O + NO2. The mechanism satisfactorily explains the observed behavior of the system.

scholarly journals Native hemiparasite and light effects on photoprotection and photodamage in a native host

2015 ◽  
Vol 42 (12) ◽  
pp. 1168 ◽  
Author(s):  
Robert M. Cirocco ◽  
Melinda J. Waterman ◽  
Sharon A. Robinson ◽  
José M. Facelli ◽  
Jennifer R. Watling
Keyword(s):  
Quantum Yield ◽  
Xanthophyll Cycle ◽  
Pigment Content ◽  
Host Susceptibility ◽  
Quantum Yields ◽  
Chlorophyll B ◽  
Low Light ◽  
Light Effects ◽  
Pigment Concentrations ◽  
Native Host

Plants infected with hemiparasites often have lowered rates of photosynthesis, which could make them more susceptible to photodamage. However, it is also possible that infected plants increase their photoprotective capacity by changing their pigment content and/or engagement of the xanthophyll cycle. There are no published studies investigating infection effects on host pigment dynamics and how this relates to host susceptibility to photodamage whether in high (HL) or low light (LL). A glasshouse experiment was conducted where Leptospermum myrsinoides Schltdl. either uninfected or infected with Cassytha pubescens R.Br. was grown in HL or LL and pigment content of both host and parasite were assessed. Infection with C. pubescens significantly decreased all foliar pigment concentrations (except chlorophyll b) in L. myrsinoides in both HL and LL. Xanthophyll cycle (violaxanthin, antheraxanthin, zeaxanthin; VAZ) and chlorophyll (Chl) pigments decreased in parallel in response to infection, hence, VAZ/Chl of the host was unaffected by C. pubescens in either HL or LL. Pre-dawn and midday de-epoxidation state [(A + Z)/(V + A + Z)] of L. myrsinoides was also unaffected by infection in both HL and LL. Thus, L. myrsinoides infected with C. pubescens maintained similar photoprotective capacity per unit chlorophyll and engagement of the xanthophyll cycle as uninfected plants. Even though midday quantum yield (ΦPSII) of HL plants was affected by infection, pre-dawn maximum quantum yields (Fv/Fm) of hosts were the same as uninfected plants whether in HL or LL. This ability of L. myrsinoides to maintain photoprotective capacity/engagement when infected by C. pubescens thereby preventing photodamage could explain this host’s tolerance to hemiparasite infection.

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.

Shear stress-induced vasodilation in porcine coronary conduit arteries is independent of nitric oxide release

2001 ◽  
Vol 280 (6) ◽  
pp. H2581-H2590 ◽  
Author(s):  
Sandeep Dube ◽  
John M. Canty
Keyword(s):  
Nitric Oxide ◽  
Shear Stress ◽  
Smooth Muscle ◽  
Steady State ◽  
Vascular Smooth Muscle ◽  
Coronary Arteries ◽  
State Changes ◽  
Static Conditions ◽  
Flow Mediated Vasodilation ◽  
Nonpulsatile Flow

The present study was performed to determine the importance of nitric oxide in eliciting epicardial coronary artery dilation during sustained increases in shear stress in the absence of pulsatile flow. Isolated first-order porcine epicardial coronary conduit arteries (∼500 μm) were preconstricted (U-46619) and subjected to steady-state changes in flow in vitro. Nonpulsatile flow (shear stress range from 0 to ∼100 dyn/cm2) produced a graded dilation of epicardial arteries. Inhibiting nitric oxide synthase with 10−5 M N ω-nitro-l-arginine methyl ester (l-NAME) blocked bradykinin-induced vasodilation but did not affect the flow-diameter relation or the maximum change in diameter from static conditions (67 ± 10 μm in control vs. 71 ± 8 μm after l-NAME, P = not significant). The addition of indomethacin (10−5 M) had no effect on flow-mediated vasodilation. Depolarizing vascular smooth muscle with KCl (60 mM) or removing the endothelium blocked bradykinin vasodilation and completely abolished flow-mediated responses. The K+channel blocker tetraethylammonium chloride (TEA; 10−4M) attenuated flow-mediated vasodilation (maximum diameter change was 110 ± 18 μm under control conditions vs. 58 ± 10 μm after TEA, P < 0.001). These data indicate that epicardial coronary arteries dilate to steady-state changes in nonpulsatile flow via a mechanism that is independent of nitric oxide production. The ability to completely block this with KCl and attenuate it with TEA supports the hypothesis that epicardial coronary arteries dilate to steady levels of shear stress through hyperpolarization of vascular smooth muscle. This may be secondary to the release of an endothelium-dependent hyperpolarizing factor.

scholarly journals Constraint-based modelling revealed changes in metabolic flux modes associated with the Kok effect

2020 ◽  
Author(s):  
Wei Qiang Ong ◽  
C. Y. Maurice Cheung
Keyword(s):  
Quantum Yield ◽  
Light Intensity ◽  
Energy Demand ◽  
Metabolic Flux ◽  
Net Photosynthesis ◽  
Quantum Yields ◽  
Energetic Efficiency ◽  
Low Light ◽  
Subtle Change ◽  
Low Light Intensity

AbstractConstraint-based modelling was applied to provide a mechanistic understanding of the possible metabolic origins of the ‘Kok effect’ – the change in quantum yield of net photosynthesis at low light intensity. The well-known change in quantum yield near the light-compensation point (LCP) was predicted as an emergent behaviour from a purely stoichiometric model. From our modelling results, we discovered another subtle change in quantum yield at a light intensity lower than the LCP. Our model predicted a series of changes in metabolic flux modes in central carbon metabolism associated with the changes in quantum yields. We demonstrated that the Kok effect can be explained by changes in metabolic flux modes between catabolism and photorespiration. Changes in RuBisCO carboxylation to oxygenation ratio resulted in a change in quantum yield at light intensities above the LCP, but not below the LCP, indicating the role of photorespiration in producing the Kok effect. Cellular energy demand was predicted to have no impact on the quantum yield. Our model showed that the Kok method vastly overestimates day respiration – the CO2 released by non-photorespiratory processes in illuminated leaves. The theoretical maximum quantum yield at low light intensity was higher than typical measured values, suggesting that leaf metabolism at low light may not be regulated to optimise for energetic efficiency. Our model predictions gave insights into the set of energetically optimal changes in flux modes in low light as light intensity increases from darkness.One sentence summaryThe Kok effect can be explained by the changes in flux modes between catabolism and photorespiration.

The photocycloaddition of naphthoates with acetylacetone; dramatic acid promotions of product quantum yields

1991 ◽  
Vol 69 (8) ◽  
pp. 1261-1272 ◽  
Author(s):  
Yuan L. Chow ◽  
Xiao-Yun Liu
Keyword(s):  
Quantum Yield ◽  
Methyl Iodide ◽  
Acid Catalysis ◽  
Product Formation ◽  
Quantum Yields ◽  
Reactive Intermediate ◽  
Excited Species ◽  
Order Of Magnitude ◽  
Cyclobutane Derivatives ◽  
Volmer Constant

In acetonitrile and methanol, methyl 1- and methyl 2-naphthoate (1- and 2-NpCO2CH3) underwent [2 + 2] photocycloaddition with acetylacetone (acacH) from a reactive species derived from the lowest spectroscopic singlet excited state to give cyclobutane derivatives such as 9 that ring-opened to afford addition products of acetyl and acetonyl moieties at the 7,8-position for 1-NpCO2CH3 (2 and 3) and the 1,2-position for 2-NpCO2CH3 (7). Further irradiation of 3 and 7 caused a deep-seated rearrangement of 3 to give 4 and an intramolecular addition of 7 to give the caged product 8. The photocycloaddition quantum yields were increased remarkably in the presence of a trace amount (< 0.001 M) of protic acids. For example, the limiting quantum yield of 2 and 3 with Фadducts = 0.033 (in the absence) increased to Фadducts > 0.5 under comparable conditions in the presence of [H2SO4] = 0.001 M, approaching the maximum asymptotically at about this concentration; the increases of the quantum yield could not be correlated with H2SO4 concentrations. The acid promotion of the product formation elevated the photocycloaddition to a significantly useful preparative reaction. The photocycloaddition of 2-NpCO2CH3 was quenched by tributylamine, dimethylaniline, and methyl iodide, and could not be initiated by typical triplet sensitization. Strong fluorescence of 2-NpCO2CH3 at 358 nm in CH3CN was quenched by acetylacetone, tributylamine, dimethylaniline, and methyl iodide, the last of which concurrently enhanced the phosphorescence intensity of 2-NpCO2CH3. In the presence of [H2SO4] > 0.005 M the fluorescence intensity at 358 nm was quenched and a new fluorescence at 470 nm corresponding to protonated 12-NpCO2CH3 appeared. However, in the [H2SO4] < 0.002 M region, the new fluorescence was not observed, indicating that the protonation scarcely occurred. The Stern–Volmer constant, obtained by the quantum yield monitor, of the 2-NpCO2CH3 photocycloaddition with acacH was more than an order of magnitude smaller than that obtained by the quenching of 2-NpCO2CH3 fluorescence by acacH. The discrepancies outlined above clearly demonstrate that the reactive intermediate of the photocycloaddition is not the exciplex of the spectroscopic singlet excited species of 12-NpCO2CH3 and acacH, but one that is derived from the exciplex. It is speculated that this unknown reactive intermediate interacts with a proton to promote the photocycloaddition. Key words: photocycloaddition of naphthoates, photorearrangement of styryl ketones, acid catalysis of quantum yields, fluorescence of protonated naphthoates, acid enhancement of singlet quenching.

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