THE QUANTUM YIELD IN THE PHOTOCHEMICAL DECOMPOSITION OF NITROGEN DIOXIDE

1928 ◽  
Vol 50 (3) ◽  
pp. 774-782 ◽  
Author(s):  
Roscoe G. Dickinson ◽  
Warren P. Baxter
Keyword(s):  
Quantum Yield ◽  
Nitrogen Dioxide ◽  
Photochemical Decomposition

The photochemical and thermal decompositions of hydrogen sulphide

1953 ◽  
Vol 216 (1126) ◽  
pp. 344-361 ◽  
Keyword(s):  
Thermal Decomposition ◽  
Quantum Yield ◽  
Hydrogen Sulphide ◽  
Low Temperatures ◽  
Room Temperature ◽  
Large Fraction ◽  
Kcal Mole ◽  
Hydrogen Atoms ◽  
Photochemical Decomposition ◽  
Bimolecular Mechanism

The photochemical decomposition of hydrogen sulphide has been investigated at pressures between 8 and 550 mm of mercury and at temperatures between 27 and 650° C, using the narrow cadmium line ( λ 2288) and the broad mercury band (about λ 2550). At room temperature the quantum yield increases with pressure from 1.09 at 30 mm to 1.26 at 200 mm. Above 200 mm pressure there was no further increase in the quantum yield. Temperature had little effect on the quantum yield at λ 2550, but there was a marked increase in the rate of hydrogen production between 500 and 650° C with 2288 Å radiation. This may have been caused by the decomposition of excited hydrosulphide radicals. The results are consistent with a mechanism involving hydrogen atoms and hydrosulphide radicals. The mercury-photosensitized reaction is less efficient than the photochemical decomposition, the quantum yield being only about 0.45. The efficiency increased with temperature and approached unity at high temperatures and pressures. This agrees with the suggestion that a large fraction of the quenching collisions lead to the formation of Hg ( 3 P 0 ) atoms. The thermal decomposition is heterogeneous at low temperatures and becomes homogeneous and of the second order at 650° C. The experimental evidence suggests the bimolecular mechanism 2H 2 S → 2H 2 + S 2 . The activation energies are 25 kcal/mole (heterogeneous) and 50 kcal/mole (homogeneous).

CONDITIONS FOR THE PHOTOCHEMICAL NITRATION OF BENZENE

1965 ◽  
Vol 43 (6) ◽  
pp. 1714-1719 ◽  
Author(s):  
David L. Bunbury
Keyword(s):  
Liquid Phase ◽  
Quantum Yield ◽  
Nitrogen Dioxide ◽  
Gas Phase ◽  
Dark Reaction ◽  
Gas Phases

The reaction of benzene and nitrogen dioxide to produce nitrobenzene has been studied in the liquid and gas phases, in the dark, and with irradiation by light of 439 mμ and of 366 mμ. The concentration of NO2 in the liquid was varied from 0.08 to 1.6 moles/1 and in the gas from 0.0035 to 0.053 moles/1. No nitrobenzene was produced under any conditions in the liquid phase. Nitrobenzene is produced in the gas phase at high NO2 concentrations with irradiation by 366 mμ light. The quantum yield is 0.2. At 439 mμ the quantum yield is not more than 0.02. There is a very small dark reaction. As the concentration of NO2 in the gas is reduced the yield of nitrobenzene falls off very rapidly and is zero at the lowest concentration used, both in dark and light.

scholarly journals Determination of Quantum Yield for the Photochemical Decomposition of Dichloramine-B and Dibromamine-B in Aqueous Acetic Acid Medium

2007 ◽  
Vol 4 (4) ◽  
pp. 502-509
Author(s):  
K. N. Mohana ◽  
N. Prasad ◽  
P. M. Ramadas Bhandarkar
Keyword(s):  
Acetic Acid ◽  
Quantum Yield ◽  
Uv Light ◽  
Incident Light ◽  
Aqueous Acetic Acid ◽  
Acetic Acid Medium ◽  
Rate Law ◽  
Photochemical Decomposition ◽  
Photolytic Decomposition

The photolysis of dihaloamines (RNX2),viz., dichloramine-B (DCB) and dibromamine-B (DBB) in aqueous acetic acid (1:1 v/v) solutions has been studied with the UV light source (λ= 2537 Å). The experimental rate law obtained is - d [RNX2] / dt = k' Io/ [RNX2], where Iois the intensity of incident light. The addition of benzenesulphonamide, the product of photolysis or uranyl ion had no significant effect on the rate of photochemical decomposition. A slight decrease in the rate has been observed by the addition of NaCl / NaBr to DCB / DBB solutions. The quantum yield (Φ) for the photolytic decomposition has been computed. A suitable photolytic mechanism and a rate law consistent with the observed results have been proposed.

THE PHOTOCHEMICAL DECOMPOSITION OF METHYL AZIDE

1963 ◽  
Vol 41 (6) ◽  
pp. 1552-1559 ◽  
Author(s):  
C. L. Currie ◽  
B. deB. Darwent
Keyword(s):  
Quantum Yield ◽  
Vapor Phase ◽  
Gaseous Product ◽  
Short Chain ◽  
Excited Species ◽  
Photochemical Decomposition

The photolysis of methyl azide has been investigated in the vapor phase at low conversions and over suitable ranges of pressure, temperature, intensity, and wavelength. Under all conditions the principal gaseous product was N2 with small amounts of H2 (5–11%), and traces of CH4, C2H4, and C2H6. A condensate identified as (CH3N)x was also found.The quantum yield for the production of N2 is approximately 2, independent of intensity (over a 45-fold range), temperature (17–100 °C), and pressure (14–300 mm Hg). The quantum yield decreases slightly with increasing wavelength. Experiments with added CO2, CH3N2CH3, and C2H4 indicate the presence of a short chain carried mainly by the CH3N radical. Excited species probably play some role in the reaction.

The photolysis of ozone by ultraviolet radiation. I. The photolysis of pure, dry ozone

1965 ◽  
Vol 288 (1413) ◽  
pp. 200-211 ◽  
Keyword(s):  
Reaction Mechanism ◽  
Quantum Yield ◽  
Light Intensity ◽  
Ultraviolet Radiation ◽  
Oxygen Molecule ◽  
Inert Gases ◽  
Ozone Variation ◽  
Photochemical Decomposition ◽  
A Chain ◽  
Limiting Value

The photochemical decomposition of dry ozone has been studied at λ = 2537 Å. The quantum yield for the photolysis of pure ozone was proportional to the pressure of ozone; the highest quantum yield recorded was 16.7 at a pressure of 5 cmHg ozone. Variation of light intensity did not markedly affect the quantum yield, and some evidence was found for a wall termination reaction. A reaction mechanism is proposed in which O( 1 D ) atoms, formed in the primary photolysis, initiate a chain propagated by energy-rich oxygen molecules. A discussion of the nature of the energy-rich molecules is presented. Addition of inert gases to the pure ozone reduces the quantum yield to a limiting value of two. This is explained in terms of the deactivation of the energy-rich oxygen molecule. In the presence of oxygen, the quantum yield tends to zero, as a result of the reverse reaction O + O 2 + M → O 3 + M .

The photochemical decomposition of t -butyl hydroperoxide in solution

1953 ◽  
Vol 220 (1142) ◽  
pp. 322-339 ◽  
Keyword(s):  
Quantum Yield ◽  
Wave Length ◽  
Butyl Alcohol ◽  
Quantum Yields ◽  
Oxidation Reactions ◽  
Butyl Hydroperoxide ◽  
Acetone Water ◽  
Photochemical Decomposition ◽  
Solvent Molecules ◽  
A Chain

The photochemical decomposition of t -butyl hydroperoxide by light of wave-length 3130 Å has been investigated in three solvents. Reaction mechanisms are elucidated by consideration of the products and the quantum yields of decomposition. In carbon tetrachloride a chain reaction occurs in which the quantum yield of 3.2 at 20° C increases to 5.3 at 50° C. The main products are t -butyl alcohol and oxygen with smaller amounts of acetone, water and compounds arising from the oxidation of methyl radicals. The same series of reactions takes place in n -hexane, but superimposed are oxidation reactions involving solvent molecules which ultimately lead to the formation of alcohols. The quantum yield in this solvent is 3.9 and independent of temperature. When the peroxide is irradiated in dioxan solution immediate hydrogenation of the radicals produced in the primary photo-chemical act prevents the formation of reaction chains and the quantum yield is unity. The interaction of the radicals with solvent molecules is such that some of the etheric oxygen of the dioxan is transformed into alcoholic hydroxyl during the course of the reaction, and the fragmentation of dioxan gives formaldehyde Experiments with a dioxan solution using light of wave-length 2450 to 2800 Å show no fundamental change in the mode of decomposition of the peroxide, but an increase in concentration of the products of dioxan decomposition indicates a more vigorous attack by the radicals on the solvent.

Spectroscopic studies of the hydrogen-oxygen explosion initiated by the flash photolysis of nitrogen dioxide

1952 ◽  
Vol 210 (1103) ◽  
pp. 439-460 ◽  
Keyword(s):  
Nitrogen Dioxide ◽  
Flash Photolysis ◽  
Spectroscopic Studies ◽  
Reaction Scheme ◽  
Oh Radical ◽  
Time Intervals ◽  
Induction Periods ◽  
Photochemical Decomposition ◽  
Explosive Reaction ◽  
Flash Spectroscopy

The method of flash photolysis has been used to initiate the reaction between hydrogen and oxygen, using a small amount of nitrogen dioxide as sensitizer. The dependence of the ignition limits on total pressure, capacity and the pressure of nitrogen dioxide have been studied, as well as the flash photochemical decomposition of nitrogen dioxide alone. The explosive reaction is complete in a few milliseconds, and very short induction periods are found whose duration can be explained in terms of the initial temperature rise. It is shown that the initiation of the explosion in this way is reproducible to less than 10 -4 s and flash spectroscopy is used to study the development of the reactions with time. The spectra obtained are described and the reactions of the OH radical are investigated by means of its absorption spectrum , whose intensity variations with partial pressure of hydrogen, oxygen, nitrogen and water vapour over time intervals of 0·2 ms throughout the reaction are given. Addition of hydrogen accelerates the reaction, but oxygen in excess has the same effect as an inert gas which is to decrease the rate. It is shown that the important propagation steps are exclusively bimolecular and the main reactions of the OH radical are identified. The mechanism of the overall explosion reaction is discussed and a reaction scheme is given which is in accordance with the results.

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