Journal Articles (before-1995)
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Item Photochemistry of Michler’s Ketone in Cyclohexane and Alcohol Solvents(Journal of the Chemical Society : Faraday Transaction - I. The Chemical Society, London. 1977, 73 (10), 1977) Brown, Robert G; Porter, Sir GeorgeThe triplet lifetime of Michler's ketone has been measured in cyclohexane, isopropanol and ethanol and has been found to vary only slightly between solvents. In the light of these results, the photoreactivity of the ketone is interpreted as arising from population of an excited 3nπ* state from a lower-lying 3charge-transfer state.Item Interaction of Duroquinone Lowest Triplet with Amines(Journal of the Chemical Society : Faraday Transaction - I. The Chemical Society, London. 1977, 73 (10), 1977) Amouyal, Edmond; Bensasson, ReneThe reaction of the lowest triplet of duroquinone, 3Q, with tertiary amines (triethylamine TEA, diethylaniline DEA, triphenylamine TPA) has been investigated by laser flash absorption spectroscopy in non-polar (cyclohexane or benzene) and polar (acetonitrile) solvents. Three pathways of 3Q deactivation involving an exciplex as intermediate were observed: (i) an electron transfer to 3Q from TPA and DEA in a polar solvent, (ii) a H atom transfer to 3Q from DEA in a non-polar solvent and from TEA in a non-polar or a polar solvent, (iii) a physical quenching of 3Q by TPA in a non-polar solvent with no photoreduction products.Item Photochemistry and radiation chemistry of 9,10-anthraquinone-2-sodium sulphonate in aqueous solution. Part 3.—Pulse and gamma radiolysis(Journal of the Chemical Society : Faraday Transaction - I. The Chemical Society, London. 1977, 73 (05), 1977) Clark, K. P.; Stonehill, H. I.Electron-pulse and gamma radiolysis of “aqueous” solutions of the title compound (D) in the range pH 14 to > 100 % H2SO4 give the same products as photolysis (mainly α- and β-monohydroxyderivatives ROH with some polyhydroxylated D, and in the absence of oxygen, semiquinone and quinol), and the same variation with pH or acidity of the α : β ROH isomer ratio. Of the following rate constants (all in dm3 mol–1 s–1) the first three were determined by pulse radiolysis, the others by scavenger competition during gamma radiolysis : 2 DOH˙→ DHOH + ROH, 2 k=(1.41 ± 0.17)× 109; DOH˙+ O2→ DOH˙ O2., k=(1.39 ± 0.17)× 107; 2 D–˙→ D + D2–, 2 k=(1.33 ± 0.18)× 109; D + OH·→ DOH·, k=(2.68 ± 0.25)× 109; D + O·–→ DO·–, k= 6.1 × 107; D + O.–→ products other than DO.–, k= 1.63 × 108[this reaction is postulated to explain the fall in G(ROH) at pH > 12]. The effect of individual scavengers and of high alkalinity on the yield of ROH is different in photolysis and radiolysis. This suggests that since OH· is known to be the precursor of DOH· in radiolysis, any photolysis mechanism involving intermediate free OH· production is invalid.Item Radiation Chemistry and Photochemistry of Oxychlorine Ions: Part 2.—Photodecomposition of Aqueous Solutions of Hypochlorite Ions(Journal of the Chemical Society : Faraday Transaction - I. The Chemical Society, London. 1972, 68 (5), 1972) Buxton, G. V.; Subhani, M. S.The photodecomposition of alkaline aqueous solutions of hypochlorite ion has been investigated using steady state and flash photolysis techniques. At 365 nm the primary products are O(3P), O–, Cl and Cl– formed by the following processes [graphic omitted] with ϕa= 0.28 ± 0.03 and ϕb= 0.08 ± 0.02. At 313 nm and 253.7 nm O(1D) is also produced ClO–→ Cl + O(1D)(c) and the quantum yields are ϕa= 0.075 ± 0.015, ϕb= 0.127 ± 0.014, ϕc= 0.020 ± 0.015 at 313 nm, and ϕa= 0.074 ± 0.019, ϕb= 0.278 ± 0.016, ϕc= 0.133 ± 0.017 at 253.7 nm. The relative rates of reaction of O(3P) with O2, ClO– and ClO–2 have been found to be in the ratios 1 : 2.8 : 15.9. O(3P) reacts with ClO– and ClO–2 by abstraction of O as well as by addition. A complete reaction mechanism for the photodecomposition of ClO– is proposed.Item Radiation Chemistry and Photochemistry of Oxychlorine Ions: Part 1.—Radiolysis of Aqueous Solutions of Hypochlorite and Chlorite Ions(Journal of the Chemical Society : Faraday Transaction - I. The Chemical Society, London. 1972, 68 (5), 1972) Buxton, G. V.; Subhani, M. S.The radiolysis of aqueous solutions of ClO– and ClO–2 has been investigated using pulse and steady state methods. The absorption spectrum of ClO has been identified (λmax= 280 nm) and the complete reaction mechanism has been established in the case of ClO– and proposed in the case of ClO–2. The following rate constants have been evaluated (units of M–1 s–1): e–aq+ ClO–→ Cl–+ O–(5.3 ± 1.0)× 1010, e–aq+ ClO–2→ ClO–+ O–(4.5 ± 0.5)× 1010, OH + ClO–→ ClO + OH–(9.0 ± 0.5)× 109, OH + ClO–2→ ClO2+ OH–(6.3 ± 0.5)× 109, O–+ ClO–→ ClO + O2–(2.4 ± 0.1)× 108, O–+ ClO–2→ ClO2+ O2–(1.9 ± 0.1)× 108, 2ClO → Cl2O2 1.5 × 1010(2k) Values of the radical and molecular yields obtained for dilute alkaline solution are: G(e–aq)+G(H)= 2.92 ± 0.05, G(OH)= 2.41 ± 0.12, G(H2)= 0.42 ± 0.02 and G(H2O2)= 0.70 ± 0.01.Item Photochemistry and Radiation Chemistry of Anthraquinone-2-sodium-sulphonate in Aqueous Solution: Part 1.—Photochemical Kinetics in Aerobic Solution(Journal of the Chemical Society : Faraday Transaction - I. The Chemical Society, London. 1972, 68 (4), 1972) Clark, K. P.; Stonehill, H. I.When aqueous solutions of anthraquinone-2-sodium-sulphonate (D) are photolyzed the quinone becomes hydroxylated and (in the absence of oxygen) reduced. On the basis of the kinetics of the photohydroxylation in air or oxygen saturated solutions (pH 2–14), two alternative mechanisms are proposed, the 3D*/S (S = H2O or OH–) and the 3D*/D. In the former, D attacks S to produce an adduct DOH– which is converted by ground-state D to the radical DOH·. In the latter, 3D* attacks D to form a solvent caged radical pair {D·+ D·–}, the D·+ constituent then reacting with S to give OH· radicals which with D yield DOH·. This intermediate is converted by oxygen to hydroxy product. Neither continuous irradiation kinetics nor conventional µs flash photolysis permits discrimination between these schemes. The thermodynamic feasibility of OH· production by the 3D*/D reaction is demonstrated.Item Photochemistry of 1,3-Dichloro-tetrafluoroacetone: Part 3.—Quenching of the Excited States(Journal of the Chemical Society : Faraday Transaction - I. The Chemical Society, London. 1972, 68 (2), 1972) Hackett, Peter A.; Phillips, DavidThe quenching of the excited singlet and triplet states of 1,3-dichloro-tctrafluoroacctone by various molecules is reported. Correlation of results with decomposition data indicate that for 310 nm excitation, some 25-30 % of the decomposition products arise from the singlet state, the remainder from the triplet state. The various mechanisms by which the excited states are quenched by different molecules arc discussed, and rate-constant data compared with that for hcxafluoroacctoncItem Photochemistry of 1,3-DichIoro-tetrafluoroacetone: Part 2.—The Triplet State(Journal of the Chemical Society : Faraday Transaction - I. The Chemical Society, London. 1972, 68 (2), 1972) Hackett, Peter A.; Phillips, DavidQuantum yields of S1→ T1 intersystem crossing in 1,3-dichloro-tetrafluoroacetone have been measured using the technique of biacetyl sensitization. The vibrationally-relaxed singlet state of the molecule intersystem crosses to a dissociative triplet with quantum yield 0.92. Vibrationally-excited singlet-state molecules do not intersystem cross, but may dissociate in two ways.Item Photochemistry of 1,3-Dichloro-tetrafluoroacetone: Part 1.—The Singlet State(Journal of the Chemical Society : Faraday Transaction - I. The Chemical Society, London. 1972, 68 (2), 1972) Hackett, Peter A.; Phillips, DavidThe variation of the fluorescence quantum yield of 1,3-dichloro-tctrafluoroacetone with pressure of ketone and added gases is reported for several different exciting wavelengths. Fluorescence decay times were also measured. A mechanism is proposed to account for the results, and rate constants lor vibrational relaxation, fluorescence and non-radiativc decay processes tabulated. These are compared with similar results for other fluorinated ketones.Item Photochemistry of Aromatic Compounds: Part 5.—Measurement of Quantum Yields of Triplet State Formation by Flash Photolysis(Journal of the Chemical Society : Faraday Transaction - I. The Chemical Society, London. 1972, 68 (1), 1972) Donckt, E. Vander; Lietaer, D.The quantum yields of triplet-state formation of 1,2-benzanthracene, 1,2,5,6-dibenzanthracene, tetracene and 2-naphthylamine have been measured using the effect of organometallic compounds as dimethylmercury, tetramethyllead and tetramethyltin on fluorescence intensities and optical densities of triplet to triplet absorption. The quantum yields of triplet state formation of aromatic hydrocarbons can be obtained from the results of flash photolysis experiments only, although the method which involves relative fluorescence measurements is usually preferable especially for viscous solvents or relatively weak heavy atom quenchers.