Browsing by Author "Kemp, Terence J."

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Absorption spectrum, lifetime and photoreactivity towards alcohols of the excited state of the aqueous uranyl ion (UO 2+2)
(Journal of the Chemical Society : Faraday Transaction - I. The Chemical Society, London. 1974, 70 (1-6), 1974) Hill, Richard J.; Kemp, Terence J.; Allen, David M.; Cox, Alan
Microsecond flash photolysis of solutions of uranyl salts in water, H3PO4, H2SO4 and other media yields an intense, but short lived transient absorption spectrum in the region of 570 nm which exhibits vibronic structure with an average band separation of 580 cm–1. The decay of the transient in water was determined by laser flash photolysis to be first order with k1= 8.02 × 105 s–1, but with a considerable isotope effect (k1(D2O)= 4.20 × 105 s–1). k1 accords with the lifetime of the luminescence of aqueous UO2+2 ion determined by single photon counting (k1= 3.85 × 105 s–1). Both the 570 nm absorption and the emission (as determined by both single photon counting and conventional fluorimetry) are quenched on addition of various alcohols, the Stern–Volmer quenching constants closely correlating with the absolute quenching constants for the transient determined by laser flash photolysis. Large isotope effects were found for quenching by deuterated methanol, isopropanol and cyclohexanol both of the transient absorption and the emission. We conclude that the same electronic state of UO2+2 is responsible for (i) emission to the ground state, (ii) the absorption at 570 nm to a higher excited state and (iii) the photo-oxidation of aliphatic alcohols, principally by a process of abstraction of an H atom bonded to carbon from a —CH2OH or [double bond, length as m-dash]CHOH group.
Electron Spin Resonance Detection of Radical Intermediates During Photo-oxidation by Metal Ions in Solution
(Journal of the Chemical Society : Faraday Transaction - I. The Chemical Society, London. 1974, 70 (1-6), 1974) Greatorex, David; Hill, Richard J.; Kemp, Terence J.; Stone, Thomas J.
Irradiation of fluid solutions of ceric and uranyl ions in various organic media in the temperature range 140–290 K gives rise in many cases to well-resolved e.s.r. spectra of solvent-derived radicals, enabling characterisation of the photolytic process. Whilst UO2+2 photo-oxidises predominantly, but not exclusively, by means of abstracting a hydrogen atom from carbon adjacent to an activating site such as —OH or —CO2H, Ce(IV) attacks by a process of C—C fission; for example RCO2H yields R˙ and R′CH2OH yields, not R′ĊHOH as is customarily found at 77 K, but R′˙.
Inorganic photophysics in solution. Part 1.—Temperature activation of decay processes in the luminescence of tris(2,2′-bipyridine)ruthenium(II) and tris(1,10-phenanthroline)ruthenium(II) ions
(Journal of the Chemical Society : Faraday Transaction - I. The Chemical Society, London. 1978, 74 (05), 1978) Allsopp, Stephen R.; Cox, Alan; Kemp, Terence J.; Reed, W. John
The luminescence lifetimes of [Ru(bipy)3]2+ and [Ru(phen)3]2+ have been determined in a variety of media, over as wide a temperature range as feasible in each case (with a lower limit of 77 K). These results, together with a reinterpreting of certain others in the literature, indicate that the deactivation of the luminescent state of both complexes proceeds through two energy-controlled pathways. For [Ru(bipy)3]2+ one of these is characterised by a relatively large activation energy (≈ 48 kJ mol– 1) which dominates at T[gt-or-equal] 270 K, whilst the other route, which dominates at T < 130 K has an activation energy ≈ 2 kJ mol– 1 in fluid media, but only 0.64 kJ mol– 1 in a polymer film. In 9 mol dm– 3 LiCl + water (H2O and D2O) media, the low-energy term is 1.77 kJ mol– 1 above the glass transition region, but 0.65 kJ mol– 1 below Tg, indicating the importance of solvation forces. An exactly analogous pattern of results is shown by [Ru(phen)3]2+. A simple energy-level model is proposed which covers the luminescence behaviour from cryogenic to ambient temperatures.