Mary A. Jamieson

Photochemical degradation of chlorinated dioxins, biphenyls phenols and benzene on semiconductor dispersion

Abstract The degradation of various aromatic pollutants present in aqueous media was performed using suspensions of semiconductor particles under illumination. The efficiency of the process has been shown to be dependent on the nature of the catalyst. The complete mineralization of halophenols has been observed after long term experiments.

Photophysical and photochemical primary events in semiconductor particulate systems. Colloidal CdS with methylviologen

Abstract The photogenerated electron/hole pairs in excited CdS, produced by irradiation (355 nm) from a Nd:YAG mode-locked laser, yield a luminescence which decays in ≤ 30 ps. Time-resolved change-in-absorbance spectra of CdS in the presence of methylviologen MV 2+ (degassed) show formation of MV + and its dimer (MV + ) 2 (λ max ∼ 530 nm) in ∼ 1 ns.

Picosecond spectroscopy of transition metal complexes

Spectrometrie des metaux carbonyle, des complexes metalliques avec des coordinats mono- et bidentes, des complexes metalliques dinucleiaires et des porphyrines metalliques

Interligand pockets in polypyridyl complexes. The crystal and molecular structure of the Cr(2,2′,2″-terpyridine)23+ ion

A single crystal X-ray study reveals that the title compound possesses a distorted meridional configuration; the interligand pockets are such that, in aqueous solutions, the CrIII core may be considered solvated by water molecules.

Picosecond laser spectroscopy of chromium(III) complexes. Probing the photophysics of 4T2 excited states of Cr(bpy)33+ and Cr(4,7-Me2phen)33+ ions in aqueous solution

Abstract Picosecond laser techniques have been used to probe the photophysics of the short-lived 4 T 2 excited states of Cr(bpy) 3 3+ and Cr(4,7-Me 2 phen) 3 3+ complexes (bpy is 2,2′-bipyridine and 4,7-Me 2 phen is 4,7- dimethylphenanthroline). Contrary to the previously reported value of the lifetime of ( 4 T 2 )Cr(bpy) 3 3+ (≈10 ps) obtained from resonance Ramans studies(3.2 ns laser pulse), luminescence and time-resolved absorption spectroscopy using mode-locked Nd : YAG laser pulses of 30 ps (fwhm) indicate that the lifetime of these quartet states is ≈10–20 ns.

Oxidative substitution reaction of the osmochrome Os(OEP)[P(OMe)3]2 in chlorinated solvents

Abstract Steady state photolysis of Os(OEP)[P(OMe)3]2, where OEP is octaethylporphine, in the chlorinated solvents CH2Cl2, CHCl3 and CCl4 at 365 and 405 nm and at 22 °C results in the formation of an osmium(IV) porphyrin identified as Os(OEP)Cl2. The reaction is described as an oxidative substitution reaction. The rate of formation of the photolysis product increases as the solvent varies in the order CH2Cl2

Ground-state quenching of (2T1/2E)Cr(NN))3+3. Anion and temperature dependence

Abstract The emission lifetimes of (2T 1 / 2 E)Cr(NN) 3+ 3 , where NN is bpy (2,2′-bipyridine) and phen (1,10-phenanthroline), in aqueous solutions in the presence 1.0 M HClO 4 , KNO 3 , NaBr, NaBrO 3 , HCl, Na 2 SO 4 , H 2 SO 4 and neat water media have been determined as a function of the concentration of ground state Cr(NN) 3+ 3 in order to quantify the ground-state quenching phenomenon. This process is described by 2 k obs = 2 k o + 2 K g [Cr(NN) 3+ 3 ], where 2 k o (= 1/ 2 τ o ) is the first-order rate constant for decay of 2 T 1 / 2 E and 2 K g is the second order rate constant for ground-state quenching. In neat water, 2 τ is invariant, 0.25 ± 0.03 ms for Cr(phen) 3+ 3 , but in the presence of anions 2 τ decreases with increase in [Cr(phen) 3+ 3 ]; 2 k g values decrease as the anion varies ClO − 4 > NO − 3 > Br − > BrO − 3 ∼ SO 2− 4 > Cl 2− > HSO − 4 . For Cr(bpy) 3+ 3 , 2 τ is 0.068 ± 0.008 ms in neat water, and the presence of anions have no effect in 1.0 M media at 22 °C. Anion mediation of ground-state quenching is proposed as arising from encounters of excited-state and ground-state ion pairs to form the ‘ion-bridged excimer’ *{Cr(NN) 3+ 3 ⋯X − ⋯Cr(NN) 3+ 3 }. Temperature dependence studies of these encounters give ΔH # g = 4.2 kcal/mol and ΔS # g = −9 eu Cr(phen) 3+ 3 in the temperature range 13–42°C. At ∼15 °C, ground-state quenching is observed for Cr(bpy) 3+ 3 in 1.0 M NaCl medium as a result of lowering 2 K o .

Kinetic studies of the oxidative photosubstitution reaction in the charge transfer photochemistry of Os(OEP)[P(OMe)3]2 (OEP≡octaethylporphine) in hexane-halocarbon mixtures

Abstract The osmochrome Os II (OEP)[P(OMe) 3 ] 2 , where OEP is octaethylporphine, undergoes an oxidative photosubstitution reaction in hexane in the presence of chlorinated hydrocarbons (CH 2 Cl 2 , CHCl 3 , CCl 4 , CHCl 2 CH 3 and CH 2 ClCH 2 Cl) under steady state photolysis. The product has been identified as Os IV (OEP)Cl 2 . Both initial rates of reaction and quantum yields are, within experimental error, independent of whether the hexane-chlorinated hydrocarbon solutions are argon purged, air equilibrated, N 2 O purged or oxygen purged. The quantum yields increase with increase in CR 2 Cl 2 (R  H or Cl) concentration; limiting quantum yields are 0.0017 ± 0.0001 (CH 2 Cl 2 ), 0.25 ± 0.08 (CHCl 3 ) and 0.93 ± 0.10 (CCl 4 ). The reactivity of the chlorinated reactants is CCl 4 (280) > CHCl 3 (35) & >; CH 2 ClCH 2 Cl (1.4) ≈ CHCl 2 CH 3 (1.1) ≈ CH 2 Cl 2 (1.0) under the experimental conditions used; this order accords with expectations based on the CCl bond strengths. A mechanism is postulated in which the three essential steps are (L  P(OMe) 3 ) (i) Os(OEP)LL ⇌ Os(OEP)L + L (ii) Os(OEP)L + CR 2 Cl 2 → products and (iii) Os(OEP)LL + CR 2 Cl 2 → products The data are treated using both the conventional kinetic theory and the model of Noyes for the scavenging of photoproduced radical pairs in solution.

4 T 2 →2E Intersystem-crossing efficiency in the Cr(bpy)33+ and Cr(phen)33+ ions in aqueous media

Comparison of the photoaquation quantum yields of Cr(bpy)33+ and Cr(phen)33+ complexes in alkaline aqueous media, from direct irradiation into the spinallowed 4T2 manifold and into the spin-forbidden 2T1/2E states, indicates that the 4T2→2E intersystem-crossing (isc) yields are identical for the two complexes (ηiscca. 1).