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Resonance Raman and electronic absorption studies of iron protoporphyrin IX chloride (hemin) in non-ionic Triton X-100 micelle in the absence and presence of hindered imidazole (2-methylimidazole and 1,2-dimethylimidazole) and unhindered imidazole under various experimental conditions are reported. Hemin undergoes photoreduction at the metal center, both in the absence and presence of hindered imidazole, in anaerobic, alkaline and neutral pH conditions on photoexcitation by laser radiation at 441.6 and 457.9 nm. It is inferred from this study that only the monomer hemin encapsulated within the micelle under the alkaline pH conditions is photoreducible. The photoreduction of hemin in this micelle occurs from an electron transfer as a result of dissociation of coordinated hydroxyl ion to the iron atom in the photoexcited state, which may also involve the OH ! Fe charge transfer transition around 360 nm.

We report a resonance Raman study on free-base tetraphenylporphine (H 2 TPP) and its chemically prepared diacid dispersed in polymethylcyanoacrylate (PMCA). Photoexcitation of the neutral porphine by laser light leads irreversibly to the formation of the diacid, with the p-cation radical as intermediate species.Resonance Raman (RR) spectra of the diacid dispersed in the polymer obtained with 441.6 nm in the wavenumber region of 100-1650 cm −1 are recorded. Wavenumbers with other excitation lines are also reported for the diacid species. Some bands assigned to out-of-plane vibrational modes and forbidden under ideal D 2h symmetry are also observed in the resonance Raman spectra of the diacid. These bands arise from the out-of-plane distortions, which reduce the symmetry of the molecule. These findings are supported by the electronic absorption studies of the diacid in the polymer.

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Photoinduced electron transfer from axially coordinated electron donor to hemin in aqueous cetyltrimethylammonium bromide and sodium dodecyl sulfate micelles under various pH conditions with and without hindered/unhindered imidazoles was investigated. Photoreduction of hemin in the former micelles under anaerobic conditions in alkaline and neutral aqueous medium takes place by electron transfer from axially coordinated hydroxyl ion to an FeIII atom in the photoexcited state. In sodium dodecyl sulfate micelles, hemin is photoreducible only at alkaline pH and under anaerobic conditions in the presence of alcohol and imidazoles. Photoreduction appears to depend on the immediate local environment of hemin in the micelles. Copyright © 2003 John Wiley & Sons, Ltd.

Self-excited push-pull vacuum tube oscillator is one of the most commonly used oscillators in radio frequency (RF)-ion plasma sources for generation of ions using radio frequency. However, in spite of its fundamental role in the process of plasma formation, the working and operational characteristics are the most frequently skip part in the descriptions of RF ion sources in literatures. A more detailed treatment is given in the present work on the RF oscillator alone using twin beam power tetrodes 829B and GI30. The circuit operates at 102 MHz, and the oscillation conditions, stability in frequency, and RF output power are studied and analyzed. A modified form of photometric method and RF peak voltage detection method are employed to study the variation of the oscillator output power with plate voltage. The power curves obtained from these measurements are quadratic in nature and increase with increase in plate voltage. However, the RF output power as measured by photometric methods is always less than the value calculated from peak voltage measurements. This difference is due to the fact that the filament coil of the ordinary light bulb used as load/detector in photometric method is not a perfect inductor. The effect of inductive reactance on power transfer to load was further investigated and a technique is developed to estimate the amount of power correction needed in the photometric measurement result.

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