Kinetic studies on the deamination of [Co(en)3](NCS)3

The loss of ethylenediamine from [Co(en)₃](NCS)₃ has been studied using isothermal weight loss methods. The reaction has been found to be catalyzed by NH₄SCN and piperidine hydrothiocyanate, and the reaction appears first order in catalyst. However, the reaction proceeds so slowly without a catalyst present that a reliable activation energy could not be obtained. For the catalyzed process, the activation energy appears to decrease slightly as the amount of catalyst used is increased, although the results are inconclusive when NH₄SCN is the catalyst. When piperidine hydrothiocyanate is the catalyst, the activation energy appears to decrease from 37.7 kcal mole^?1 to 29.4 kcal mole^?1 as the amount of catalyst increases from 0.5 to 8.0 mole percent. In all cases, the product turned dark after a few hours indicating some reduction as a complicating feature.     

Photoredox behaviour of trans and cis Co (III)-diisothiocyanatotetram(m)ine complexes

The trans and cis isomers of Co(NCS)₂(NH₃)₄⁺ and Co(NCS)₂(en)₂⁺ were prepared and characterized. Single-crystal X-ray diffraction showed that the first named was the trans isomer and established that the thiocyanates are N bonded. Photoredox quantum yields of the Co²⁺ ion on room temperature irradiation at 360 nm were found to be 0.065±0.001, 0.0082±0.001, 0.0088±0.0007 and 0.0040±0.0010 respectively. Other products measured were the thiocyanate ion and ammonia, but the relationships of these yields to Co²⁺ were not as expected for simple oxidation of thiocyanate and reduction of Co(III). On irradation in the presence of thiocyanate, a significant increase in yields occurs and this can be modelled in terms of scavenging of the thiocyanate radical from an initial caged radical pair giving picosecond estimates for the lifetime of this species of the order of tens of picoseconds, or in terms of photolysis of a thiocyanate/complex ion pair giving formation constant of 0.25±0.17, 0.12±0.04, 0.11±0.06 and 0.06±0.04 for the complexes in the sequence above. In all but the last instance these are in excellent agreement with the values estimated by fitting the thiocynate induced changes in the UV-visible spectra of the complexes, 0.34±0.25, 0.14±0.07, 0.09±0.07 and 0.60±0.07 respectively. Laser flash photolysis studies on the nanosecond and picosecond time-scale failed to reveal any direct spectroscopic evidence for a radical pair species, but the absorbance of (NCS)₂^-√ was seen in all four systems. The effects of added electrolytes and of viscosity on the formation and decay of this intermediate were investigated and are reported in detail.     

Spin-polarized low-energy positron beams and their applications

The production and use of low-energy (100 eV to 5 keV) high-intensity, spin-polarized positron beams is reviewed. Methods for obtaining beams with high polarization are discussed. Applications include studies of the moderation process, surface and bulk magnetism, optically active molecules, and the production of polarized anti-protons.This paper is based upon an invited talk given by A.R. at the International Symposium Production of Low-Energy Positrons with Accelerators and Applications (Justus-Liebig-Universität Giessen, FRG, 25–27 September 1986)     

SERRS and visible extinction spectroscopy of copper chlorophyllin on silver colloids as a function of pH

A study of sodium copper chlorophyllin adsorbed on silver colloids (CuChl/Ag) is conducted using surface-enhanced resonance Raman scattering (SERRS) and visible extinction spectroscopy to examine how the system changes as a function of pH. Initially at basic pH, SERRS signal is not detected even though CuChl is adsorbed onto the silver surface and deprotonated. Upon decreasing the solution pH slightly, colloidal aggregation is induced, evidenced by the broadening of the visible extinction spectra. The larger aggregates possess a surface plasmon that is in resonance with the laser excitation frequency (633-nm) and SERRS signal is detected. As the acid protonates CuChl, the overall negatively-charged surface approaches neutrality which induces more aggregation. Complete protonation of CuChl by pH 4.6 results in colloidal precipitation. However, when aggregation is halted about pH 5, adding NaOH(aq) to the system maintains the extent of aggregation and an intense SERRS signal is detected at basic pH.     

The measurement of electrohydro-dynamic motion with an optical probe

An experimental comparison of a Doppler anemometer with a fringe anemometer has been made under conditions where the number of scattering particles is small. The Doppler system was found to be more suitable for use in purified liquids and was subsequently employed to monitor electrically-induced liquid motion during charge-mobility measurements. A simple technique is described which enables some forms of transient liquid motion to be measured with a spectrum analyser.