The concentration-modulation approach to the study of absorption spectra of atoms and molecules developed with mode-locked dye lasers is extended in this paper to continuous-wave lasers. A 'gain' theory is developed for use with C.W. lasers and a comparison is made between the 'gain' measurements of our C.W. experiments and those of earlier studies using pulsed lasers. The experimental agreement between the measured C.W. 'gain' and the pulsed 'gain', after correcting for differences between the experimental arrangements employed, provides strong support for the 'gain' theory developed here. It is clearly seen that by means of this theory and the derived equations it will be possible to evaluate species concentrations where the state lifetimes are known, or the lifetimes where the concentrations are known. These studies provide a firm foundation for expansion of the applicability of this highly sensitive absorption technique for kinetic and spectroscopic investigation of chemical systems.

M N DO calculations of the most favoured conformations of antitumour 3-(hydroxymethyl) -3-methyl-1 -(4-X-pheny1)triazenes (2) indicate N-CH,OH bond lengths of over 1.49 A (lengthened by electronwithdrawing groups), correlated with high lability under physiological conditions (t,lz under 1 s ) .Hydrolysis rates of 20 (X = NO,) in methanol/acetonitrile containing water were determined using high performance liquid chromatography (HPLC) and extrapolated to give a tl/, of 4 3 s at 100% water.Modelling of decomposition pathways of 2d (X = CH,) using M N D O predicts that concerted loss of formaldehyde is not favoured. Loss of [H2COH]+ from nitrogen protonated 2d is also a high energy process, but loss of formaldehyde from deprotonated 2d seems feasible under basic conditions. Under acidic conditions the energetically preferred process is loss of water from protonated 2d to give an iminium ion, even though the required initial 0-protonation is disfavoured over protonation on nitrogen.Paper 2/06822B

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Among the rare earths, Cerium (Ce) and several of its compounds find a wide range of industrial applications. Cerium is also that most abundant of the rareearth elements, being found in several minerals (e.g. monazite) in high proportions. It is generally extracted from fractions obtained in the processing of these minerals. Potassium stearate has been used as one of the extracting agents for Ce (IV). In this study, the feasibility of extractingcerium both as Ce (IV) and Ce (In), by precipitation with sodium and potassium salts for stearic, lauric, palmitic, capric, oleic acids; mixture of these acids and saponified coconut oil was investigated. The main objtive was to study the extractibility of Ce (III) and Ce in coconut oil saponified by sodium hydroxide (NaOH); because both coconut oil and sodium hydroxide are available in Sri Lanka, and the method if successful could be economically used on a large scale. The extractibilities of Ce (111) and Ce (IV) ions were determined on a quantitative basis, by their conversion into acylates in each of the above systems over a range of pH values. The results showed that (a) the extent of extraction of Ce (III) and Ce (IV) are reasonably high in the saponified coconut oil, (b) Ce (IV) is best extracted with sodium salts and Ce (111) with potassium salts at a pHvaluearound 5, (c) more than 65 % of Ce (111) can be extracted by sodium salts in the pH range of 3.5-6.8 under carefully controlled conditions. Therefore coconut oil saponified by sodium hydroxide can be considered as a promising extracting medium for Ce (IV) ions especially, while the oil saponified by hydroxides of both sodium and potassium is promising for the extraction of Ce (111) ions.

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