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The photolysis of potassium cobaltioxalate in dilute acid solution Doering, Juergen Gerhard Walter

Abstract

A new sensitive spectrophotometric method for the direct determination of Co²⁺ ion in the presence of excess Co(III) was developed. Using this method the primary quantum yields for the photochemical decomposition of potassium cobaltioxalate were determined at pH 3 and 0°C over a wide range of wavelengths. The values for the various mercury lines were found to be: 280 mu, .369; 302 mu, .329; 313 mu, .362; 334 mu, .279; 365 mu, .244; 405 mu, .108; 435 mu, .067; 578 mu, ≤ .00033. The quantum yield for cobaltous ion formation is twice the primary quantum yield. No dependence of the quantum yield on the cobaltioxalate concentration was detected. The results are expected to be essentially the same in neutral solution because the instability constant of cobaltioxalate is extremely small. Correlation of the quantum yields with the absorption spectrum showed that photoactivity is considerable both for the electron transfer peak (in the U.V.) and the first d - d band (in the blue spectral region). Gaussian extrapolation of the absorption bands shows that a constant level of photoactivity cannot be directly assigned to each band. Further treatment of the data indicates that the quantum yields can be represented as two different functions of the logarithm of the light energy which however cannot be directly related to the two different types of transitions. The results are finally explained on the basis of internal conversion between the d - d and charge transfer bands.

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