| Abstract
| - The temperature dependence of the absorption spectrum of the formation and decay of (SCN)2•-, a well-characterized dimer anion, was investigated at temperatures from 25 to 400 °C. The absorption peak wasfound to shift to longer wavelength with temperature (red shift), from 470 nm at 25 °C to 510 nm at 400 °C.The equilibrium constants K1 and K2 for the reactions SCNOH•- ⇄ SCN• + OH- and SCN• + SCN- ⇄(SCN)2•-, respectively, were found to decrease with temperature. Due to the considerable decrease of K2with temperature, a rise in temperature shifts the reaction in favor of SCN•, so the observed yield of (SCN)2•-at high temperatures is strongly dependent on the SCN- concentration. As the SCN• concentration could beas high as or even higher than the (SCN)2•- concentration at high temperatures, a pseudo-first-order decay ofSCN• has to be taken into consideration to account for the overall decay of (SCN)2•-. Using the kineticparameters obtained in this work and available in the literature, the decay profiles of (SCN)2•- can be wellreproduced for any temperature and KSCN concentration considered. A combination of the simulation andthe experimental results reveals a decrease of εmax of (SCN)2•- with temperature; the degree is ∼30% for arise from 25 to 400 °C.
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