A TEMPERATURE-DEPENDENT KINETICS STUDY OF THE AQUEOUS PHASE REACTIONS OH+SCN--]SCNOH- AND SCN+SCN-REVERSIBLE-ARROW(SCN)2-

A laser flash photolysis-long-path absorption technique was employed to investigate the kinetics of the aqueous phase reactions [GRAPHICS] as a function of temperature in the range 277-321 K. On the basis of analyses of double-exponential (SCN)2- appearance temporal profiles, the following temperature-dependent rate coefficients were determined: In k1(T) = (29.614+/-0.636)-(1900+/-190)/T M-1 s-1, ln k3(T) = (23.459+/-1.259)-(271+/-374)/T M-1 s-1 and ln k-3(T) = (29.182+/-0.534)-(5580+/-160)/T s-1; the uncertainties in the above Arrhenius expressions are 1sigma and represent precision only. The enthalpy change associated with reaction (3) was evaluated on the basis of kinetic data and measurements of the equilibrium concentration of (SCN)2- as a function of [SCN-] and T; a value DELTAH = -8.8+/-2.8 kcal mol-1 was found to be consistent with all data.