PIVALIC ACID AS COMBINED BUFFER AND SCAVENGER FOR STUDIES OF CLOUD-WATER CHEMISTRY WITH PULSE-RADIOLYSIS

The reactions of cloud water with transition-metal ions may be studied using pivalic acid as buffer and .OH scavenger. Commonly used phosphate buffers form strong complexes that may have an important effect on reaction kinetics. Low solubility products limit transition-metal ion concentrations to very tow levels (micromolar). With pivalic acid as buffer, we can increase the Cu-II concentration typically by a factor of 340. At the same time better buffer characteristics and less complex formation is achieved. The scavenger efficiency equals that of tert-butyl alcohol. The rate data and the spectra of pivalic acid radicals have been measured in N2O-saturated solutions of pivalic acid. The acid constant was found to be 4.9 +/- 0.1. The rate constants for the reaction of .OH with pivalic acid have been re-evaluated: k[(CH3)(3)CCO2- + .OH] = (7 +/- 2) x 10(8) dm(3) mol(-1) s(-1) and k[(CH3)(3)CCO2H + .OH] = 6.5 x 10(8) dm(3) mol(-1) s(-1). The importance of including reactions like H. + .CH2(CH3)(2)CCO2H in the reaction model is shown. The rate constants for the recombination of pivalic acid radicals are: k[2.CH2(CH3)(2)CCO2H] = (7 +/- 1) x 10(8) dm(3) mol(-1) s(-1), k[.CH2(CH3)(2)CCO2H + .CH2(CH3)(2)CCO2-] = (7 +/- 3)x 10(8) dm(3) mol(-1) s(-1) and k[2.CH2(CH3)(2)CCO2-] = (3.7 +/- 0.4) x 10(8) dm(3) mol(-1) s(-1).