EFFECT OF ION-PAIRING ON ELECTRON SCAVENGING AND SOLVATED ELECTRON YIELD ENHANCEMENT IN METHANOL - A COMPARISON BETWEEN PULSE-RADIOLYSIS AND POSITRON LIFETIME SPECTROSCOPIC DATA

The influence of ion pairing on electron scavenging in nitrate solutions and the effect of amines on the enhancement of the electron yield, two particular processes previously observed in positron annihilation (PA) studies on positronium (Ps) formation in methanol, are examined by using picosecond pulse radiolysis (PR). These studies show that the scavenging of the precursors of the solvated electron (e(sol)- does not depend on ion pairing while confirming previous results that ion pairing strongly affects the reaction of e(sol)- with LiNO3 and NH4NO3. The results from positronium annihilation studies agree with the precursor scavenging results for NO3- and NH4NO3; however, LiNO3 is a weaker electron scavenger. No increase in the initial e(sol)- yield is detected in PR in the presence of amines, whereas the Ps yield is significantly increased. These apparent differences can be explained if one considers the importance of the trap depth for the electron, whether it has been captured by a solute (LiNO3) or it has recombined with the positive ion (amines). In either case, in PR, the electron is lost for the free e(sol)- yield. In PA on the contrary, if both types of traps are shallow enough, the electron can still be picked off by the positron to form Ps.