Journal of Physical Chemistry A, Vol.117, No.11, 2287-2293, 2013
Spur Reactions Observed by Picosecond Pulse Radiolysis in Highly Concentrated Bromide Aqueous Solutions
The formation of the well-known product Br-3(-), observed in the steady-state radiolysis of highly concentrated Br- aqueous solutions, has now been directly observed at ultrashort times corresponding to the relaxation of the spur. The transient absorption induced by picosecond pulse radiolysis of 6 M Br- aqueous solution was probed simultaneously at 260 nm with the third harmonic laser wave and from 350 to 750 nm with a supercontinuum generated by the fundamental laser wave. This approach allows several transient radiolytic species to be followed in parallel, particularly the solvated electron, BrOH-center dot, Br-2(-center dot), and Br3-. The kinetics measured within 4 ns at 260 and 370 nm clearly exhibit that the decay of Br-2(center dot-) is correlated with the formation of Br-3(-). In highly concentrated Br- solutions, the OH center dot radical is fully replaced by Br-2(center dot-), and the spur kinetics of OH center dot radical in pure water is comparable with that of Br-2(-center dot). Model calculations indicate that the main OH center dot radical combination product H2O2 in pure water has formation kinetics similar to that of Br-3(-) in 6 M Br- solutions. Moreover, they point out that oxidation of Br- occurs within the electron pulse both by direct energy absorption and by scavenging of the water radical cation, H2O.