ION RECOMBINATION RATES IN RARE-GAS CATION HALIDE ANION SYSTEMS .3. XEBR-ASTERISK AND XEI-ASTERISK

The techniques of electron pulse radiolysis and emission spectroscopy have been used to determine the ionic recombination rate constants, Xe 2+ + X- + Xe --> alpha XeX + 2Xe in the formation of the XeBr* and Xe I exciplexes. These values show the typical pressure dependence of an increase to a maximum value of a approximately 3 X 10(15) M-1 s-1 (al pha approximately 4 X 10(-6) cm3 s-1) before the onset of diffusion co ntrolled reaction. The comparison of the Xe2+/Br- data to the predicti ons of the Langevin-Harper diffusion controlled and Bates termolecular theories show that the experimental values are far larger and peak at much lower pressures than calculated, indicating that an additional m ode of recombination is occurring. This is attributed to the electrost atic tidal pathway, observed previously in Xe2+/Cl- and Kr2+/Cl-recomb ination. In contrast the Xe2+/I- measured peak is in excellent agreeme nt with the Bates prediction and at high pressures has rate constants even larger in magnitude than the Langevin-Harper diffusion controlled values. The application and extension of these theories to this syste m are discussed.