Geminate Charge Recombination in Liquid Alkane with Concentrated CCl4: Effects of CCl4 Radical Anion and Narrowing of Initial Distribution of Cl-

Dynamics of radical cations and electrons in an admixture of a linear saturated hydrocarbon (n-dodecane) and halocarbon (carbon tetrachloride, CCl4) were investigated by picosecond electron beam pulse radiolysis. The decay of thermalized electrons (e(th)(-)) observed in infrared transient photoabsorption were simply accelerated by the addition of CCl4, giving a high rate constant of 2.3 x 10(11) mol(-1) dm(3) s(-1). The decrease of the initial yield of e(th)(-) was quantified by C-37 (50 mmol), which is linked to the reaction of epithermal electrons (e(-)) with CCl4. In contrast, the n-dodecane radical cation (RH2 center dot+) monitored in the near-infrared indicated a convex-type dependence of the decay rate on CCl4 concentration, although the initial yield of RH2 center dot+ remained almost constant up to a much higher CCl4 concentration. The decay of RH2 center dot+ was analyzed by Monte Carlo simulations of geminate ion recombination with e(th)(-), chlorine anion (Cl-) formed via dissociative electron attachment, and CCl4 radical anion. The results showed a good agreement with the experiments by considering two assumptions: (1) CCl4 radical anion formed via e(th)(-) attachment and (2) narrowing of the initial distribution of Cl-. The decrease in the initial yield of RH2 center dot+ at high CCl4 concentration was well explained by immediate decomposition of CCl4 center dot+ to CCl3+ and hole transfer from CCl4 center dot+ to adjacent RH2 without diffusive motion of the reactants. Time-dependent density functional theory supported the spectroscopic assignment of intermediate species in the n-dodecane/CCl4 system. The present results would be of help in understanding the electron capture reaction in multicomponent systems such as a chemically amplified resist in lithography.