Positive Ion Scavenging in the Radiolysis of Liquid Chloroform

Abstract

The effects of the positive ion scavengers NH3 and n-C4H9OH, on the organic product yields in the radiolysis of liquid CHCl3 at 25°C were investigated. As the solute concentrations increase, the values for G(CH2Cl2), G(C2HCl5), and G(C2Cl6) increase, G(sym-C2H2Cl4) and G(C2Cl4) remain unchanged, and G(CCl4) decreases. These results are consistent with a free radical mechanism for all the radiolysis products except CCl4. The decrease in G(CCl4) indicates that CCl4 is formed by a secondary positive ion reaction. The concentration dependence of this decrease can be described by the expression G(CCl4)O−G(CCl4)S=G(CCl4)O((α[S])1/2/{1+(α[S])1/2}), where G(CCl4)O is the 100-eV yield in the absence of a scavenger, and α is an empirical parameter proportional to the reactivity of the solutes, and [S] is the concentration of the scavenger in moles per liter. Values of α were determined for each solute and compared to published values determined in cyclohexane. In chloroform, values for α were 4–19 times larger than in cyclohexane suggesting that the solutes are more efficient in the alkyl halide than in the hydrocarbon. One mechanism accounting for this efficiency increase is the formation of anions by the free electrons in the alkyl halide. This anion formation increases the average lifetimes of the ions in the alkyl halide and hence the efficiencies of the scavengers. The increase in the 100-eV yields of three of the products formed by the free radical mechanism indicates that the presence of a cation scavenger increases the radical yields. Thus, some of the charge neutralizations in pure CHCl3 do not produce radicals. This observation is in accord with the existence of the collisionally stabilized CHCl3− anion in the irradiated solutions. It is suggested that this anion may be an intermediate in the formation of CCl4.