Decay of Quasifree Electrons in Pulse-Irradiated Liquid Hydrocarbons

Abstract

The decay of the ion current in pulse‐irradiated hydrocarbons in a parallel‐plate ion chamber has been observed in the nsec‐μsec time range during which time the major contribution to the ion current is the quasifree, high mobility electron. At dose rates of 10¹⁵ eV cm⁻³/10⁻⁸ sec the electron current decay is exponential with a half‐life ranging from $\text{∼5\hspace{0.17em}}\mathrm{nsec}$ (cyclopentane) to $\text{>400\hspace{0.17em}}\mathrm{nsec}$ (n‐hexane). At higher dose rates, however, deviation from the exponential decay occurs and second‐order decay is approached at the highest doses/pulse ${\text{(6.5× 10}}^{16}\hspace{0.17em}{\mathrm{eV‐cm}}^{\text{−3}}{\text{/10}}^{\text{−7}}\hspace{0.17em}\sec )$ studied. This change from pseudo‐first‐order to second‐order kinetics is interpreted as a change in the electron decay from an attachment type process to electron‐ion recombination. Absolute rate constants for the electron reacting with several solutes in n‐hexane were also determined; these are $k_s{\mathrm{(e}}^{-}+{\mathrm{CCl}}_4{\mathrm{)\hspace{0.17em}=\hspace{0.17em}k}}_s{\mathrm{(e}}^{-}{\mathrm{+\phi }}_2{\text{)=1.0± 0.1× 10}}^{12}{\mathrm{,\hspace{0.17em}k}}_s{\mathrm{(e}}^{-}+{\mathrm{I}}_2{\text{)=2± 1× 10}}^{11}{\mathrm{,\hspace{0.17em}k}}_s{\mathrm{(e}}^{-}+{\mathrm{H}}_2\mathrm{O}{\mathrm{)\simeq \; k}}_s{\mathrm{(e}}^{-}+\mathrm{benzene}{\text{)\hspace{0.17em}≤ 1× 10}}^9,$ and $k_s{\mathrm{(e}}^{-}+{\mathrm{O}}_2\mathrm{,\hspace{0.17em}}{\mathrm{CO}}_2\mathrm{,\hspace{0.17em}}{\mathrm{N}}_2\mathrm{O}\mathrm{,\hspace{0.17em}}{\mathrm{SF}}_6{\text{) ≤ 2× 10}}^8{M}^{\text{−1}}·{\mathrm{sec.}}^{\text{−1}}$