Precise Measurements of W, the Mean Energy Required for Ion-Pair Formation in Gases I. Alkanes

Abstract

Ionization currents were measured for the complete stopping of ⁶³Ni beta rays in N₂ and in alkane isomers at temperatures 25–200°C and pressures between 400 and 2700 torr. The mean energy expended per ion pair formed, $W$ (beta), was determined from the ratio of ion current in nitrogen to that in the sample at equal electron densities. No dependency of $W$ upon temperature or pressure was observed within the experimental precision of ± 0.1%. Using $\mathrm{W\; (}{\mathrm{N}}_2\text{)\hspace{0.17em}=\hspace{0.17em}34.6}$ eV/ion pair for reference, relative values of $W$ in electron volts/ion pair were found to be 26.94 for methane, 24.18 for ethane, 23.69 for propane, 23.19 for n‐butane, 22.82 for n‐pentane, 22.62 for n‐hexane, 22.47 for n‐heptane, 23.52 for 2‐methylpropane, 23.07 for 2‐methylbutane, 23.42 for 2,2‐dimethylpropane, 22.80 for 2‐methylpentane, 22.81 for 3‐methylpentane, 22.81 for 2,3‐dimethylbutane, and 22.88 for 2,2‐dimethylbutane.