Positron Annihilation in Five- and Six-Carbon Liquid Hydrocarbons

Position annihilation rates have been measured for a series of five‐ and six‐carbon liquid hydrocarbons containing varying degrees of unsaturation. Values for ${\tau }_2$ , the long lifetime (in nanoseconds), and its intensity, $I_2$ (listed in parentheses), were determined for the following compounds: trans‐3‐hexene, 3.35 ± 0.11(39.0 ± 4.0%); 1‐hexyne, 3.42 ± 0.04(31.1 ± 2.9%); 3‐hexyne, 3.13 ± 0.05(25.2 ± 2.5%); 1,3‐hexadiene, 3.54 ± 0.07(30.5 ± 2.0%), trans‐1,4‐hexadiene, 3.29 ± 0.16(27.1 ± 3.5%); 1,5‐hexadiene, 3.50 ± 0.06(30.3 ± 2.0%); 1,3‐pentadiene, 3.5 ± 0.2(30.0 ± 4.5%); 1,4‐pentadiene, 3.4 ± 0.2(29.6 ± 4.5%). Reduced annihilation rates, ${\mathrm{(\sigma \upsilon )}}_{\mathrm{obs}}$ , were computed and compared with values predicted from index of refraction data using the methods of Gray et al. The data do not support the proposition that positron annihilation rates bear a strong fundamental relationship to indices of refraction. Partial annihilation rates for a number of functional groups and various bonds were also computed and are discussed.