Positron annihilation and electron densities in organic liquids

Abstract

The effective electron density for positron annihilation in substituted aliphatic and aromatic liquid compounds has been determined. For the aliphatic hydrocarbons the molecular electron density N_e increases linearly with an increase in chain length and is equal to the sum of the partial electron densities of the substituent methyl (N_e(CH₃) = 1.18) and methylene (N_e(CH₂) = 1.28) groups.The values are approximately 10% lower for aromatic systems. The partial electron densities of substituted halogen atoms increase with atomic number and are: fluorine (9.3), chlorine (10.0), bromine (14.4) and iodine (23.0). For the aliphatic alcohols the partial N_e(OH) value decreases from 1.35 in methanol to 0.86 in octanol.