Optical study of electrons and positive ions in pulse-irradiated liquid 3-methyloctane at low temperatures

Abstract

The spectrum of pulse-irradiated liquid 3-methyloctane at 127 K has maxima around 625 and 2100 nm. The latter is well-known as being due to the solvated electron (es−). The former is attributed to a positive ion because it is eliminated by the addition of triethylamine, but remains in solutions of electron scavengers, and is very similar to bands observed earlier by Louwrier and Hamill in glassy solutions at 77 K of higher hydrocarbons in CCl4 or CO2-bubbled 3-methylpentane. At temperatures of 127 K and less the initial decay rate of es− is greatly decreased by the addition of ∼6mol% triethylamine. The result is interpreted as indicating that at low temperatures the mobility of the initial hydrocarbon positive ion is much greater than that of either es− or the positive ion in triethylamine solutions, and therefore the initial hydrocarbon positive ion must be the parent radical cation which moves by resonance charge transfer. As the temperature of pure 3-methyloctane is raised from 103 to 153 K, the initial Gε650 decreases by about 30% while initial Gε2100 almost doubles; because of these and other observations it is tentatively suggested that a second solvated electron is also produced.